JP4833671B2 - Semiconductor laser device, semiconductor laser device manufacturing method, and spatial light transmission system - Google Patents

Description

The present invention relates to a semiconductor laser device, a semiconductor laser device manufacturing method, and a spatial light transmission system.

  Spatial light transmission using infrared rays, represented by the IrDA (Infrared Data Association), is now widely used. Address books, schedules, and photographic data between portable terminals and personal computers. From the convenience that data such as can be easily transmitted without connecting electrical wiring, it is expected to become more widespread in the future.

  In recent years, with an increase in data capacity, the transmission rate has been increasing from 1 Mbps to 4 Mbps and 16 Mbps. In the future, transmission data will become high-quality photographic data and moving image data, and it is considered that the data capacity will further increase. Therefore, there is an increasing demand for further increasing the transmission speed.

  In general, when the transmission speed is increased, the transmission distance is shortened. However, there is an increasing demand for transmitting a long transmission distance at a higher transmission speed.

  Currently, in a spatial light transmission system such as IrDA, it is necessary to increase the light output of a light source to be used as the transmission speed increases and the transmission distance increases.

  Recently, an attempt to use an LD (laser diode) as a light source of a spatial light transmission system has begun. In order to increase the transmission speed and increase the transmission distance in the spatial light transmission system, it is essential to increase the output of the LD.

  However, when LD light is directly emitted into space, the LD light is highly coherent in spatial characteristics. Therefore, when the LD light enters the eye, it is collected on the retina and the light density on the retina is very high. There is a risk of enlargement and eye damage. For this reason, when emitting LD light to space, measures such as installing a diffusion plate at the location where LD light is emitted or molding the LD with a resin mixed with a diffusing agent are taken. Therefore, it is necessary to reduce the spatial density of light on the retina by reducing the spatial coherency of the image and increasing the imaging of light on the human retina. The above measure is referred to as “eye-safe” in the sense of “safe for eyes”.

  Further, when the mold diameter of the LD is increased, the eye-safe property is maintained even for light of higher output LD.

  For example, an LD module for a server needs to perform spatial light transmission over a longer distance and at a higher speed than a small LD module for a portable terminal. Therefore, a large-diameter LD module is used to increase the output of the LD. There is a need.

  An LD having an oscillation wavelength of 850 nm to 900 nm is used for the spatial light transmission system. This LD can be manufactured by using GaAs as a substrate and using GaAs, AlGaAs, GaInAs or the like as an active layer.

  In the semiconductor material constituting the LD, the following conditions (1) to (3) are basically required.

  (1) The carrier can be confined in terms of energy. That is, Eg (band gap energy) can be freely controlled, and in the case of the quantum well active layer, there is a sufficiently large ΔEg (difference in band gap energy) between the well layer and the barrier layer.

  (2) Light can be optically confined. That is, the refractive index can be freely controlled.

  (3) The lattice constant is not significantly different from that of the substrate.

  When an LD having an oscillation wavelength band of 850 to 900 nm is manufactured using a GaAs substrate, an AlGaAs-based material can be cited as a material system that satisfies the conditions (1) to (3) and is most easily controlled.

  However, when AlGaAs is used as the semiconductor material, Al is highly reactive and particularly has a strong bond with oxygen, so that the reliability of the LD tends to decrease.

  More specifically, when crystal growth of a semiconductor, the crystallinity of the semiconductor becomes important, but when impurities such as crystal defects and oxygen are incorporated into the semiconductor crystal, the impurities are non-radiative recombination. Become the center.

  If many non-radiative recombination centers are present in the active layer, carriers are consumed as non-radiative recombination in addition to radiative recombination that contributes to oscillation. Therefore, the efficiency with which the carriers injected into the LD are converted into light. Decreases, and high light output cannot be produced.

  In addition, since impurities such as crystal defects and oxygen serve as absorbers for LD light, absorption of light distributed in the LD increases when there are many impurities, and the emitted light The output further decreases.

  In the above semiconductor crystal, radiative recombination converts the energy of carriers into light energy, whereas non-radiative recombination converts it into thermal energy. To rise. When the temperature of the LD rises, crystal defects further grow, non-radiative recombination centers increase one after another, and problems such as deterioration of the LD occur.

  When such non-radiative recombination centers, crystal defects serving as light absorbers, impurities such as oxygen, and the like are present in the active layer of the LD, the active layer itself deteriorates.

In LD, the laser end face that emits light is formed by cleaving, and the laser end face is exposed to air when cleaved, so that the laser end face is oxidized, and the oxide formed on the laser end face is also an absorber. It becomes. When such an absorber is present on the laser end face of the LD, the laser-oscillated light is absorbed by the absorber and the temperature of the laser end face rises. Then, the band gap of the active layer near the laser end face is reduced, the light absorption amount of the active layer near the laser end face is further increased, and the positive feedback that the temperature of the laser end face further rises works, finally,
COD (optical damage) occurs on the laser end face.

  As a method for preventing the occurrence of the above problems and improving the reliability of the LD, it is conceivable to use a material containing no active Al.

  As a material that can be epitaxially grown on a GaAs substrate and does not contain Al, there is a GaInAsP-based material. In this GaInAsP-based material, the lattice constant, Eg, and refractive index can be controlled by selecting an appropriate composition.

In a material capable of lattice matching with GaAs, GaInP has the largest Eg, but this GaInP Eg corresponds to Eg of Al _0.4 Ga _0.6 As, and a material having Eg higher than that of GaInP is Al will be included.

  In the LD structure, the influence on reliability is particularly large in the quantum well active region (well layer and barrier layer sandwiching the well layer) having the highest light density. When there is a layer containing Al in the quantum well active region, there is a limit to increasing the output of the LD.

  In order to perform long-distance and high-speed spatial light transmission using an LD as a light source of the spatial light transmission system, it is necessary to further increase the output of the LD, and a more reliable LD is required.

  By configuring the quantum well active region with a material that does not contain active Al, further improvement in the reliability of the LD can be expected.

  Hereinafter, in order to improve the reliability of the LD, a material of a quantum well active region (a well layer and a barrier layer sandwiching the well layer) that does not contain Al will be considered.

  As an LD that is formed using a GaAs substrate and does not contain Al in the quantum well active region, there is an LD of 980 nm band. Generally, GaInAs (In composition about 0.2, well thickness 70-80 nm) is used as the well layer. GaAs is used as the barrier layer (see, for example, US Pat. No. 6,327,293 (Patent Document 1)).

  When an LD of 850 to 900 nm band is manufactured with the same configuration as that of a conventional LD of 980 nm band (using GaInAs for the well layer and GaAs for the barrier layer), ΔEg between the well layer and the barrier layer becomes very small. The device characteristics (threshold current, efficiency, To (temperature characteristics), etc.) are significantly deteriorated.

  Therefore, it is impossible to realize an LD in the 850 nm to 900 nm band with the conventional 980 nm band LD configuration.

  Therefore, it is conceivable to use GaInAs as the material for the well layer, and use GaInAsP as the material for the barrier layer as a material that has a sufficiently higher Eg than the well layer and does not contain Al in order to ensure reliability.

  As an LD used in a spatial light transmission system with a well layer made of GaInAs and a barrier layer made of GaInAsP, there is one described in WO 03/077389 (Patent Document 2).

  FIG. 5 shows a schematic cross-sectional view of a semiconductor laser device having a GaInAs / GaInAsP active layer oscillating at 890 nm.

5, the n-type GaAs substrate 101, n-type _Al 0.425 _{Ga 0.575} As second cladding layer having a thickness of 2.3μm is 121, 122 having a thickness of 0.2 [mu] m n-type _Al 0.5 Ga _0.5 As first cladding layer, 103 is a 0.1 μm thick n-type Al _0.4 Ga _0.6 As third light guide layer, 141 A and 141 B are 3 nm thick undoped Al _0.25 Ga _{0. 75} As the second light guide layer, 142A, undoped _in 0.1 _Ga 0.9 _{As 0.657} P _0.344 first optical guiding layer 142B has a thickness 20 nm, 105A, 105B is a thick 8nm undoped in _{0 .074} Ga _0.926 As well layer, 104 is an undoped _in 0.1 _Ga 0.9 _{As 0.657} P _0.344 barrier layer having a thickness of 5 nm, p-type Al ₀ thickness 0.1μm is 106 _.4 Ga _0.6 As third light guide layer, 107 is a p-type Al _0.5 Ga _0.5 As first cladding layer having a thickness of 0.135 μm, 108 is an undoped GaAs etching stop layer having a thickness of 3 nm, 109 Is a p-type Al _0.478 Ga _0.522 As second cladding layer having a thickness of 1.28 μm, 110 is an n-type Al _0.7 Ga _0.3 As block layer, and 112 is a p ⁺⁺ type GaAs cap layer.

  The barrier layer 104 and the well layers 105A and 105B constitute a DQW (Double Quantum Well) active layer.

When the above semiconductor laser device is manufactured, the reproducibility of element characteristics such as threshold current, efficiency, and oscillation wavelength is poor, and even the semiconductor laser device manufactured simultaneously on the wafer surface has uniform element characteristics. As a result, there was a problem that the LD operation became unstable and the LD operation became unstable.
US Pat. No. 6,327,293 International Publication No. 03/077389 Pamphlet

  The present invention solves the above problems, and provides a semiconductor laser device having an oscillation wavelength of 850 nm to 900 nm that has high reliability, excellent uniformity and reproducibility even at high output, and capable of stable operation. With the goal.

  A further object of the present invention is to provide a spatial light transmission system that solves the above-mentioned problems for spatial light transmission and that enables high-speed transmission exceeding several tens of MHz and high-speed transmission over a longer distance.

In order to achieve the above object, a semiconductor laser device of the present invention comprises:
In a semiconductor laser device having an oscillation wavelength of 850 nm to 900 nm,
A first conductivity type GaAs substrate;
A lower cladding layer of a first conductivity type formed on the GaAs substrate;
A lower guide layer of a first conductivity type formed on the lower cladding layer;
An active layer formed on the lower guide layer and having a quantum well structure;
An upper guide layer of a second conductivity type formed on the active layer;
An upper cladding layer of a second conductivity type formed on the upper guide layer,
The active layer is
Well layers,
A III-V group compound semiconductor barrier layer sandwiching the well layer and containing at least In as a group III element and at least As and P as a group V element;
It is provided between the well layer and the barrier layer on the GaAs substrate side, does not contain In as a group III element, contains an element other than In, and contains only one element as a group V element III possess a -V compound semiconductor intermediate layer,
The active layer is characterized by not containing Al .

  Here, the first conductivity type means p-type or n-type. The second conductivity type means n-type when the first conductivity type is p-type, and p-type when the first conductivity type is n-type.

  According to the semiconductor laser device having the above-described configuration, the III-V compound semiconductor barrier layer includes at least In as a group III element and at least As and P as a group V element. The active layer has this quantum well structure, so that the reliability can be improved even at high output.

  The III-V compound semiconductor intermediate layer does not contain In as a Group III element, contains an element other than In, and contains only one element as a Group V element. Even if formed, it is possible to prevent the characteristics of a plurality of semiconductor laser devices from varying, and to manufacture the semiconductor laser devices with good reproducibility. That is, the uniformity and reproducibility of the semiconductor laser device can be improved.

  Further, the III-V compound semiconductor intermediate layer does not contain In as a Group III element, contains an element other than In, and contains only one element as a Group V element, thereby stabilizing the operation of the semiconductor laser device. be able to.

  Hereinafter, the function and effect of the semiconductor laser device will be described in more detail.

[High reliability]
When the barrier layer contains at least In as the group III element and at least As and P as the group V element, the quantum well structure can be configured without containing Al, and this quantum well structure is activated. Since the active region (well layer, intermediate layer, and barrier layer) having the largest light distribution does not contain Al due to the layer, reliability is improved and high output operation is possible.

[Explanation of interface fluctuation]
In the epitaxial growth of mixed crystal semiconductors containing two or more different group V elements, it is difficult to control the composition. Furthermore, if the barrier layer contains As and P as group V elements, it is difficult to control the composition of the group V elements in the barrier layer, and if the barrier layer contains In as group III elements, In segregation occurs. To do. Therefore, when a well layer in contact with the barrier layer is formed, As, P, and In are in an unstable state at the interface between the barrier layer and the well layer, and the well layer is grown on the interface. In the interface between the barrier layer and the well layer, the group III element and the group V element fluctuate spatially, the quantum level formed in the well layer also fluctuates, and a plurality of random quantum levels are generated. Will be formed. FIG. 8A shows the energy band of the active region (well layer and barrier layer) at this time. 8A to 8D, “fluctuation” is expressed as a group of a plurality of lines.

  As described above, since it is difficult to control the interface between the barrier layer and the well layer, it is difficult to produce the quantum well structure with good reproducibility, and the distribution in the wafer plane during the production becomes large. It was.

  On the other hand, after the growth of the barrier layer, an intermediate layer that does not contain In as a group III element, contains an element other than In, and contains only one element as a group V element, and forms a well layer on the intermediate layer By doing so, it can be avoided that the quantum level is affected by the fluctuation of the interface due to In, As, and P at the interface between the well layer and the barrier layer, and a good interface can be reproduced within the wafer surface with good reproducibility. It became possible to produce uniformly.

  The quantum level can be prevented from being affected by the use of an In-free layer as an intermediate layer, so that it is not affected by In segregation at the interface directly in contact with the well layer. It is considered that the composition fluctuation at the interface between the intermediate layer and the well layer could be suppressed by configuring the V group element of the intermediate layer with one element.

[Evaluation of interface by PL (photoluminescence)]
In order to investigate the interface state between the well layer and the barrier layer, PL emission of a quantum well structure composed of a barrier layer containing In as a group III element and As and P as a group V element was confirmed. As a result, it has been found that the PL emission spectrum has a broad spectrum width (half-value width), and there are broad and relatively narrow portions in the wafer surface, and the distribution becomes large. This is presumably because the quantum level fluctuates due to fluctuations in the composition of the interface between the barrier layer and the well layer.

  On the other hand, after the growth of the barrier layer, an intermediate layer that does not contain In as a group III element, contains an element other than In, and contains only one element as a group V element, and forms a well layer on the intermediate layer As a result, the PL emission spectrum became relatively narrow, and the distribution in the wafer plane with a half width was almost eliminated, and a good quantum well interface could be formed.

  For example, a quantum well structure using a GaInAs layer as a well layer and a GaInAsP layer as a barrier layer, a GaInAs layer as a well layer, and an AlGaAs layer as a barrier layer is prepared. Then, PL emission of these quantum well structures was compared. The emission spectrum is broader in the quantum well structure having the GaInAsP barrier layer than in the quantum well structure having the AlGaAs barrier layer, and the spectrum width (half-value width) is also distributed in the quantum well structure having the AlGaAs barrier layer. Compared with, the quantum well structure having the GaInAsP barrier layer was larger. This is presumably because in the quantum well structure having the GaInAsP barrier layer, the quantum level fluctuates due to the fluctuation of the interface between the GaInAsP barrier layer and the GaInAs well layer.

  On the other hand, for example, after a GaInAsP barrier layer is grown, a GaAs intermediate layer is formed, and a GaInAs well layer is grown on the GaAs intermediate layer to produce a quantum well structure. The quantum well structure has a GaInAsP barrier layer. In spite of this, the emission spectrum of the quantum well structure was relatively narrow, and the distribution in the wafer plane with a half width was almost eliminated, and a good quantum well structure could be formed.

[Influence on LD elements]
Next, the influence of the quantum well interface on the LD device characteristics was examined.

  A barrier layer containing at least In as a group III element and at least As and P as a group V element, and a well layer in contact with the barrier layer, and there is another layer between the barrier layer and the well layer When a non-existing LD was produced, the LD's oscillation spectrum had a plurality of random spectra before and after the peak wavelength of the main oscillation spectrum, leading to an increase in threshold current and a decrease in efficiency. Became unstable.

  This is because the fluctuation of the composition of the interface between the well layer and the barrier layer becomes large, the quantum level fluctuates, the width of the EL spectrum until oscillation is widened, and a plurality of random quantum levels are formed. For this reason, carriers injected into the well layer do not fall within a single level, and if a large number of carriers are not injected before oscillation, gain for oscillation cannot be gained, and the threshold current increases. Conceivable.

  In addition, since a plurality of random quantum levels are formed, there are a plurality of levels that can oscillate when carriers are injected, and the oscillation wavelength cannot be controlled. Sometimes the oscillation wavelength shifts 10 nm or more from the set wavelength, the oscillation wavelength jumps to another quantum level due to temperature change, and there are multiple random spectra around the peak wavelength of the main oscillation spectrum, etc. LD operation has become unstable.

  Therefore, the above-mentioned LD is very difficult to control the wavelength, and is not suitable for use as a light source for spatial light transmission that requires the wavelength to be precisely matched.

  In addition, since the operation of the LD becomes unstable, if the LD is used as a spatial light transmission light source and driven at a high frequency, a dynamic characteristic defect occurs.

  On the other hand, after the growth of the barrier layer, an intermediate layer that does not contain In as a group III element, contains an element other than In, and contains only one element as a group V element, and forms a well layer on the intermediate layer When the LD was manufactured, the oscillation spectrum of the LD became a single peak, device characteristics such as threshold current and efficiency were improved, the oscillation wavelength could be strictly controlled, and at high temperatures and high frequency driving Even at times, it became possible to operate the LD stably.

[Oscillation wavelength]
Here, an LD element having a wavelength shorter than 850 nm was also examined. In the wavelength band shorter than 850 nm, the Eg of the intermediate layer cannot be an intermediate Eg between the well layer and the barrier layer. For example, when the intermediate layer is formed of GaAs, the Eg of the intermediate layer becomes smaller than the Eg of the well layer. In this case, since the well layer feels the interface between the barrier layer and the intermediate layer as a barrier as a quantum well, there is almost no effect of forming the intermediate layer.

  Further, for example, when the intermediate layer is formed of GaP, the Eg of the intermediate layer becomes larger than the Eg of the barrier layer, and the intermediate layer has a lattice constant greatly different from that of the GaAs substrate. When such a layer having greatly different lattice constants is present, the crystallinity is lowered, and the element characteristics such as threshold current and efficiency are deteriorated as well as the reliability of the LD element. In addition, the same effect as when the oscillation wavelength is not less than 850 nm and not more than 900 nm can be obtained by using an intermediate layer that does not contain In as a group III element but contains an element other than In and contains only one element as a group V element. Was not obtained.

In the semiconductor laser device of one embodiment,
The III-V compound semiconductor intermediate layer is made of GaAs.

  According to the semiconductor laser device of the above embodiment, the GaAs does not include In as a group III element, includes an element other than In, and includes only one element as a group V element. There is an effect of suppressing the influence of the composition fluctuation of the interface.

  In addition, in the semiconductor laser device, by forming the intermediate layer from GaAs, the intermediate layer can be made to have an intermediate Eg between the Eg of the well layer and the Eg of the barrier layer.

  If the Eg of the intermediate layer becomes smaller than the Eg of the well layer, the well layer feels the interface between the barrier layer and the intermediate layer as a barrier as a quantum well. Not.

  Further, if the Eg of the intermediate layer becomes larger than the Eg of the barrier layer, it becomes difficult for carriers to be injected into the well layer, and device characteristics such as threshold current and efficiency are deteriorated.

  Also, if the lattice constant of the intermediate layer is significantly different from the lattice constant of the substrate, a layer having a lattice constant greatly different from that of the substrate is present in the vicinity of the active layer, and the crystallinity of the active layer is reduced. In addition to degradation of device characteristics such as threshold current and efficiency, reliability is also degraded.

  Therefore, it can be said that GaAs is most suitable as the intermediate layer in the semiconductor laser device.

In the semiconductor laser device of one embodiment,
The thickness of the III-V compound semiconductor intermediate layer is 0.5 nm or more and 2 nm or less.

  According to the semiconductor laser device of the above embodiment, the semiconductor laser device was manufactured by changing the thickness of the intermediate layer, and the effect of changing the thickness of the intermediate layer was investigated.

  As a result, it was found that when the thickness of the intermediate layer was 0.5 nm or more and 2 nm or less, device characteristics such as threshold current, efficiency, and To were the best.

  When the intermediate layer thickness is thin, the well layer feels as a barrier of the quantum well as a whole of the barrier layer and the intermediate layer, and when the intermediate layer layer thickness is less than 0.5 nm, the intermediate layer is formed, Since the influence of the composition fluctuation due to the barrier layer appears and the quantum level fluctuates, the thickness of the intermediate layer needs to be 0.5 nm or more in order to avoid the influence of the composition fluctuation due to the barrier layer.

  Further, in the semiconductor laser device, the Eg of the intermediate layer can be an intermediate Eg between the Eg of the well layer and the Eg of the barrier layer. In this case, since ΔEg between the well layer and the intermediate layer becomes small, if the thickness of the intermediate layer is increased, the quantum level of the intermediate layer decreases, approaches the quantum level of the well layer, and approaches the quantum level of the well layer. Since the accumulated carriers easily overflow into the carriers in the intermediate layer, the threshold current increases, the efficiency decreases, and the temperature characteristics deteriorate. For this reason, the intermediate layer thickness needs to be 2 nm or less. Here, FIG. 8B shows an energy band diagram of the quantum well structure when the intermediate layer is thin, and FIG. 8C shows an energy band diagram of the quantum well structure when the intermediate layer is thick.

  For example, when the thickness of the GaAs intermediate layer is increased, it is necessary to reduce the barrier layer or increase the interval between the well layer and the well layer. If the barrier layer is thin, the thin barrier layer will not function as a barrier layer. If the interval between the well layer and the well layer in the MQW structure is too wide, carriers cannot be uniformly injected into each well layer. Will fall.

In the semiconductor laser device of one embodiment,
The III-V compound semiconductor barrier layer is made of GaInAsP,
The well layer is made of GaInAs;
The ratio of In in the group III element of the III-V compound semiconductor barrier layer is larger than the ratio of In in the group III element of the well layer,
The well width of the well layer is 6 nm or less.

  According to the semiconductor laser device of the above embodiment, the threshold current decreases when the well width of the well layer is 6 nm or less compared to when the well width of the well layer exceeds 6 nm. Efficiency is increased and higher output is possible.

[Explanation of high output]
In order to achieve a high output in a semiconductor laser device, it is important to make the laser beam shine by injecting fewer carriers and to reduce the absorption of oscillation light. That is, it is desired that the threshold current is low and the efficiency is high. Further, when the amount of injected carriers and the absorption of oscillation light increase, the LD chip temperature rises, causing deterioration, and it becomes difficult to further increase the output of the semiconductor laser device. For this reason, high reliability is required to increase the output of the semiconductor laser device.

  A quantum well structure is suitable as the structure of the active layer of a high-power semiconductor laser device. The thinner the well width, the more efficiently it is converted into light with fewer carriers due to the quantum effect, and the threshold current is reduced. Lowers and improves efficiency. However, if the well width is too thin, gain saturation will occur.

  Considering the same oscillation wavelength, if the well width is reduced, the Eg of the well layer needs to be reduced. In a semiconductor laser device in the 850 nm to 900 nm band, if a well layer having In is used and the composition of In is increased, the Eg of the well layer can be reduced. When the In in the well layer is increased, the amount of strain increases, the effective mass of carriers decreases, the threshold current decreases, and the efficiency increases.

  Therefore, from the viewpoint of higher output, it is desirable to increase the In composition of the well layer and reduce the well width. Specifically, the well width is preferably 4 nm or more and 6 nm or less.

[Reliability issues]
Because of the high output, the reliability tends to decrease when the well width of the quantum well active layer is reduced. This is because the light intensity (light density) per unit volume increases as the volume of the well layer decreases, so even if absorbers exist at the same density in the well layer or at the emission end face, the absorber It is considered that the intensity of the light that is felt increases and the amount of absorption increases, resulting in a decrease in reliability.

[Effect of reliability]
In the 850 to 900 nm band, GaInAs can be used as a material for the well layer, and GaInAsP can be used as the material for the barrier layer as a material that has a sufficiently higher Eg than the well layer and does not contain Al.

  By using a GaInAs layer as a well layer and a GaInAsP layer as a barrier layer, high reliability can be maintained at high output even when the well width is thin. This is presumably because COD is less likely to occur because the quantum well active region with the highest light density does not contain active Al. In addition, it becomes difficult for impurities such as oxygen to be taken into the well layer, and since the propagation of crystal defects in the active layer is suppressed by In of the well layer and the barrier layer, deterioration of the active layer itself is also suppressed, Reliability is considered to be improved.

  Therefore, for the high output and high reliability of the semiconductor laser device, it is preferable that the well layer is made of GaInAs and the barrier layer is made of GaInAsP, and the well width is narrowed, but the barrier layer is made of GaInAsP. In this case, fluctuations in the composition due to In, As, and P occur at the barrier layer interface, and a good quantum well interface cannot be obtained. In addition, the thinner the well width, the greater the influence. As a result, a good quantum well structure cannot be obtained.

  Further, when the In composition of the GaInAsP barrier layer is small, in order to increase ΔEg between the barrier layer and the well layer, it is necessary to increase the P composition of the barrier layer. However, if the P composition is increased, The difference in lattice constant from the GaAs substrate increases, and the crystallinity of the barrier layer decreases.

  Further, if the In composition of the GaInAsP barrier layer is made larger than the In composition of the GaInAs well layer, even if the lattice constant difference between the barrier layer and the GaAs substrate is relatively small, ΔEg between the barrier layer and the well layer is relatively large. can do.

  Therefore, the In composition of the GaInAsP barrier layer is desirably larger than the In composition of the GaInAs well layer.

  However, it has been found that when the ratio of In in the group III element of the barrier layer is larger than the ratio of In in the group III element of the well layer, the fluctuation of the composition at the barrier interface is particularly increased. This is because the segregation of In occurs on the surface of the barrier layer during the growth of the well layer, so when growing a layer having a smaller In ratio than the barrier layer, the effect of the segregation of In on the surface of the barrier layer is affected. It can be considered that it has received a lot.

  In addition, the influence of the composition fluctuation at the interface between the well layer and the barrier layer greatly affects element characteristics such as the oscillation wavelength and threshold current of the semiconductor laser device. In order to achieve high output and high reliability of the semiconductor laser device, it is desirable to narrow the well width. However, in the conventional GaInAs / GaInAsP quantum well structure, the smaller the well width, the greater the influence of the interface. On the contrary, the device characteristics are deteriorated.

  As described above, in the conventional GaInAs / GaInAsP quantum well active layer, it is possible to realize a highly reliable semiconductor laser device of 850 to 900 nm, but it is difficult to reduce the well width. In addition, it is a particularly serious problem when the proportion of In in the group III element of the barrier layer is larger than the proportion of In in the group III element of the well layer.

  After forming the GaInAsP barrier layer, by forming an intermediate layer that does not contain In as a group III element, contains an element other than In, and contains only one element as a group V, the In of the group III element of the barrier layer Even when the ratio is larger than the ratio of In in the group III element of the well layer, the influence of interface fluctuation due to In, As, and P at the GaInAsP barrier interface is avoided despite the small well width. Since a good interface can be obtained, a semiconductor laser capable of high reliability and stable operation even at high output is possible.

In the semiconductor laser device of one embodiment,
The well width of the well layer is 4 nm or more.

  According to the semiconductor laser device of the above embodiment, it is possible to prevent the characteristics from being deteriorated because the well width of the well layer is 4 nm or more.

In the semiconductor laser device of one embodiment,
The guide layer is made of Al _x Ga _1-x As (x ≧ 0.3).

According to the semiconductor laser device of the above embodiment, the guide layer is made of Al _x Ga _1-x As (x ≧ 0.3), so that high output and low power consumption can be achieved.

[Explanation of high output and low power consumption]
In a conventional semiconductor laser device having an oscillation wavelength of 850 nm or more and 900 nm or less, a tensile strained GaInAsP composition region is used as a barrier layer in order to increase ΔEg with the GaInAs well layer. In this barrier layer, if the product of the strain amount and the layer thickness becomes too large, crystal defects are generated during growth, and device characteristics such as threshold current, efficiency, and reliability are significantly deteriorated.

  Therefore, the GaInAsP barrier layer cannot be made too thick. Further, when a GaInAsP barrier layer is used, it is difficult to obtain ΔEc between the barrier layer and the well layer. For this reason, if the GaInAsP barrier layer is made too thick, carrier leakage to the barrier layer increases and To deteriorates. Thus, when the GaInAsP barrier layer is used, the thickness of the barrier layer cannot be increased, but by providing guide layers on both sides of the quantum well active layer separately from the barrier layer, optical It became possible to control the confinement.

  As the material of the guide layer, GaInP containing no Al is conceivable. In this case, since Al is not used, it seems that the reliability is improved at first glance, but it has been found that the reliability at the time of high output is actually worse. This is because when the GaInP guide layer is used, the threshold current increases, the efficiency decreases, the device resistance increases, a large current and voltage are required to produce the same light output, and the power consumption increases. This is presumed to be due to a vicious circle in which the device temperature rises and ΔEc between the barrier layer and the well layer is small and To is bad, and the threshold current further rises due to the rise in device temperature.

  As described above, when the GaInP guide layer is used, the efficiency is lowered and the operating voltage is increased because the valence band discontinuity between the guide layer and the active layer is large, and the GaInP guide layer is a large barrier against holes. This is probably because the hole injection efficiency has decreased.

  On the other hand, when an AlGaAs guide layer is used, the efficiency is increased, the element resistance is lowered, and high output and low power consumption are possible.

  In addition, by using an AlGaAs guide layer, To is improved and stable operation is performed at a high temperature. This is because the difference in the conduction band between the guide layer and the active layer becomes larger when the AlGaAs guide layer is used than when the GaInP layer guide layer is used, and carriers overflowing from the cladding layer to the barrier layer are guided. It is thought that it stayed in the quantum well without leaking into the layer. This AlGaAs guide layer had an effect of ensuring To at an Al composition of 0.3 or more.

  Furthermore, the AlGaAs guide layer also improves the reliability over the GaInP guide. Since the AlGaAs guide layer contains Al, it is easy to bond with oxygen. However, in the guide layer, since the light distribution is smaller than that of the active layer, the influence of the bond with oxygen is small. Reliability was not significantly affected.

The manufacturing method of the semiconductor laser device of the present invention includes:
A method of manufacturing a semiconductor laser device for manufacturing the semiconductor laser device,
After forming the III-V compound semiconductor barrier layer and before forming the well layer, the III-V compound semiconductor intermediate layer is formed by MOCVD.

  According to the method for manufacturing a semiconductor laser device having the above-described structure, the III-V compound semiconductor barrier layer includes at least In as a group III element and at least As and P as a group V element. The structure can be configured without containing Al, and the active layer has this quantum well structure, so that the reliability can be improved even at high output.

  The III-V compound semiconductor intermediate layer does not contain In as a Group III element, contains an element other than In, and contains only one element as a Group V element. Even if formed, it is possible to prevent the characteristics of a plurality of semiconductor laser devices from varying, and to manufacture the semiconductor laser devices with good reproducibility. That is, the uniformity and reproducibility of the semiconductor laser device can be improved.

  Further, the III-V compound semiconductor intermediate layer does not contain In as a Group III element, contains an element other than In, and contains only one element as a Group V element, thereby stabilizing the operation of the semiconductor laser device. be able to.

  Further, since the intermediate layer is formed by the MOCVD method, the mass productivity of the semiconductor laser device can be improved.

  In MOCVD growth, the vapor pressures of the group V elements As and P are different from each other. Therefore, when the barrier layer contains As and P, the surface after the barrier layer growth is particularly unstable, and the interface is particularly controlled. Although difficult, the interface can be easily controlled by forming the intermediate layer.

The spatial light transmission system of the present invention is
The semiconductor laser device is provided.

  According to the spatial light transmission system having the above configuration, high-speed spatial light transmission exceeding several tens to a hundred Mbps can be realized by using the semiconductor laser device.

[Explanation of high-speed spatial light transmission]
When an LD is used as a light source for spatial light transmission, it is necessary to precisely match the wavelength. With a conventional GaInAs / GaInAsP active layer LD, it is very difficult to control the wavelength.

  Further, in the LD of the GaInAs / GaInAsP active layer, since the steepness of the interface is poor, the oscillation spectrum does not have a single peak, and when used for spatial light transmission, it causes a dynamic characteristic failure when driving at a high frequency.

  On the other hand, by using the semiconductor laser device of the present invention for a spatial light transmission system, it is highly reliable even at high output, and the oscillation wavelength is not less than 850 nm and not more than 900 nm. Therefore, the wavelength can be strictly controlled, and good dynamic characteristics can be obtained even when driving at a high frequency, and it can be used as a light source for spatial light transmission.

  According to the semiconductor laser device of the present invention, the III-V compound semiconductor barrier layer includes at least In as the group III element and at least As and P as the group V element, thereby forming the quantum well structure from Al. It is possible to configure without including the quantum well structure, and by having the quantum well structure in the active layer, reliability can be improved even at high output.

  Further, the group III-V compound semiconductor intermediate layer does not contain In as a group III element, contains an element other than In, and contains only one element as a group V element. Even if formed, it is possible to prevent the characteristics of a plurality of semiconductor laser devices from varying, and to manufacture the semiconductor laser devices with good reproducibility. That is, the uniformity and reproducibility of the semiconductor laser device can be improved.

  Further, the III-V compound semiconductor intermediate layer does not contain In as a Group III element, contains an element other than In, and contains only one element as a Group V element, thereby stabilizing the operation of the semiconductor laser device. be able to.

  According to the method for manufacturing a semiconductor laser device of the present invention, the III-V compound semiconductor barrier layer includes at least In as a group III element and at least As and P as a group V element, thereby providing a quantum well structure. Can be configured without containing Al, and the active layer has this quantum well structure, so that the reliability can be improved even at high output.

  Further, the group III-V compound semiconductor intermediate layer does not contain In as a group III element, contains an element other than In, and contains only one element as a group V element. Even if formed, it is possible to prevent the characteristics of a plurality of semiconductor laser devices from varying, and to manufacture the semiconductor laser devices with good reproducibility. That is, the uniformity and reproducibility of the semiconductor laser device can be improved.

  Further, the III-V compound semiconductor intermediate layer does not contain In as a Group III element, contains an element other than In, and contains only one element as a Group V element, thereby stabilizing the operation of the semiconductor laser device. be able to.

  Further, since the intermediate layer is formed by the MOCVD method, the mass productivity of the semiconductor laser device can be improved.

  According to the spatial light transmission system of the present invention, since the semiconductor laser device is used, high-speed spatial light transmission exceeding several tens to a hundred Mbps can be realized.

[First Embodiment]
FIG. 1 is a schematic cross-sectional view of the semiconductor laser device according to the first embodiment of the present invention. This semiconductor laser device is an example of a semiconductor laser device for spatial light transmission using a GaInAsP layer as a barrier layer.

In FIG. 1, 1 is an n-type GaAs substrate, 2 is an n-type Al _0.5 Ga _0.5 As cladding layer having a thickness of 1.8 μm, and 3 is an n-type Al _0.4 Ga _{0. 6} As guide layer, 4A, 4C are 20 nm thick undoped In _0.2 Ga _0.8 As _0.45 P _0.55 barrier layer, 4B is 5 nm thick undoped In _0.2 Ga _0.8 As _{0 .45} P _0.55 barrier layer, 5A, 5B are 4.6 nm thick undoped In _0.07 Ga _0.93 As well layer, 6 is 0.1 μm thick p-type Al _0.4 Ga _0.6 As guide layer, 7 is a p-type Al _0.5 Ga _0.5 As first cladding layer having a thickness of 0.15 μm, 8 is a p-type GaAs etching stop layer having a thickness of 4 nm, and 9 is a p-type having a thickness of 1.28 μm. type _{Al 0.5 Ga} 0.5 As second cladding layer, 10 thickness N-type _Al 0.7 _{Ga 0.3} As blocking layer of 0.6 .mu.m, n-type GaAs block layer having a thickness of 0.3μm is 11, 12 p-type GaAs cap layer having a thickness of about 4 [mu] m, 13A is AuZn / Au Electrode, 13B is an AuGe / Ni / Au electrode, and 14A and 14B are undoped GaAs intermediate layers having a thickness of 1.5 nm.

The n-type GaAs substrate 1 is an example of a first conductivity type GaAs substrate, the n-type Al _0.5 Ga _0.5 As cladding layer 2 is an example of a first conductivity type lower cladding layer, and an n-type Al ₀ layer. _.4 Ga _0.6 As guide layer 3 is an example of the lower guide layer of the first conductivity type, and In _0.2 Ga _0.8 As _0.45 P _0.55 barrier layers 4A, 4B, and 4C are III-V groups. An example of a compound semiconductor barrier layer, undoped In _0.07 Ga _0.93 As well layers 5A and 5B are examples of well layers, and p-type Al _0.4 Ga _0.6 As guide layer 6 is an upper guide of the second conductivity type. An example of the layer, the p-type Al _0.5 Ga _0.5 As first cladding layer 7 is an example of the second conductivity type upper cladding layer, and the undoped GaAs intermediate layers 14A and 14B are examples of the III-V group compound semiconductor intermediate layer. It is.

  The barrier layers 4A, 4B, 4C, the well layers 5A, 5B, and the intermediate layers 14A, 14B constitute a quantum well active layer 16 having a DQW structure. The quantum well active layer 16 is an example of an active layer.

  The intermediate layer 14A is disposed between the barrier layer 4A and the well layer 5A. The intermediate layer 14B is disposed between the barrier layer 4B and the well layer 5B.

  Hereinafter, the manufacturing method of the semiconductor laser device of the first embodiment will be described with reference to FIGS. 2A to 2F.

First, as shown in FIG. 2A, an n-type Al _0.5 Ga _0.5 As cladding layer 2 having a thickness of 1.8 μm and an n-type Al _0.4 layer having a thickness of 0.1 μm are formed on an n-type GaAs substrate 1. 3. Ga _0.6 As guide layer 3, undoped In _0.2 Ga _0.8 As _0.45 P _0.55 barrier layer 4 A having a thickness of 20 nm, undoped GaAs intermediate layer 14 A having a thickness of 1.5 nm, thickness 4. 6 nm undoped In _0.07 Ga _0.93 As well layer 5 A, 5 nm thick undoped In _0.2 Ga _0.8 As _0.45 P _0.55 barrier layer 4 B, 1.5 nm thick undoped GaAs intermediate Layer 14B, 4.6 nm thick undoped In _0.07 Ga _0.93 As well layer 5B, 20 nm thick undoped In _0.2 Ga _0.8 As _0.45 P _0.55 barrier layer 4C, thickness 0.1 μm P-type Al _0.4 Ga _0.6 As guide layer 6, p-type Al _0.5 Ga _0.5 As first cladding layer 7 having a thickness of 0.15 μm, 4 nm p-type GaAs etching stop layer 8, thickness A p-type Al _0.5 Ga _0.5 As second clad layer 9 having a thickness of 1.28 μm and a p-type GaAs cap layer 12a having a thickness of 0.75 μm are first crystallized by MOCVD (metal organic chemical vapor deposition). Sequentially formed with growth.

In the first crystal growth, the raw materials of Ga, Al, In, As, and P are TMG (trimethyl gallium), TMA (trimethyl aluminum), TMI (trimethyl indium), AsH ₃ (arsine), and PH ₃ (phosphine), respectively. And n-type SiH ₄ (monosilane) and p-type DEZ (diethylzinc).

Next, a 6 μm wide resist mask (not shown) is formed on the p-type GaAs cap layer 12a by a normal photolithography technique, and the p-type GaAs cap layer 12a and p-type Al ₀ not covered with the mask are formed. _.5 Ga _0.5 As second clad layer 9 is removed by etching to form p-type GaAs cap layer 12a and p-type Al _0.5 Ga _0.5 As second clad layer 9 as shown in FIG. 2B. A striped ridge is formed.

When the ridge is formed, an etchant having high selectivity is used for the p-type Al _0.5 Ga _0.5 As second cladding layer 9 and the p-type GaAs etching stop layer 8. Etching is stopped and the ridge width is controlled. In the first embodiment, the etching is adjusted so that the width of the bottom of the ridge is 2.7 μm.

Next, after removing the resist mask on the ridge, as shown in FIG. 2C, an n-type Al _0.7 Ga _0.3 As block layer 10 having a thickness of 0.6 μm and an n-type having a thickness of 0.3 μm. A GaAs block layer 11 and a p-type GaAs cap layer 12b having a thickness of 1.05 μm are sequentially formed by second crystal growth by MOCVD.

  When the second crystal growth is performed, the crystal growth proceeds in a region on both sides of the ridge and a region on the ridge, and a growth film is formed in the shape of a mountain-shaped protrusion on the ridge.

  Next, a resist is applied on the entire surface of the p-type GaAs cap layer 12b, exposed on the entire surface, and adjusted for development time, thereby removing the resist until the chevron-shaped protrusion on the ridge appears. That is, the resist on the ridge is removed, and the resist outside the ridge remains. Etching is performed in this state, and a growth layer formed on the ridge by the second crystal growth and a part (about 0.05 μm) of the p-type GaAs cap layer 12a formed by the first crystal growth. When is removed, the state shown in FIG. 2D is obtained.

Next, the resist is removed, and as shown in FIG. 2E, a 4 μm p-type GaAs cap layer 12c is formed by third crystal growth by MOCVD. At this time, the impurity is doped at a density of 1 × 10 ²⁰ cm ⁻³ so that only the uppermost layer of 0.3 μm can easily make contact with the electrode.

  Next, the wafer having the laminated structure of FIG. 2E is polished to a thickness of 100 μm, and as shown in FIG. 2F, an AuZn / Au electrode 13A is formed by vapor deposition on the p side, and an AuGe / Ni / Au electrode is formed on the n side. 13B is formed by vapor deposition. That is, the AuZn / Au electrode 13A is electrically connected to the p-type GaAs cap layer 12, and the AuGe / Ni / Au electrode 13B is electrically connected to the n-type GaAs substrate 1. The p-type GaAs cap layer 12 includes a p-type GaAs cap layer 12a formed by the first crystal growth, a p-type GaAs cap layer 12b formed by the second crystal growth, and a third crystal growth. The p-type GaAs cap layer 12c is formed.

Next, the wafer having the structure of FIG. 2F is cleaved to form a plurality of laser bars having a width of 500 μm, and then an Si film and an Al ₂ O ₃ film are formed on one end face of each laser bar so that the reflectance is 5%. Is formed by vapor deposition, and an Si film and an Al ₂ O ₃ film are formed on the other end face of each laser bar by vapor deposition so that the reflectance is 90%. One end surface of the laser bar and the other end surface of the laser bar are formed to be perpendicular to the extending direction of the ridge.

  Finally, each laser bar is divided to obtain a semiconductor laser device in a chip state.

  When the semiconductor laser device thus fabricated was mounted on a stem and a pulse current having a duty of 50% was applied to the semiconductor laser device, the semiconductor laser device oscillated at an oscillation wavelength of 869 nm (25 ° C.). In the semiconductor laser device, the oscillation threshold current was 18.4 mA and the efficiency was 1 W / A.

  When the current supplied to the semiconductor laser device was increased, the semiconductor laser device oscillated without causing COD up to an output of 500 mW.

  In the semiconductor laser device, To = 150K and RIN = −120 dB / Hz, good characteristics such as high characteristic temperature and low noise were obtained.

  Further, the semiconductor laser device obtained a good output waveform even when driven at a high frequency.

  In the semiconductor laser device having the above configuration, by setting the well width of the well layers 5A and 5B to 6 nm or less, the threshold current is reduced, the efficiency is increased, and the output can be increased. However, when the well width is thinner than 4 nm, the characteristics are worsened.

  Further, by configuring the barrier layers 4A, 4B, and 4C with GaInAsP, it was possible to secure high reliability even though the well width was narrowed and the optical density of the quantum well active layer 16 was increased. . This is because the quantum well structure of the quantum well active layer 16 does not contain active Al, and as a result, the non-radiative recombination centers and the oxygen as the absorber are reduced in the quantum well active layer 16 and at the end face. The reliability is considered to have improved.

  In the conventional technique, it is very difficult to control the composition of GaInAsP, and in-plane uniformity and reproducibility are difficult. In the active layer using GaInAs for the well layer and using the GaInAsP layer for the barrier layer, it is very difficult to control the interface between the GaInAsP layer and the GaInAs layer. In particular, if the well width is reduced, the interface is easily affected, and if a good interface cannot be obtained, it is greatly affected.

  In addition, when the in-plane distribution becomes large or the reproducibility becomes poor, the production yield decreases and the cost increases.

  Further, the interface between the well layer and the barrier layer greatly affects device characteristics such as an oscillation wavelength and a threshold current due to its steepness. In a conventional GaInAs / GaInAsP active layer LD, device characteristics such as threshold current are deteriorated, and device characteristics such as threshold current and oscillation wavelength are deteriorated in distribution and reproducibility so that the device characteristics are uniform. It has been found that not only is it very difficult to control, but also the LD operation becomes unstable depending on the operating conditions (temperature, high frequency driving, etc.).

  In contrast, in the first embodiment, a GaAs intermediate layer 14A is formed between the InGaAsP barrier layer 4A and the InGaAs well layer 5A, and an undoped GaAs intermediate is formed between the InGaAsP barrier layer 4B and the InGaAs well layer 5B. Layer 14B is formed. That is, the interface between the GaInAsP layer and the GaInAs layer is eliminated.

  The composition of the epitaxial growth of the GaAs intermediate layers 14A and 14B can be easily controlled. Instead of the GaAs intermediate layers 14A and 14B, if a mixed crystal semiconductor in which the group V is composed of two or more elements is to be epitaxially grown, it is difficult to control the composition in the epitaxial growth.

  Further, after the growth of the barrier layers 4A and 4B containing As and P as a group V element and In as a group III element, the group III element does not contain In but contains an element other than In, and a group V By growing the intermediate layers 14A and 14B containing only one element as an element and growing the well layers 5A and 5B on the intermediate layers 14A and 14B, the influence of fluctuation at the interface between the barrier layers 4A and 4B is avoided. As a result, a good interface can be produced uniformly with good reproducibility within the wafer surface. This is because the use of a layer containing no In as the intermediate layers 14A and 14B eliminates the influence of In segregation at the interface directly in contact with the well layers 5A and 5B, and further includes an intermediate layer 14A containing only one element as a group V element. , 14B, it is considered that the fluctuation of the composition due to As, P at the interface in contact with the well layers 5A, 5B could be suppressed.

  Further, since the fluctuation of the quantum level of the well layers 5A and 5B is suppressed, the oscillation spectrum of the semiconductor laser device becomes a single peak, the device characteristics such as threshold current and efficiency are improved, and the oscillation wavelength is strictly set. In addition, it is possible to stabilize the operation of the semiconductor laser device even at high temperatures and high frequency driving.

  As described above, the first embodiment is an example using a GaInAsP layer as a barrier layer, a GaInAs layer as a well layer, and a GaAs layer as an intermediate layer. GaInAsP barrier layers 4A and 4B and a GaInAs well layer 5A are used. , 5B are formed between the GaInAsP barrier layers 4A, 4B and the GaInAs well layers 5A, 5B so that the quantum levels of the well layers 5A, 5B are GaInAsP barrier layers 4A. , 4B is not affected by interface fluctuations, and even if the well width of the GaInAs well layers 5A, 5B is narrowed, the in-plane distribution and reproducibility of the characteristics are remarkably higher than when the GaAs intermediate layers 14A, 14B are not included. Can be improved.

  For comparison, the LD of Comparative Example 1 in which the barrier layers 4A, 4B, and 4C are changed to AlGaAs barrier layers in the first embodiment and the LD of Comparative Example 2 in which no GaAs intermediate layer is formed in the first embodiment. And were produced respectively. When comparing the oscillation spectrum of the LD with respect to the comparative examples 1 and 2, the LD of the comparative example 1 has a unimodal spectrum, but the LD of the comparative example 2 has a plurality of peaks before and after the peak wavelength of the main oscillation spectrum. There was a random spectrum, leading to an increase in threshold current and a decrease in efficiency, and the LD operation became unstable.

  In the LD of Comparative Example 2 described above, the fluctuation of the interface between the well layer and the barrier layer becomes large, the quantum level of the well layer fluctuates, the width of the EL spectrum until oscillation increases, and the quantum level of the well layer also increases. Because the position is fluctuating, the injected carriers do not fit in one level, and unless many carriers are injected before oscillation, gain for oscillation cannot be gained, and the threshold current increases. .

  Further, in the LD of Comparative Example 2, since the quantum level of the well layer is fluctuating, the oscillation level cannot be specified when carriers are injected, and the oscillation wavelength cannot be controlled. In some cases, the LD operation is unstable, for example, the oscillation wavelength shifts by more than 10 nm from the set wavelength, the oscillation wavelength jumps due to temperature changes, and there are multiple random spectra around the peak wavelength of the main oscillation spectrum. Became.

  Thus, the LD of Comparative Example 2 in which the oscillation wavelength cannot be controlled cannot be used as a spatial light transmission light source that requires the oscillation wavelength to be strictly adjusted.

  Further, since the LD of Comparative Example 2 is unstable in operation, the oscillation spectrum does not become unimodal. This is a cause of poor dynamic characteristics in high-frequency driving when the LD of Comparative Example 2 is used as a spatial light transmission light source.

  On the other hand, in the semiconductor laser device of the first embodiment, the GaAs intermediate layers 14A and 14B are formed after the growth of the GaInAsP barrier layers 4A and 4B, and the GaInAs well layers 5A and 5B are formed on the GaAs intermediate layers 14A and 14B. Since 5B is grown, the oscillation spectrum is unimodal, device characteristics such as threshold current and efficiency are improved, and the oscillation wavelength can be strictly controlled. Even became able to operate stably.

  FIG. 7 shows a plot of the threshold current and the slope efficiency for the GaAs intermediate layer by fabricating an LD element with a different thickness of the GaAs intermediate layer formed between the GaInAs well layer and the GaInAsP barrier layer.

  FIG. 7 shows that the formation of the GaAs intermediate layer reduces the threshold current and improves the efficiency. This is because the presence of the GaAs intermediate layer between the GaInAs well layer and the GaInAsP barrier layer is affected by the fluctuation of the interface due to the interaction of In, As, and P of the GaInAsP barrier layer at the interface of the GaInAsP barrier layer. It is thought that it was gone.

  Further, when the thickness of the GaAs intermediate layer exceeded 2 nm, the threshold current increased and the efficiency decreased. Since ΔEg between the GaInAs well layer and the GaAs intermediate layer is relatively small, when the GaAs intermediate layer is thickened, the level that can be formed in the GaAs intermediate layer is lowered, and carriers easily leak from the GaInAs well layer to the GaAs intermediate layer. It is considered that carriers are not efficiently confined in the GaInAs well layer, Ith (threshold current) is increased, and efficiency is lowered (FIG. 8C).

  In the first embodiment, the oscillation wavelength is approximately 870 nm. In the GaInAs well layer / GaInAsP barrier quantum well active layer having an oscillation wavelength of 850 nm to 900 nm, the thickness of the GaAs intermediate layer is 0.5 nm to 2 nm. Ith decreased and efficiency improved.

  FIG. 6 shows the relationship between the layer thickness and To when the LD is manufactured by changing the layer thickness of the GaAs intermediate layer. A curve A in FIG. 6 shows the above relationship when a GaAs intermediate layer is formed between the well layer and the barrier layer located closer to the substrate than the well layer. A curve B in FIG. 6 indicates that a GaAs intermediate layer is formed between the well layer and the barrier layer located on the substrate side of the well layer, and the barrier layer is separated from the well layer and the substrate from the well layer. The above relationship is shown when a GaAs intermediate layer is formed between the layers.

  As can be seen from FIG. 6, it has been found that the To decreases as the thickness of the GaAs intermediate layer increases. In order to obtain sufficient To, the GaAs intermediate layer needs to be 2 nm or less. The reason why To decreases when the GaAs intermediate layer is thickened is that the quantum level formed in the GaAs intermediate layer decreases as the GaAs intermediate layer is thickened, and carriers are more likely to leak from the well layer (see FIG. Comparison between 8B and FIG. 8C).

  It was possible to suppress the decrease in To when the GaAs layer was put on only one side than on both sides. This is presumably because electrons injected from the substrate side are prevented from leaking to the quantum level formed in the GaAs layer (comparison between FIG. 8B and FIG. 8D).

  Here, a GaAs layer is used as an intermediate layer formed between the well layer and the barrier layer. However, the layer that can be used as the intermediate layer is not limited to the GaAs layer, and does not include In as a group III element. Any other layer may be used as long as it includes other elements and includes only one element as a group V element.

  In the first embodiment, the GaInAsP layer is used as the barrier layer. However, the barrier layer is not limited to the GaInAsP layer, and the barrier layer includes at least In in group III and at least As and P as group V. Then, the same effect as the case where the GaInAsP layer is used as the barrier layer can be obtained.

  In the first embodiment, the oscillation wavelength is approximately 870 nm, and a tensile strained GaInAsP composition region is used as a barrier layer in order to obtain ΔEg for the well layer. If the product of the strain amount and the layer thickness becomes too large, crystal defects are generated during growth, and device characteristics such as threshold current, efficiency, and reliability are significantly deteriorated.

  Therefore, the GaInAsP layer used as the barrier layer cannot be made too thick. Further, when the GaInAsP layer is used as a barrier layer, it is difficult to obtain ΔEc between the GaInAsP layer and the well layer. Therefore, if the GaInAsP layer is made too thick, carrier leakage from the well layer to the GaInAsP layer increases, and To deteriorates. Thus, when the GaInAsP layer is used as a barrier layer, the thickness of the GaInAsP layer cannot be increased, and it is effective to provide guide layers on both sides of the quantum well active layer separately from the GaInAsP layer. is there.

In the first embodiment, the composition of the n-type Al _0.4 Ga _0.6 As guide layer 3 and the p-type Al _0.4 Ga _0.6 As guide layer 6 sandwiching the quantum well active layer 16 is changed for comparison. The LD of Example 3 was manufactured, and the LD of Comparative Example 3 was compared with the semiconductor laser device of the first embodiment. In the first embodiment, the n-type Al _0.4 Ga _0.6 As guide layer 3 is changed to an n-type GaInP layer, and the p-type Al _0.4 Ga _0.6 As guide layer 6 is changed to p. The LD of Comparative Example 4 was changed to a type GaInP layer, and the LD of Comparative Example 4 was compared with the semiconductor laser device of the first embodiment.

  When the GaInP layer is used as the guide layer as in the comparative example 4, the efficiency is lowered, the resistance is increased, a large current and voltage are required to produce the same light output, the power consumption is increased, and The temperature of the LD increased and the reliability decreased.

  On the other hand, when the AlGaAs layer is used as the guide layer as in the first embodiment and the comparative example 3, the efficiency is increased, the element resistance is lowered, and high output and low power consumption are possible. This is because when GaInP is used, the efficiency decreases and the operating voltage increases because the valence band discontinuity with the active layer becomes large, which becomes a large barrier against holes, and the hole injection efficiency decreases. It is thought that it was because.

  Further, by using the AlGaAs layer as a guide layer, To is improved and stable operation is performed at a high temperature. Compared to the case where the GaInP layer is used as the guide layer, the use of the AlGaAs layer as the guide layer increases the difference in the conduction band between the AlGaAs layer and the active layer, and carriers overflow from the well layer to the barrier layer. This is thought to be due to staying in the quantum well without leaking into the guide layer.

  When the GaInP layer is used as a guide layer, the GaInP layer does not contain Al. Therefore, it seems that the reliability is improved at first glance, but it has been found that the reliability at high output is actually worse. This is because the threshold current increases, the efficiency decreases, a large voltage is required to produce the same light output, the device temperature rises, ΔEc is small, and To is bad. It is presumed that this is due to a vicious circle in which the threshold current further increases.

  When the AlGaAs layer is used as a guide layer, there was an effect of securing To with an Al composition of 0.3 or more. Increasing the Al composition of the AlGaAs layer facilitates oxygen bonding, but the AlGaAs layer used as the guide layer has a smaller light distribution than the active layer. Did not affect much.

  In the first embodiment, an n-type GaAs substrate is used as a substrate, but when a p-type GaAs substrate is used and an n-type and a p-type having the above-described configuration are interchanged to produce an LD, To deteriorates. . This is because an intermediate layer is formed between the well layer and the barrier layer located on the p side with respect to the well layer, so that electrons injected into the well layer easily leak into the level of the intermediate layer. It is thought that it was because of.

  On the other hand, when an n-type substrate is used, since an intermediate layer is formed between the well layer and the barrier layer located on the n side with respect to the well layer, electrons pass through the level of the intermediate layer. It is considered that To is hard to decrease because electrons injected into the well layer are less likely to leak into the barrier layer.

In the first embodiment, a GaAs intermediate layer is provided between the In _0.2 Ga _0.8 As _0.45 P _0.55 barrier layers 4A and 4B and the In _0.07 Ga _0.93 As well layers 5A and 5B. The layers 14A and 14B are arranged. However, even if the layers are other than the GaAs intermediate layers 14A and 14B, they may be arranged as long as the group III does not contain In and the group V is composed of one element. Good.

[Second Embodiment]
FIG. 3 is a schematic sectional view of a semiconductor laser device according to the second embodiment of the present invention. 3, the same components as those of the semiconductor laser device according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals as those of the components in FIG.

In FIG. 3, 4C is an undoped Ga _0.85 In _0.15 As _0.5 P _0.5 barrier layer having a thickness of 5 nm, and 4D is an undoped Ga _0.85 In _0.15 As _0.5 P having a thickness of 20 nm. _0.5 barrier layer, 15 is a p-type Ga _0.84 In _0.16 As _0.4 P _0.6 barrier forming layer having a thickness of 15 nm, 22 is a p-type GaAs cap layer having a thickness of 0.5 μm, 24A, 24B, 24C, 24D, 24E, and 24F are GaAs intermediate layers having a thickness of 1 nm, and 25A, 25B, and 25C are Ga _0.95 In _0.05 As well layers having a thickness of 4.2 nm.

Here, the undoped Ga _0.85 In _0.15 As _0.5 P _0.5 barrier layer 4D is an example of a III-V compound semiconductor barrier layer, GaAs intermediate layers 24A, 24B, 24C, 24D, 24E, 24F. Is an example of a III-V compound semiconductor intermediate layer, and Ga _0.95 In _0.05 As well layers 25A, 25B, and 25C are examples of well layers.

  Hereinafter, the manufacturing method of the semiconductor laser device of the second embodiment will be described with reference to FIGS. 4A to 4C.

First, as shown in FIG. 4A, an n-type Al _0.5 Ga _0.5 As clad layer 2 having a thickness of 1.8 μm and an n-type Al _0.4 layer having a thickness of 0.1 μm are formed on an n-type GaAs substrate 1. Ga _0.6 As guide layer 3, undoped Ga _0.85 In _0.15 As _0.5 P _0.5 barrier layer 4A with a thickness of 20 nm, GaAs intermediate layer 24A with a thickness of 1 nm, Ga with a thickness of 4.2 nm _0.95 In _0.05 As well layer 25A, 1 nm thick GaAs intermediate layer 24B, 5 nm thick undoped Ga _0.85 In _0.15 As _0.5 P _0.5 barrier layer 4B, 1 nm thick GaAs intermediate layer 24C, 4.2 nm thick Ga _0.95 In _0.05 As well layer 25B, 1 nm thick GaAs intermediate layer 24D, 5 nm thick undoped Ga _0.85 In _0.15 As _0.5 P _0.5 Bali Layer 4C, GaAs intermediate layer 24E having a thickness of 1nm, _Ga 0.95 _{In 0.05} As well layer 25C having a thickness of 4.2 nm, GaAs intermediate layer 24F with a thickness of 1 nm, a thickness of 20nm undoped _{Ga 0.85} an In _0.15 As _0.5 P _0.5 barrier layer 4D, p-type Al _0.4 Ga _0.6 As guide layer 6 having a thickness of 0.1 μm, p-type Al _0.5 Ga _{0 having} a thickness of 0.15 μm _.5 As first cladding layer 7, p-type Ga _0.84 In _0.16 As _0.4 P _0.6 barrier formation layer 15 with a thickness of 15 nm, p-type Al _0.5 Ga _{0 with} a thickness of 1.28 μm _.5 As second cladding layer 9 and p-type GaAs cap layer 22 having a thickness of 0.5 μm are sequentially formed by crystal growth by MOCVD.

When the crystal growth is performed, the p-type GaAs cap layer 22 is doped with an impurity density of 1 × 10 ²⁰ cm ⁻³ so that only the uppermost layer of 0.3 μm can easily contact the electrode.

  A layer extending from the barrier layer 4A to the opposite side of the n-type GaAs substrate 1 to the barrier layer 4D, that is, a layer between the n-type AlGaAs guide layer 3 and the p-type AlGaAs guide layer 6 is a TQW (Triple Quantum). A quantum well active layer 26 having a well (triple quantum well) structure is formed.

  The barrier layers 4A to 4D are not limited to the composition of the second embodiment.

Next, a resist mask (not shown) having a width of 6 μm is formed on the p-type GaAs cap layer 22 by a normal photolithography technique, and the p-type GaAs cap layer 22 and the p-type Al _0.5 other than the resist mask are formed. The Ga _0.5 As second cladding layer 9 is removed by etching, and as shown in FIG. 4B, a stripe shape comprising a p-type GaAs cap layer 22 and a p-type Al _0.5 Ga _0.5 As second cladding layer 9 is formed. Forming a ridge.

When the ridge is formed, the p-type Al _0.5 Ga _0.5 As second cladding layer 9 and the p-type Ga _0.84 In _0.16 As _0.4 P _0.6 layer 14 have high selectivity. Using an etchant, the etching is stopped at the p-type Ga _0.84 In _0.16 As _0.4 P _0.6 barrier formation layer 15 to control the ridge width. In the second embodiment, the etching is adjusted so that the width of the bottom of the ridge is 2.7 μm.

  Next, after removing the resist mask on the ridge, the wafer having the laminated structure of FIG. 4B is polished to a thickness of 100 μm, and a Ti / Pt / Au electrode 23 is deposited on the p side as shown in FIG. 4C. The AuGe / Ni / Au electrode 13B is formed on the n side by vapor deposition. That is, the Ti / Pt / Au electrode 23 is electrically connected to the p-type GaAs cap layer 22, and the AuGe / Ni / Au electrode 13B is electrically connected to the n-type GaAs substrate 1.

Next, the wafer having the structure of FIG. 4C is cleaved to form a plurality of laser bars having a width of 500 μm, and then a Si film and an Al ₂ O ₃ film are formed on one end face of each laser bar so that the reflectance is 5%. Is formed by vapor deposition, and an Si film and an Al ₂ O ₃ film are formed on the other end face of each laser bar by vapor deposition so that the reflectance is 90%. One end surface of the laser bar and the other end surface of the laser bar are formed to be perpendicular to the extending direction of the ridge.

  Finally, each laser bar is divided to obtain a semiconductor laser device in a chip state.

  The oscillation wavelength of the semiconductor laser device thus fabricated was 868 nm at 25 ° C.

  In the second embodiment, current confinement to the ridge is realized by using a Schottky junction of the p-side electrode 23 with respect to the p-type GaInAsP barrier formation layer 15.

  Therefore, in the semiconductor laser device of the second embodiment, the manufacturing process is simplified and the manufacturing cost can be greatly reduced as compared with the semiconductor laser device of the first embodiment.

  As a result, it has become possible to provide a light source for spatial light transmission capable of high-speed modulation with high output, low power consumption, and low cost.

  Also in the second embodiment, as in the first embodiment, by forming the GaAs intermediate layers 24A to 24F, it is possible to avoid the influence of the composition fluctuation at the interface of the GaInAsP barrier layers 4A, 4B, and 4C. The reproducibility of characteristics and the in-plane distribution were improved, and stable LD operation became possible.

  In the second embodiment, since the GaAs intermediate layers 24A to 24F are formed on the upper and lower sides (the n-type GaAs substrate 1 side and the side opposite to the n-type GaAs substrate 1 side) of the well layers 25A to 25C, the well layers The influence of the GaInAsP barrier layers 4A to 4D on both upper and lower sides can be avoided.

  If the ridge protrudes spatially as in the second embodiment, the bottom of the ridge is likely to be affected by strain, and the reliability of the device may be lowered due to the strain. In particular, in a material system in which an active region is strained, the element is easily affected by the strain.

  Therefore, in the second embodiment, the well layers 25A to 25C are made compressive strain and the barrier layers 4A to 4D are made tensile strain, so that the bottom portion of the ridge is hardly affected by the strain, and the reliability is prevented from being lowered.

  In the second embodiment, the well-free GaAs intermediate layers 24A to 24F are formed between the well layers 25A to 25C having compressive strain and the barrier layers 4A to 4D having tensile strain. The relative strain between the layers 25A to 25C and the barrier layers 4A to 4D was alleviated, and the bottom portion of the ridge was not easily affected by the strain, and good reliability was obtained.

[Third Embodiment]
In FIG. 9, the schematic block diagram of the spatial transmission system of 3rd Embodiment of this invention is shown. This spatial transmission system performs spatial optical transmission of 100 Mbps.

  The spatial transmission system includes a mobile terminal 301 and an information server 302. Each of the portable terminal 301 and the information server 302 is equipped with an LD module.

  The LD module includes the first semiconductor laser device or the semiconductor laser device according to the second embodiment, and a resin containing a diffusing agent by sealing the semiconductor laser device.

  According to the spatial system having the above configuration, since the LD module is mounted on each of the portable terminal 301 and the information server 302, a high-power and high-reliability semiconductor laser device serves as a light source. Therefore, a high-speed space of 100 Mbps Optical transmission was realized.

  In the third embodiment, bidirectional high-speed data transmission can be performed wirelessly between a portable terminal 301 such as an electronic notebook or a cellular phone and the information server 302. The LD module mounted on the portable terminal 301 is an LD module having a small diameter of 1.85 mm. The LD module mounted on the information server 302 is a 5 mm large-diameter LD module.

  The information server 302 stores moving image data, high-quality image data, high-quality music data, and the like. These data can be downloaded to the mobile terminal 101. Since these data have large capacities, when they are transmitted using conventional IrDA, it takes 10 seconds to several tens of seconds or more, so the usability is not necessarily good.

  On the other hand, in the third embodiment, data can be downloaded at high speed because data transmission can be performed at high speed by using the LD module having the semiconductor laser device of the first and second embodiments. This makes it possible to transmit data frequently and easily, and the convenience has improved dramatically.

  In particular, by using a large-diameter LD module for the information server 302, eye safety can be ensured even for high LD output as in the semiconductor laser devices of the first and second embodiments, and higher output can be achieved. In addition, a reliable and stable LD can be used, and high-speed spatial light transmission over a long transmission distance can be realized.

  The spatial light transmission system of the present invention is not limited to the illustrated example of the third embodiment.

  In the first to third embodiments, it goes without saying that various changes may be made without departing from the scope of the invention.

FIG. 1 is a schematic sectional view of a semiconductor laser device according to a first embodiment of the present invention. FIG. 2A is a schematic diagram for explaining a manufacturing process of the semiconductor laser device according to the first embodiment of the present invention. FIG. 2B is a schematic diagram for explaining a manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 2C is a schematic diagram for explaining a manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 2D is a schematic diagram for explaining a manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 2E is a schematic diagram for explaining the manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 2F is a schematic view for explaining the manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 3 is a schematic sectional view of a semiconductor laser device according to the second embodiment of the present invention. FIG. 4 is a schematic diagram for explaining a manufacturing process of the semiconductor laser device according to the second embodiment of the present invention. FIG. 4B is a schematic view for explaining a manufacturing process of the semiconductor laser device according to the second embodiment of the present invention. FIG. 4C is a schematic diagram for explaining a manufacturing process for the semiconductor laser device according to the second embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of a conventional semiconductor laser device. FIG. 6 is a graph showing the relationship between the thickness of the GaAs intermediate layer and the temperature characteristic To. FIG. 7 is a diagram showing the relationship between the thickness of the GaAs intermediate layer, the threshold current, and the efficiency. FIG. 8A is an energy band diagram of a quantum well structure without a GaAs intermediate layer. FIG. 8B is an energy band diagram of the quantum well structure when the GaAs intermediate layer is thin. FIG. 8C is an energy band diagram of the quantum well structure when the GaAs intermediate layer is thick. 8 is an energy band diagram of the quantum well structure when the DGaAs intermediate layer is on both sides. FIG. 9 is a schematic configuration diagram of a spatial light transmission system according to the third embodiment of the present invention.

1 n-type GaAs substrate 2 n-type Al _0.5 Ga _0.5 As cladding layer 3 n-type Al _0.4 Ga _0.6 As guide layers 4A, 4B, 4C, 4D Undoped In _0.2 Ga _0.8 As _0.45 P _0.55 barrier layer,
5A, 5B Undoped In _0.07 Ga _0.93 As well layer 6 p-type Al _0.4 Ga _0.6 As guide layer 7 p-type Al _0.5 Ga _0.5 As first cladding layer 8 p-type GaAs etching Stop layer 9 p-type Al _0.5 Ga _0.5 As second cladding layer 10 n-type Al _0.7 Ga _0.3 As block layer 11 n-type GaAs block layer 12 p-type GaAs cap layer 12a First crystal growth P-type GaAs cap layer 12b formed by the second crystal growth p-type GaAs cap layer 12c formed by the third crystal growth p-type GaAs cap layer 13A p-side AuZn / Au electrode 13B n-side AuGe / Ni / Au electrodes 14A, 14B undoped GaAs intermediate layer 15 p-type _Ga 0.84 _In 0.16 _As 0.4 _{P 0.6} barrier type Layer 16 quantum well active layer 24A, 24B, 24C, 24D, 24E, 24F GaAs intermediate layer _{25A, 25B, 25C Ga 0.95 In} 0.05 As well layer 26 quantum well active layer 301 portable terminal 302 the information server

Claims (8)

In a semiconductor laser device having an oscillation wavelength of 850 nm to 900 nm,
A first conductivity type GaAs substrate;
A lower cladding layer of a first conductivity type formed on the GaAs substrate;
A lower guide layer of a first conductivity type formed on the lower cladding layer;
An active layer formed on the lower guide layer and having a quantum well structure;
An upper guide layer of a second conductivity type formed on the active layer;
An upper cladding layer of a second conductivity type formed on the upper guide layer,
The active layer is
Well layers,
A III-V group compound semiconductor barrier layer sandwiching the well layer and containing at least In as a group III element and at least As and P as a group V element;
It is provided between the well layer and the barrier layer on the GaAs substrate side, does not contain In as a group III element, contains an element other than In, and contains only one element as a group V element III possess a -V compound semiconductor intermediate layer,
A semiconductor laser device, wherein the active layer does not contain Al . The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the III-V compound semiconductor intermediate layer is made of GaAs. The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the thickness of the III-V compound semiconductor intermediate layer is 0.5 nm or more and 2 nm or less. The semiconductor laser device according to claim 1,
The III-V compound semiconductor barrier layer is made of GaInAsP,
The well layer is made of GaInAs;
The ratio of In in the group III element of the III-V compound semiconductor barrier layer is larger than the ratio of In in the group III element of the well layer,
A semiconductor laser device, wherein a well width of the well layer is 6 nm or less. The semiconductor laser device according to claim 4 ,
A semiconductor laser device, wherein a well width of the well layer is 4 nm or more. The semiconductor laser device according to claim 4 ,
The semiconductor laser device, wherein the guide layer is made of Al _x Ga _1-x As (x ≧ 0.3). A semiconductor laser device manufacturing method for manufacturing the semiconductor laser device according to claim 1, comprising:
A method of manufacturing a semiconductor laser device, comprising: forming the III-V compound semiconductor intermediate layer by MOCVD after forming the III-V compound semiconductor barrier layer and before forming the well layer.   A spatial light transmission system comprising the semiconductor laser device according to claim 1.

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