JP4076733B2 - Surface type optical-optical switch and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical semiconductor device that performs an optical logic / optical switch operation that can be used for an optical switch / optical repeater and the like that are expected to constitute an optical communication / optical information processing system. More specifically, the present invention relates to a planar optical-optical switch that utilizes optical nonlinearity of a semiconductor multiple quantum well (MQW) structure thin film.
[0002]
[Prior art]
Conventionally, prior art documents in such fields include the following.
[1] JP-A-7-325275 [2] JP-A-7-36065 [3] R.A. Jin, et, al. , Appl. Phys. Lett. , 61 (15), 12 Oct. p. 1745 (1992)
[4] M.M. H. Moloney, et. al. , Appl. Phys. Lett. , 64 (8), 21 Feb. p. 997 (1994)
The structure of the conventional optical-optical switch using the optical nonlinearity of the MQW structure thin film (the effect that a large amount of carriers are generated by irradiating strong light, resulting in a decrease in absorption coefficient and a change in refractive index) is a refractive index. There are a dispersion type that uses change and an absorption type that uses the effect of reducing the absorption coefficient (bleaching). In either case, the MQW structure thin film is sandwiched between two reflective films.
[0003]
FIG. 8 is a diagram showing the optical nonlinearity of the light absorption spectrum and the refractive index spectrum of the MQW structure thin film. FIG. 8A shows the wavelength (nm) on the horizontal axis and the absorption coefficient (× 10 ⁴ cm ^{−1 on the} vertical axis. FIG. 8B shows the wavelength (nm) on the horizontal axis and the refractive index change Δn on the vertical axis.
[0004]
In the case of a dispersion type optical-optical switch, in order to increase the extinction ratio, it is necessary to increase the reflectivity of the reflection film and increase the Q value. This makes it difficult to manufacture the device. Therefore, the absorption type shown in FIG. 9A has relaxed the restriction on the signal wavelength.
[0005]
The absorption type is set to the wavelength of the exciton absorption peak existing at a slightly lower energy of the ground quantum level of the MQW structure thin film for both the signal light Ps and the control light Pc. At this time, both surfaces of the element are provided with antireflection films, and as shown in the graph of FIG. 9B, when the control light Pc is irradiated, the carriers are excited, and the signal light Ps is bleached. And signal light Ps is transmitted.
[0006]
Furthermore, by adopting a reflection type as shown in FIG. 9C, the optical nonlinear characteristic can be enhanced and the extinction ratio can be increased. In particular, in the absorption type, the bleaching characteristic does not change steeply with respect to the intensity of the control light Pc. Therefore, regarding the low reflection film and the high reflection film arranged so as to sandwich the MQW structure thin film, the distance between the low reflection film and the high reflection film is set to the optical length (m + 1/2) λ / 2 (where m is The reflectance of the low reflection film is set to be substantially equal to the reflectance of the MQW structure thin film having the high reflection film when the control light Pc is not irradiated with respect to the signal light Ps. A structure in which the signal light Ps is incident from the low reflection film side, reflected by the high reflection film, and emitted from the low reflection film side has been adopted, and a large extinction ratio has been realized by the interference effect.
[0007]
[Problems to be solved by the invention]
However, in the conventional optical-optical switch using the optical nonlinearity of the MQW structure thin film described above, the time until the value of the absorption coefficient is restored to the original large value after the strong control light Pc disappears (absorption recovery time). : Τ) takes about 1 picosecond, and it was difficult to further reduce this.
[0008]
Further, in order to realize a response of about 1 picosecond, the MQW structure thin film needs to be grown at a temperature much lower than the normal growth temperature used in the molecular beam epitaxy (MBE) method (see above). Therefore, a large amount of crystal defects such as lattice defects are included in the manufactured crystal. For this reason, there has been a problem that the properties of the crystals themselves lack long-term stability.
[0009]
Further, a process of adding a large amount of p-type dopant such as Be and performing a heat treatment for several minutes at a temperature of about 600 ° C. after the growth is necessary (see the above-mentioned prior art document [2]). In this way, the manufacturing process is complicated, and manufacturing conditions such as low-temperature growth and heat treatment that are unusual or difficult to establish must be used, so there are problems in terms of yield and reproducibility. Is leaving.
[0010]
In view of the above circumstances, an object of the present invention is to provide a surface-type optical-optical switch that can improve absorption recovery time and realize extremely fast responsiveness, and a method for manufacturing the same.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] A semiconductor multiple quantum well structure thin film, and a low reflection film and a high reflection film disposed so as to sandwich the semiconductor multiple quantum well structure thin film, and signal light is incident from the low reflection film side, In a surface light-optical switch that is configured to be reflected by a high reflection film and output from the low reflection film side, and to control on / off of the signal light by turning on / off of the control light, the control light and the signal light wavelength, the semiconductor multi-quantum well structure ground quantum level of the thin film (n = 1), rather than the high-order quantum level (n ≧ 2) by that matches the corresponding wavelength urchin semiconductor multiple quantum well structure It is characterized by comprising.
[0012]
[2] having a semiconductor multiple quantum well structure thin film, a low reflection film and a high reflection film disposed so as to sandwich the semiconductor multiple quantum well structure thin film, signal light is incident from the low reflection film side, In the manufacturing method of the surface light-optical switch, which is configured to reflect the high reflection film and emit from the low reflection film side, and to control the on / off of the signal light by the on / off of the control light, the control light and the wavelength of the signal light, the semiconductor multi-quantum well structure ground quantum level of the thin film (n = 1), rather than higher-order quantum level (n ≧ 2) by that matches the corresponding wavelength urchin semiconductor multiple quantum The method includes a step of forming a well structure and a step of growing the semiconductor multiple quantum well structure thin film by a molecular beam epitaxy method.
[0013]
[3] In the method for manufacturing a planar optical-optical switch according to [2], the semiconductor multiple quantum well structure thin film contains one or more Be or other p-type dopants at 1 × 10 ¹⁷ cm ^−3. It is characterized by being added at the above concentration.
[0014]
[4] In the method for manufacturing a planar optical-optical switch according to [2] above, the semiconductor multiple quantum well structure thin film contains one or more Si or other n-type dopants at 1 × 10 ¹⁷ cm ^−3. It is characterized by being added at the above concentration.
[0015]
[5] In the method for manufacturing a planar optical-optical switch according to [2], the semiconductor multiple quantum well structure thin film contains one or more Be or other p-type dopants at 1 × 10 ¹⁷ cm ^−3. One or more Si or another n-type dopant is added at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more at the above concentration.
[0016]
[6] In the method of manufacturing a planar optical-optical switch according to [2], a compressibility or stretchability of 0.5% or more is provided between the quantum well layer and the barrier layer of the semiconductor multiple quantum well structure thin film. The lattice distortion is included.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
FIG. 1 is a block diagram of a surface type optical-optical switch (MQW structure thin film) according to a first embodiment of the present invention.
[0019]
An embodiment of the present invention will be described for an MQW structure thin film made of GaAs and AlAs, which is the most basic material of a compound semiconductor.
[0020]
As shown in FIG. 1, the MQW structure thin film has an Al _0.3 Ga _0.7 As etch stop layer 11 and a (GaAs-AlAs) MQW at a growth temperature of 560 ° C. which is a growth temperature usually used on the GaAs substrate 10 by using the MBE method. A (100 period) layer 12 and an Al _0.3 Ga _0.7 As cap layer 13 were grown sequentially. A dopant is not intentionally added to the (GaAs-AlAs) MQW layer 12.
[0021]
FIG. 2 is a diagram showing an absorption spectrum with respect to the wavelength of the surface light-optical switch (MQW structure thin film).
[0022]
Here, the thickness of the (GaAs-AlAs) MQW quantum well layer 12 is 15 nm. After the growth, the GaAs substrate 10 is removed up to the Al _0.3 Ga _0.7 As etch stop layer 11 by chemical etching, and the absorption spectrum measured with weak light is shown in FIG.
[0023]
Since the thickness of the (GaAs-AlAs) MQW quantum well layer 12 of this sample is set to be slightly thicker than usual, the absorption peak of excitons of heavy holes (hh) appearing at the absorption edge and light holes ( lh) exciton peaks overlap so that they look like a single peak. The peak at n = 1 appears at the wavelength λ = 855 nm, and the peak at n = 2 appears at the wavelength λ = 819 nm.
[0024]
FIG. 3 is a diagram showing a time response waveform as a result of measuring the absorption recovery time τ using a pump-probe method using laser light pulses of these wavelengths.
[0025]
As shown in this figure, as a result of measuring the absorption recovery time τ using the pump-probe method using the laser light pulse with the wavelength λ = 855 nm and the wavelength λ = 819 nm, τ = 80 pico at the wavelength λ = 855 nm. It has been experimentally shown that there is a one-digit difference from τ = 8 picoseconds at a second, wavelength λ = 819 nm.
[0026]
Note that FIG. 2 shows a saturation excitation light density Is measured using laser light of various wavelengths (a measure of the magnitude of optical nonlinearity indicating that optical bleaching occurs even with weak light as this value is smaller. 7, which will be described later in detail), Is is about an order of magnitude larger near the wavelength of n = 2 than the wavelength of n = 1. This indicates that optical bleaching is unlikely to occur in the vicinity of n = 2, but also includes an apparent effect that Is is measured to be large because the absorption coefficient itself is large.
[0027]
Hereinafter, other embodiments of the present invention will be described.
[0028]
FIG. 4 is a block diagram of a surface type optical-optical switch (MQW structure thin film) showing a second embodiment of the present invention.
[0029]
In this embodiment, an Al _0.3 Ga _0.7 As etch stop layer 11 and a Be- (GaAs-AlAs) MQW (100 cycles) at a growth temperature of 600 ° C., which is a growth temperature usually used on the GaAs substrate 10 by using the MBE method. A layer 12 ′ and an Al _0.3 Ga _0.7 As cap layer 13 were sequentially grown. The Be- (GaAs-AlAs) MQW layer 12 'are uniformly doped at a concentration of Be as a dopant 7.8 × 10 ¹⁷ cm ^-3.
[0030]
Further, the thickness of the GaAs quantum well layer 12 'of Be- (GaAs-AlAs) MQW is set to 7 nm, which is close to a commonly used value. FIG. 5 shows an absorption spectrum measured with weak light after the growth, after removing the GaAs substrate 10 up to the Al _0.3 Ga _0.7 As etch stop layer 11 by chemical etching.
[0031]
Since this sample is doped with Be, the absorption peak of the exciton of heavy hole (hh) and the exciton peak of light hole (lh) appearing at the absorption edge overlap, and as a result, a single peak Looks like. The peak at n = 1 appears at the wavelength λ = 821 nm, and the peak at n = 2 appears at the wavelength λ = 741 nm.
[0032]
FIG. 6 shows time response waveforms as a result of measuring the absorption recovery time τ using the pump-probe method using laser light pulses of several wavelengths including these wavelengths, and the wavelengths λ = 821 nm and λ = 800 nm. In this experiment, τ = 60 picoseconds, and for wavelengths λ = 760 nm and λ = 741 nm, τ = 0.3 picoseconds or less (the time resolution of the measuring device is 0.2 picoseconds), which is a difference of two orders of magnitude or more. It is shown.
[0033]
In FIG. 5, the relationship between the absorption recovery time τ and the measurement wavelength λ is shown superimposed on the light absorption spectrum. It shows that τ changes sharply when the wavelength λ is between 780 nm and 800 nm.
[0034]
FIG. 7 shows how the light absorption coefficient (actually, the product αL of the light absorption coefficient and the total thickness of the quantum well layer) changes depending on the intensity of incident light, wavelength λ = 820 nm (n = 1 exciton absorption peak wavelength). ) And wavelength λ = 741 nm (n = 2 exciton absorption peak wavelength). α decreases with increasing incident light intensity.
α = α ₀ / (1 + I / Is) + β
Can be described as Is at this time is called a saturated excitation light density. A smaller value indicates that optical bleaching occurs even with weak light, and is a measure of the magnitude of optical nonlinearity.
[0035]
7 For λ = 820nm, Is = 50μJ / cm 2, the case of lambda = 741 nm, indicating that it is Is = 280μJ / cm ^2.
[0036]
FIG. 5 shows Is measured at various wavelengths λ superimposed on the light absorption spectrum. Again, Is is about an order of magnitude greater near the wavelength of n = 2 than the wavelength of n = 1. This indicates that optical bleaching is unlikely to occur in the vicinity of n = 2, but also includes an apparent effect that Is is measured to be large because the absorption coefficient itself is large.
[0037]
As described above, according to the present invention, the wavelength band corresponding to the higher-order quantum level (n ≧ 2) and the wavelengths of the control light and the signal light are not the ground quantum level (n = 1) of the MQW structure thin film. Although the case where the MQW structure is manufactured using the normal growth conditions in the MBE method has been described as the manufacturing condition of the MQW structure, the metal organic vapor phase deposition method ( It goes without saying that the same effect can be obtained even if it is fabricated using MOCVD) or other methods.
[0038]
Furthermore, although a sample doped with Be at a concentration of 7.8 × 10 ¹⁷ cm ⁻³ has been described as an MQW structure thin film, the concentration is not limited to this, and the concentration is 1 × 10 ¹⁷ cm ⁻³ or more. Good. Moreover, although Be was described as a dopant, it is not limited to this, The same effect is acquired even if it adds another p-type dopant, Si, or another n-type dopant. Furthermore, the same effect can be obtained by adding a plurality of types of dopants instead of a single type of dopant.
[0039]
As described above, optical bleaching is less likely to occur in the wavelength band near the quantum level of n = 2 than in the vicinity of the base quantum level. This means that control light having a higher intensity is required to perform the optical switching operation. In order to avoid this problem, a method using a strained quantum well structure is effective. In the vicinity of the wavelength band of the quantum level of n = 1, it is known that the strained quantum well structure has a smaller Is than the strainless quantum well structure (the prior art documents [3] and [4] described above). reference). Even in the present invention characterized in that a wavelength band corresponding to a higher-order quantum level is used, it is easily thought that Is can be reduced by adopting a strained quantum well structure.
[0040]
In the above description, a combination of GaAs and AlAs, which are typical compound semiconductor materials, has been described as the MQW structure thin film. However, the present invention is not limited to this, and other semiconductor combinations are natural. It is apparent that the present invention can also be applied to an MQW structure thin film using a material other than a compound semiconductor.
[0041]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0042]
【The invention's effect】
As described above in detail, in the present invention, the wavelengths of the control light and the signal light correspond to higher order quantum levels (n ≧ 2) instead of the ground quantum levels (n = 1) of the MQW structure thin film. by setting such a wavelength, a surface-type light has a very fast response speed - it is possible to realize an optical switch.
[0043]
That is, excitons that are resonantly excited to exciton absorption peaks associated with higher-order quantum levels by the control light are dissociated within a time of 100 to 200 femtoseconds as a result of collision with lattice vibration, and electron − It becomes hole plasma, and both electrons and holes relax to their respective ground quantum levels within the same amount of time.
[0044]
As a result, the absorption coefficient for the weak signal light is restored to the value of the large absorption coefficient before the control light arrives within τ = several hundred femtoseconds after the control light is cut off. In this way, for the MQW structure thin film, a planar light-light whose wavelength relationship is configured so that the exciton absorption peak wavelength associated with the higher-order quantum level coincides with or is close to the wavelength of the signal light or control light. The switch has a short response speed of less than τ = 1 picosecond.
[0045]
And since the MQW structure thin film used for this invention can be grown on normal conditions by MBE method etc., there is no instability of a material characteristic, it is excellent in reproducibility, and a manufacturing yield is very high.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a planar optical-optical switch (MQW structure thin film) according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an absorption spectrum with respect to wavelength of a surface-type optical-optical switch (MQW structure thin film) according to a first embodiment of the present invention.
FIG. 3 shows a result of measuring an absorption recovery time τ using a pump-probe method using a laser light pulse of a predetermined wavelength of a surface optical switch (MQW structure thin film) showing a first embodiment of the present invention. It is a figure which shows the time response waveform.
FIG. 4 is a configuration diagram of a planar optical-optical switch (MQW structure thin film) showing a second embodiment of the present invention.
FIG. 5 is a characteristic diagram with respect to wavelength of a surface-type optical-optical switch (MQW structure thin film) showing a second embodiment of the present invention.
FIG. 6 is a diagram showing a time response waveform of signal light of a surface-type optical-optical switch (MQW structure thin film) according to a second embodiment of the present invention.
FIG. 7 is a characteristic diagram of a light absorption coefficient with respect to incident light intensity of a surface light-optical switch (MQW structure thin film) showing a second embodiment of the present invention.
FIG. 8 is a diagram showing optical nonlinearity of a light absorption spectrum and a refractive index spectrum of a conventional MQW structure thin film.
FIG. 9 is an explanatory view of a conventional absorption type MQW structure thin film element.
[Explanation of symbols]
10 GaAs substrate 11 Al _0.3 Ga _0.7 As etch stop layer 12 (GaAs-AlAs) MQW (100 period) layer 12 'Be- (GaAs-AlAs) MQW (100 period) layer 13 Al _0.3 Ga _0.7 As cap layer

Claims (6)

A semiconductor multiple quantum well structure thin film, and a low reflection film and a high reflection film disposed so as to sandwich the semiconductor multiple quantum well structure thin film, and signal light is incident from the low reflection film side, and the high reflection film In a surface-type optical-optical switch that takes a configuration of being reflected from the low reflection film side and is emitted from the low reflection film side, and controlling on / off of the signal light by turning on / off of the control light, the wavelengths of the control light and the signal light are , configuring the semiconductor multiple quantum well structure ground quantum level of the thin film (n = 1), rather than higher-order quantum level (n ≧ 2) by that matches the corresponding wavelength urchin semiconductor multiple quantum well structure A surface-type optical-optical switch. A semiconductor multiple quantum well structure thin film, and a low reflection film and a high reflection film disposed so as to sandwich the semiconductor multiple quantum well structure thin film, and signal light is incident from the low reflection film side, and the high reflection film In the method of manufacturing the surface light-optical switch, which is configured to reflect the light from the low reflection film and emit light from the low reflection film side, and to control the on / off of the signal light by the on / off of the control light, the control light and the signal light wavelength, the semiconductor multi-quantum well structure ground quantum level of the thin film (n = 1), rather than the high-order quantum level (n ≧ 2) by that matches the corresponding wavelength urchin semiconductor multiple quantum well structure A method of manufacturing a planar optical-optical switch, comprising: a step of forming; and a step of growing the semiconductor multiple quantum well structure thin film by a molecular beam epitaxy method. 3. The planar light according to claim 2, wherein one or more Be or other p-type dopants are added to the semiconductor multiple quantum well structure thin film at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more. -Manufacturing method of optical switch. 3. The planar light according to claim 2, wherein one or more Si or other n-type dopants are added to the semiconductor multiple quantum well structure thin film at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more. -Manufacturing method of optical switch. The semiconductor multiple quantum well structure thin film has one or more Be or other p-type dopants at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more, and one or more Si or other n-type dopants. 3. The method of manufacturing a planar optical-optical switch according to claim 2, wherein the surface optical-optical switch is added at a concentration of 1 * 10 < ¹⁷ > cm < ^-3 > or more.   3. The planar light-light according to claim 2, wherein a compressive or extensible lattice strain of 0.5% or more is included between the quantum well layer and the barrier layer of the semiconductor multiple quantum well structure thin film. A method for manufacturing a switch.

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