JPS5836511B2 - Manufacturing method of semiconductor laser device with waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor laser device with a waveguide suitable for use in an optical integrated circuit.

When a semiconductor laser is used as a light emitting source in an optical integrated circuit, the optical waveguide coupled to the laser must be able to: (1) effectively guide the oscillated light, and (2) modulate the oscillated light passing through the waveguide. (3) It is required that the modulated light can be transmitted through the next element 1 without attenuation or divergence.

From the point of view of manufacturing optical integrated circuits, it is desirable to be able to manufacture laser elements and waveguides using the simplest possible method with good reproducibility! Of course it's a good thing.

The first semiconductor laser device with a waveguide manufactured using the conventional method
In Figure a, the second layer n-Ga. yA1y
Figure 2b shows the change in As2 thickness depending on the location, and Figure 1C shows the change in the concentration of A1 in the second layer depending on the location.

This device uses an epitaxial growth method to form an active region on a nGa1 XAIXA81 substrate.

A1a forms As2, but in this case D-G
The film thickness on the oscillation side (right side in the drawing) of a1-yAlyAs2 must be made thicker than that on the injection side (left side in the drawing).

This is because, if both sides are made to have a uniform film thickness, the laser light emitted from the oscillation side will diverge and become shattered due to light diffraction.

In addition, a partition plate (not shown) is provided on top of n鵠a,-yAlyA s2, and Evita? The laser element part and the waveguide part are made in one process using the crystal growth method.

However, devices manufactured by such conventional methods do not meet the above 1.
Although the above requirements are met, the film thickness near B of Ga1AyAs2 is extremely thicker than other parts, resulting in a drawback that the laser oscillation threshold becomes high and the oscillation mode becomes complicated. .

1. The cavity surface of the laser consists of two surfaces A and D, but there is no current injection on the right side of C, so there is no laser gain, and therefore the oscillation threshold increases from this point as well. Another drawback was that continuous oscillation was extremely difficult.

Moreover, it is difficult to form a layer with different thicknesses on the oscillation side and the injection side of n-Ga1-yAlyAs2.

The present invention provides a semiconductor laser device with a waveguide that satisfies the requirements of items 1 to 3 above and can eliminate the drawbacks of conventional devices.

Without further ado, a first embodiment of the present invention will be described with reference to the drawings.

A cross-sectional view of this device is shown in FIG. 2a, and a plan view is shown in FIG. 2b.

This device has an n-GaAs substrate and an n-Ga1
-XAIXAS1,n or PG81,7AI,As2
, P-Ga1xAlxAs3&Sequentially epitaxial growth is performed to create a semiconductor device, and within the device, P-Ga1xAlxAs3, except for the area that will become the laser oscillation element part,
Ga1-yA1yAs2, sometimes n-Ga1-xA
IXAs1 is also etched away, and Ga1 is deposited on at least two sides A and B that constitute the laser cavity among the four sides of the laser element portion formed after the etching removal.
, SiQ2 film with a lower refractive index than AI,j-, S
An insulating film 8 such as an i3 N4' film is attached, and a crystal layer 10 of GaAs,=P, etc. is formed by a vapor phase epitaxial method in the depressed region by etching removal, and its height is equal to the surface of the laser element part. Ohmic electrode 5 is placed on the laser element part and GaA is placed on the waveguide surface.
A metal 15 serving as an anti-Shite Schottky electrode is formed on q1 and Pz.

GaAs1-2Pz1 deposited by vapor phase epitaxial method
The refractive index distribution in the growth direction of 0 is shown in FIG. 3a.

The refractive index distribution can be obtained by changing the phosphorus concentration in the longitudinal direction, by changing the impurity concentration in the growth direction while keeping the phosphorus concentration constant, or by using a combination of the two.

Figure 3b shows the phosphorus concentration that was changed to obtain the refractive index distribution shown in Figure 3a. C shows the impurity concentration.

The features of the laser device of the embodiment of the present invention manufactured by the above method will be described below.

Unlike the conventional example shown in FIG. 1, the apparatus of the present invention manufactures the laser element part and the optical waveguide independently, so the thickness and impurity concentration of each part can be controlled very precisely.

The cavity surface of the twisted laser element is composed of A and B, and the current is uniformly injected over the entire area, so unlike the case in Figure 1, the laser gain exists uniformly, and therefore oscillation occurs. The threshold value is also lowered, making continuous oscillation easier.

Although the surface forming the cavity is formed by etching, it has been confirmed through experiments that there is almost no difference in the oscillation threshold compared to the case where the cavity is formed by cleaving.

This means that a mirror surface with good parallelism can be formed even by etching.

In the above device, the oscillated light enters the waveguide 10 through the fi insulating film 8 having a thickness of several thousand amps.

Since the laser element portion and the waveguide are in close contact with each other, the oscillated light enters the waveguide from the edge C with almost no loss.

Compared to the forbidden band width of Al and As2 in the residual active region, GaAs1-. Z. By increasing the forbidden band width of P40, the oscillated light propagates in the waveguide without suffering absorption loss.

Furthermore, the refractive index distribution of the pin k11Pz1o is such that the refractive index is maximum at the side surface of the active region 2 and decreases as it moves away from the side surface of the active region 2, as shown in FIG. 3a, so that the oscillated light It propagates through the waveguide without spreading due to diffraction.

In order to minimize the diffraction loss, the refractive index distribution shown in FIG. 3a should be made to lie on a square curve.

This is based on the same principle as the so-called self-focusing fiber, but vapor phase epitaxial growth is optimal for obtaining a refractive index distribution along a square curve.

That is, in the liquid phase epitaxial growth method, the refractive index can only be changed stepwise, but in the vapor phase epitaxial growth method, the molar ratio of phosphorus in GaAs 1 and P2 (i.e., 2) can be changed continuously. This is because the refractive index can also be changed in a curved manner.

Next, we will explain how to modulate the oscillated light using this device.

When a voltage is applied between the Schottky electrode 15 formed of GaAsl zpzlO and the electrode 4 in FIG. 2a, a depletion layer is formed directly under the Schottky electrode.

2 changes in the growth direction of GaAs1) pz,o are shown in Figure 3b.
of? The impurity concentration is uniformly 2×10
Consider the case of n-type with 1”cm 3 .

This value is an impurity concentration that can be easily obtained when grown without adding any impurities by the vapor phase epitaxial method.

The first layer is one piece.

．． 7A10. ．． The thickness is 3 μm as 3As1, the thickness is 0.3 μm as the second layer is nGaOg5Al005As2, and the third layer is P-Ga01.7.
Al+. Let us take as an example the case where the thickness of '3AS3 is 0.7 μm and the Schottky electrode is made of Au5 with a thickness of 0.5 μm.

In this case, FIG. 4 shows the results of an experiment in which a negative voltage was applied to the Au electrode 15 with respect to the electrode 4 to modulate the oscillation light.

The figure shows 0 for Au 15 for 20 ns width pulse oscillation light.
, -10, -20, and -30'V are applied for modulation, and the peak value and time response of the modulated output are compared.

The modulated output at voltages below -30V is almost the same as that at -30V.

From this figure, it is clearly seen that the oscillated light is intensity-modulated and phase-modulated by the reverse voltage applied to the electrode 5.

This is thought to be due to the fact that the optical permittivity of GaAs 1 and P2 changes due to the electric field, resulting in modulation.

At -30V, the tip of the depletion layer is active region 2 and n -Ga,
．． 7Al. Therefore, no matter how much voltage is applied below -30V, the modulated output will be -
It is thought that it will be the same as in the case of 30V.

As shown in this example, it is clearly seen that modulation can be easily applied to the waveguide in the device of the present invention with a low voltage.

The impurity concentration in the waveguide is set to 10 −1 3 to 1015z3
By setting the modulation voltage to 10-1 in the above example,
It is possible to reduce the impurity concentration to about ~10-3, but this impurity concentration can be obtained relatively easily with the vapor phase epitaxial method.For this reason, it is preferable to grow waveguides using the vapor phase epitaxial method. It can be seen that

Even when the refractive index distribution in the waveguide is changed by changing the impurity concentration distribution as shown in Figure 3C, the oscillation light can be modulated by the width of the depletion layer under the Schottky electrode, as in the previous example. I can do it.

GaAs with impurity concentration distribution as shown in Figure 3C
6. 7 P 6. ．． The modulation characteristics when No. 3 was epitaxially grown for a waveguide were almost the same as those shown in FIG.

The phosphorus composition ratio of Ga1-2 in the direction of the 1st direction is as shown in Figure 3b, and the impurity concentration distribution is as shown in Figure 3C. A field where light is modulated? , the voltage value required to obtain the modulation characteristics shown in FIG. 4 was approximately 2/3 of the voltage value shown in FIG.

From this, it can be seen that the modulation efficiency is improved by growing an epitaxial film for a waveguide in which both the phosphorus composition ratio and the impurity concentration are changed.

In the above example, a case was described in which GaAs 1 and P2 were used as the waveguide, but it goes without saying that similar results can be obtained by using Gal, AI, As'&.

Next, a second embodiment will be described with reference to the drawings.

Figure 5a shows a cross-sectional view of the device manufactured by the method of this example.
and b, and the plan view is shown in c, respectively.

The process of forming the insulating film 8 in the trench is the same as that in the first embodiment, and then etching is removed to form GaAs 1,P2(7)P in the bond area by vapor phase epitaxial method.
- Form an n-junction or a P-i-n junction so that its height is almost the same as the surface of the laser element, and place an ohmic electrode 5 on the laser element and GaAs on the waveguide surface.
11 Metal 1 that becomes an atomic electrode for P2 and 12
5 was formed.

Figure 5 a shows n-GaA81?213 and P-GaAs.
, P21 2 P1n junction is formed.

Figure 5b shows n→EaAs1-ZPZ 1 3 high resistance Ga
As1, P71 4, P of P-type GaAsi-z'z12
-1-n junction is formed.

GaAs 1, P2, deposited by gas phase epitaxial method
Figure 6a shows the change in the growth direction of 2, and Figure 6b shows the refractive index distribution.

FIG. 7 shows the change in impurity concentration in the growth direction in the case of FIG. 5a, and FIG. 8 shows the change in impurity concentration in the growth direction in the case of FIG. 5b.

As an example, Zn is doped as the P-type impurity and Te is doped as the N-type impurity.

Next, we will explain how to modulate the oscillated light using this device.

Referring to FIG. 5a, when a negative voltage is applied to electrode 7 with respect to electrode 4, n-GaA811P. 1.13 and P
A depletion layer is generated before and after the interface with the single part t1Pz 1 2.

1. If the impurity concentration distribution is as shown in Figure T,
The depletion layer mainly spreads toward the n-GaAs1, P213 side, and extends to the sides of the active region GalyAjyAs2.

GaAs 1, P7 in a region with a depletion layer. Since the optical dielectric constant of the depletion layer changes, the oscillation light changes and is modulated as the width of the depletion layer changes.

The impurity concentration distribution is as shown in Figure 7, and n-Ga1
-x' product 1 x = 0. 3, its thickness is 3μ
rn. y=o. of Ga1-yAlyAB2. As o5, its thickness is 0. 3μrrL. P-Gal, AI, As
3 x = 0. 3, its thickness is 1.7 μm.
N15M17z9 thickness is 4 μm, P-GaAs
,, Let us take as an example the case where the thickness of P210 is 1 μm.

The results of an experiment in which the oscillation light was modulated in that case were similar to those shown in FIG.

It is clearly seen that amplitude modulation and phase modulation can be easily applied to the waveguide in the device of this embodiment with low voltage.

The impurity concentration of n-GaAs 1, P21 3 was set to 10
, ' 1 3, ~ 1014z 3, the modulation voltage can be reduced to about 10-1 to 10-2 in the above example, but in the gas phase epitaxial method, this impurity concentration is also relatively low. It can be easily obtained, and from this fact it can be seen that the waveguide is excellently grown by the vapor phase epitaxial method.

Modulation can also be achieved by forming a P-i-n structure as shown in FIG. 5B and applying a negative voltage to the electrode 15 with respect to the electrode 4.

In this case, most of the applied voltage is applied to the i-layer 14, and by changing the applied voltage, the electric field in the i-layer 14 is changed, and the refractive index is changed by the electro-optic effect, thereby modulating the oscillated light. be.

The relationship between the applied voltage and the modulated output in this case is almost the same as that shown in FIG.

The reason why the active region 2 is made of Ga1, . . . AI- instead of GaAs is because the laser life is longer when the active region 2 is made of Ga1 and AlyAS than when it is made of GaAs.

In the above example, a case was described in which a waveguide made of GaAs1-ZPZ was used, but it goes without saying that similar results can be obtained using Ga1, Ai2, and As.

Next, a third embodiment will be described with reference to the drawings.

A sectional view of this device is shown in FIG. 9a, and a plan view is shown in FIG. 9b.

The old process of forming the GaAs 1, P2 layer 10 by the vapor phase epitaxial method in the area depressed by etching removal is the same as in the first embodiment, and then the SiO2 layer is formed on it.
An insulating film 16 and a metal electrode 15, such as two films, are formed.

GaAst-zPz deposited by vapor phase epitaxial method
Figure 10a shows the refractive index distribution in the growth direction of 10. Figure 10b shows the phosphorus concentration profile when changing the phosphorus concentration in the longitudinal direction as a method of obtaining the refractive index distribution, assuming the phosphorus concentration is constant. Figure C shows a profile when the impurity concentration in the growth direction is changed.

Next, we will explain how to modulate the oscillated light using this device.

What if GaAs,,P210 in Fig. 9a is P type? Considering this, when a positive voltage is applied to the electrode 15 with respect to the electrode 4, a depletion layer is generated directly under the insulating film 8, and as the applied voltage increases, the width of the depletion layer increases, and a depletion layer is formed on the side surface of the active region 2. It's growing.

Since the optical permittivity of GaAs 1 and P2 changes in the region where the depletion layer exists, the oscillation light changes and is modulated as the width of the depletion layer changes.

The change in Z in the growth direction of GaAsl,P2,10 is the first
The impurity concentration is uniformly 5 as shown in Figure 0b.
Assume that it is a P type with a diameter of X10”°ffi3.

The first layer of the laser element is n-ro7 AI. ). 3As
1 with a thickness of 3 μm, the second layer is n-”0.9 5AI
.

．． , o5AI32, 0.4 pm thick, third layer is P-Ga
．． 2A1o3As 3 with 0.5 p. Thickness in m, P-G
It is assumed that aAs 1-zPz 10 has a thickness of 3.9 μm and its height coincides with the laser element portion.

As an insulating film 8' on the surface of the GaAst-zPz layer, 500m of Si is deposited, and an Au electrode 15 is deposited thereon to a thickness of 1 μm.

In this case, FIG. 11 shows the experimental results in which a positive voltage was applied to the Au electrode 15 to modulate the oscillation light.

The figure shows 0, 0.5, 1.0, 1.5V applied to the Au electrode 15 for pulsed light with a width of 20ns.
This is a comparison of the peak value and time response of the modulated output when modulated by applying a DC voltage of .

The modulated output for voltages below 1.5V is almost the same as that for 1.5V.

This is thought to be because a strong inversion layer is formed on the surface of GaAs1, P210 at 1.5μ, so that the depletion layer does not expand even if a voltage is applied any further.

As shown in this example, it is clearly seen that amplitude modulation and phase modulation can be easily applied to the waveguide in the device of the present invention with low voltage.

Ga with different impurity concentration distribution as shown in Figure 10C
As.

, 7PO, 3 as a waveguide, the modulation characteristics were almost the same as those shown in FIG.

When a waveguide is formed in which both the phosphorus concentration distribution and the impurity concentration of GaAs 1 and P2 in the growth direction are changed as shown in FIGS. 10b and 10C, and a modulation voltage is applied to modulate the oscillation light, The voltage value was approximately V3 shown in FIG.

From this, it can be seen that the modulation efficiency is improved by creating a waveguide in which both the phosphorus molar ratio and the impurity concentration are changed.

Although the above example describes the case where GaAs11Pz is used as the waveguide, it goes without saying that similar results can be obtained using GaI JlzAs.

[Brief explanation of drawings]

Figure 1a is a cross-sectional view of a laser device with a waveguide in the conventional method, b is a relationship between the location and thickness of the active region layer of the same laser device, and C is a relationship between the location and the likely concentration in the active region. Relationship diagrams, FIG. 2a is a sectional view of a laser device with a waveguide in the method of the first embodiment of the present invention, b is a plan view, and FIG. 3a is a Ga
The refractive index distribution diagram in the predetermined direction of As 1, P2, b is the refractive index distribution diagram when the phosphorus concentration is changed, C is the refractive index distribution diagram when the impurity concentration is changed, and Figure 4 is the same laser. Characteristic diagrams of experimental results in which a modulation voltage was applied to the device to modulate the oscillated light, FIGS. Figure 6 a is GaA
A diagram showing the change in Z in the growth direction of s1, P2, b is its refractive index distribution diagram, Figure 7 is an impurity concentration distribution diagram in the waveguide of the same laser device, and Figure 8 is the impurity concentration distribution diagram in the waveguide of the same laser device. 9a is a sectional view of a laser device with a waveguide for the method of the third embodiment of the present invention, FIG. 9b is a plan view of the same, and FIG. 10a is a diagram showing changes in optical output with respect to reverse voltage. A refractive index distribution diagram in the waveguide of the laser device, b is a refractive index distribution diagram when changing the phosphorus concentration, C is a refractive index distribution diagram when changing the impurity concentration,
FIG. 11 is a characteristic diagram of experimental results in which a modulation voltage was applied to the same laser device to modulate the oscillation light. 1...n-Ga1, cAl book 2...
n or P 1 piece, 3...P package, 1-,
4...5...Automikku electrode, 8...
...Insulating film, 10...Crystal layer, 1 2 =
=・P-GaAs1, P, 1 3==・n-Gak3
,,P2,15... Electrode.

Claims (1)

[Scope of Claims] 1. A step of forming each layer including an active layer for forming a laser element on a semiconductor substrate, and forming each layer other than a region that will become the laser element at least until the active layer is removed. a step of removing the active layer from the surface; a step of forming an insulating film having a refractive index lower than that of the active layer on at least two side surfaces constituting a cavity surface among the four side surfaces of the laser element formed after the removal; A step of forming a waveguide crystal layer made of GaAs1zz and having a curved refractive index distribution using the vapor phase epitaxial P method on the obtained portion, and providing a control electrode for laser light modulation on the surface of the crystal layer. 1. A method for manufacturing a semiconductor laser device with a waveguide, comprising the steps of: 2. The method of manufacturing a semiconductor laser device with a waveguide according to claim 1, wherein the control electrode is a Schottky electrode. 3 The crystal layer is a p-n junction 1 or a p-i-
2. The method of manufacturing a semiconductor laser device with a waveguide according to claim 1, wherein the semiconductor laser device has an n-junction structure and the control electrode is an ohmic electrode. 4. The method of manufacturing a waveguide semiconductor laser device according to claim 1, wherein the control electrode is an electrode that is insulated and separated from the crystal layer.