JP2003332674A - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element whose end face is improved in thermal conductivity so as to enhance its output and reliability. <P>SOLUTION: An n-Ga<SB>1-z1</SB>Al<SB>z1</SB>As lower clad layer 12, an i-In<SB>0.49</SB>Ga<SB>0.51</SB>P lower optical waveguide layer 13, an In<SB>x3</SB>Ga<SB>1-x3</SB>As<SB>1-y3</SB>P<SB>y3</SB>quantum well active layer 14, an i-In<SB>0.49</SB>Ga<SB>0.51</SB>P upper optical waveguide layer 15, a p-Ga<SB>1-z1</SB>Al<SB>z1</SB>As upper first clad layer 16, a p-In<SB>0.49</SB>Ga<SB>0.51</SB>P etching stop layer 17, a p-Ga<SB>1-z1</SB>Al<SB>z1</SB>As upper second clad layer 18, a p-GaAs contact layer 19, an insulating film 20, a p-side electrode 21, and an n-side electrode 22 are successively formed on an n-GaAs substrate 11. An Al<SB>2</SB>O<SB>3</SB>low-reflection film 14 of thickness λ/4 is formed on one end face of a resonator, and a high-reflection film 13 of an oxide laminate (Al<SB>2</SB>O<SB>3</SB>/SiO<SB>2</SB>/Al<SB>2</SB>O<SB>3</SB>/SiO<SB>2</SB>/Al<SB>2</SB>O<SB>3</SB>/SiO<SB>2</SB>/Al<SB>2</SB>O<SB>3</SB>/SiO<SB>2</SB>/Al<SB>2</SB>O<SB>3</SB>/SiO<SB>2</SB>) having a reflectance of 95% or above, and a thickness of λ/4 is formed on the other end face of the resonator. The surface roughness of the first Al<SB>2</SB>O<SB>3</SB>layer of the oxide laminate as the reflection film is set at 3 nm or below. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device having no active layer containing Al.

[0002]

2. Description of the Related Art As a main factor that determines the life of a semiconductor laser device, optical damage destruction (COD) of an optical resonator
Optical Damage). This occurs because the cavity end face becomes an absorption region for the light generated inside the cavity. Specifically, dangling bonds are formed on the semiconductor surface of the cavity end face due to surface oxidation due to adsorption of oxygen and transformation of the semiconductor surface composition, which causes a deep level peculiar to the semiconductor interface and causes a forbidden band near the end face. This is because the width has become substantially narrower. Therefore, a method of eliminating the interface state is proposed in JP-A-9-162496 and JP-A-3-101183. Particularly in the latter, it is described that by attaching Si or the like to the end face of the semiconductor laser and eliminating the interface state at the end of the dangling bond, heat generation of the end face excited by the non-radiative recombination current can be suppressed. There is.

[0003]

On the other hand, in a semiconductor laser device having an oscillation wavelength in the range of 760 to 900 (nm), an Al-based active layer such as GaAlAs is used. In the intended semiconductor laser device, an active layer containing no aluminum, for example, InGaAsP is used. A semiconductor laser device having an active layer not containing aluminum generally has higher thermal resistance and poor heat dissipation than a semiconductor laser device having an Al-based active layer, or the non-radiative recombination rate due to an interface defect is Al. About 1 / th of that of the system
Due to such a small value as 10, there is a problem that a remarkable COD improvement result cannot be obtained even if the above method for reducing the interface state is applied.

In view of the above circumstances, the present invention is directed to a COD of optical output.
It is an object of the present invention to improve the level and provide a semiconductor laser device having high reliability.

[0005]

A semiconductor laser device according to the present invention comprises a semiconductor laminate including a light emitting layer and a waveguide layer, and a semiconductor provided with a passivation film made of an oxide on a cavity end face of the laminate. In the laser element, the surface roughness of the first layer from the layered body side of the passivation film is 3 nm or less.

The first layer from the side of the laminated body means the layer when the passivation film is a single layer, and the layer formed directly on the laminated body when the passivation film has a plurality of layers.

At least the first layer of the passivation film is preferably made of at least one oxide of Al, Si, Ti and Ta.

The light emitting layer and the waveguiding layer are preferably made of a semiconductor containing no Al.

At least the first layer of the passivation film is preferably formed by an electron cyclotron resonance plasma deposition method.

The above-mentioned "surface roughness" means the Pea in a 100 μm square area measured by an atomic force microscope.
Indicates the k-Valley maximum value (maximum height from the bottom of the concave to the top of the convex)

[0011]

According to the semiconductor laser device of the present invention, a semiconductor laser device is formed of a semiconductor laminate including a light emitting layer and a waveguide layer, and a passivation film made of an oxide is provided on a cavity end face of the laminate. In the above, by setting the surface roughness of the first layer to 3 nm or less from the laminated body side of the passivation film, the thermal conductivity of the film can be increased and the temperature rise of the cavity facets can be suppressed. This allows
Since it is possible to increase the light output level that reaches the end face destruction, it is possible to improve the light output and reliability.

In particular, the first direct formation on the semiconductor laminate
Since the layer greatly contributes to the improvement of heat dissipation, the surface roughness is 3
The thickness of not more than nm is effective for improving the light output and reliability.

Particularly, in a semiconductor laser device having an active layer containing no Al, the heat dissipation is poor due to the high thermal resistance, and the effect of improving the output due to the reduction of interface defects is small. Therefore, the present invention is more applicable. It is effective.

The film formed by the electron cyclotron resonance plasma deposition method is highly dense and can obtain a thermal conductivity almost equal to the original thermal conductivity of the material of the film.
It is possible to suppress the temperature rise on the end face of the resonator and improve the optical output and reliability.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

The semiconductor laser device according to the first embodiment of the present invention will be described along with its manufacturing process. A perspective view of the semiconductor laser device is shown in FIG.

As shown in FIG. 1, n-Ga _{1 -z 1} Al _{z 1} A is formed on an n-GaAs substrate 1 by a metal organic chemical vapor deposition method.
s Lower clad layer 2 (thickness dc = 1700 to 2300nm, 0.55 ≦ z1
≦ 0.7), i-In _0.49 Ga _0.51 P lower optical waveguide layer 3 (thickness
db = 110 nm), In _x3 Ga _1-x3 As _1-y3 P _y3 quantum well active layer 4 (thickness da = 8 nm), i-In _0.49 Ga _0.51 P upper optical waveguide layer 5 (thickness db = 110 nm), p-Ga _{1-z 1} Al _{z 1} As upper first cladding layer 6 (thickness dc = 110 nm), p-In _0.49 G
a _0.51 P etching stop layer 7, p-Ga _{1- z 1} Al _{z 1} As
Upper second cladding layer 8 (thickness dc = 1700 to 2000 nm, 0.55 ≦ z1
≦ 0.7), and the p-GaAs contact layer 9 are grown in this order. Subsequently, an insulating film (not shown) is formed.
Next, by normal lithography, a stripe with a width of about 30 to 250 μm is formed with a width of 10 μm parallel to the peripheral portion continuous with the stripe.
The striped insulation film is removed, and wet etching is performed using this insulation film as a mask to form p-In _0.49 G
It was removed to the top of a _{0. 51} P etching stopper layer 7 to form a ridge stripe. An etching solution containing sulfuric acid and hydrogen peroxide solution is used as the etching solution. This automatically stops etching on the p-In _0.49 Ga _0.51 P etching stop layer 7. After removing the insulating film, a new insulating film 10 is formed, the insulating film 10 on the ridge stripe is removed by the ordinary lithography, the p-side electrode 11 is formed, and the substrate thickness is 100 to 150 μm. Until the board
Polishing 1 is performed to form the n-side electrode 12.

Regarding the wavelength band λ (nm) in which the semiconductor laser device produced as described above oscillates, In _x3 Ga
_1-x3 As _1-y3 P _y3 The composition of the quantum well active layer is 0 ≦ x3 ≦ 0.5
And by setting 0 ≦ y3 <0.5, control in the range of 750 <λ <1100 is possible.

The growth method of each layer may be a molecular beam epitaxial growth method using a solid or gas as a raw material. Although the above structure consists of a semiconductor layer grown on an n-type substrate, a p-type substrate may be used, in which case the conductivity of the semiconductor layer need only be reversed.

Next, the sample, which has been subjected to the electrode formation as described above, has a cavity length of 0.9 mm and a bar length of about 10 to 20 (mm) in a direction in which the (100) plane of GaAs is exposed in the atmosphere. Cleavage to expose the light emitting end face.

Next, the bar-shaped sample is set in a jig capable of coating in the atmosphere, set in an electron cyclotron resonance (ECR) sputtering apparatus, and evacuated.
An oxide for the purpose of controlling the reflectance on the two end faces is formed in a film formation mode in a film thickness corresponding to the desired reflectance. A low reflection film made of Al ₂ O ₃ is formed on one end face of the resonator.
14 is formed to have a wavelength of λ / 2 (reflectance 32%, 809 nm). In addition, on the opposite end face, a highly reflective film 13 (a semiconductor layer side is made of Al ₂ O ₃
/ SiO ₂ / Al ₂ O ₃ / SiO ₂ / Al ₂ O ₃ / SiO ₂ /
Al ₂ O ₃ / SiO ₂ / Al ₂ O ₃ / SiO ₂ ) is formed.
The Al ₂ O ₃ film of the first layer from the laminate side of the Al ₂ O ₃ made of a low reflection film 14, and the high-reflection film 13, the surface roughness is formed by 3nm or less. Incidentally, the Al ₂ O ₃ film of the first layer from the laminate side of the Al ₂ O ₃ film, and the high reflection film 13 of the low reflection film 14 is confirmed to be formed in good reproducibility similar surface roughness There is.

Here, FIG. 2 shows a structural diagram of the ECR sputtering apparatus. This ECR sputtering device is equipped with a sample table 32 and
A vacuum chamber 31 provided with 33, introducing pipes 34a and 34b with a valve for introducing a reaction gas into the vacuum chamber 31, a first target 35 and a second target 36, and the target using an ion beam for the sample stage. Electromagnetic coils 37 and 38 for accelerating to 32 and 33 respectively, and μ wave waveguide 39 and
40 and RF power sources 41 and 42. When forming a film, for example, ECR plasma is generated by introducing Ar gas or O ₂ gas and μ wave into the vacuum chamber 31. This plasma is accelerated toward the sample stage by the electromagnetic field generated by the electromagnet coil. The accelerated plasma deposits a voltage-applied target or its oxide on the sample.

Next, a bar-shaped sample having a reflectance control layer formed thereon is cleaved to have a width of 500 to 600 μm to manufacture a semiconductor laser device. Then, the p-side of the semiconductor laser device is placed on the heat sink. As for the heat sink, Ni plating (5
μm) on top of which Ni (50-150 nm), Pt (5
0 to 200 nm) and In (3.5 to 5.5 μm) are vapor-deposited in the order of description on at least four times the area of the bonding surface of the semiconductor laser device. 180 ~ 220 ℃ heat sink
Is heated in the temperature range of 1 to melt In and bond.

Next, a semiconductor laser device according to the second embodiment of the present invention will be described. A perspective view of the semiconductor laser device is shown in FIG.

As shown in FIG. 3, the semiconductor laser device according to the present invention has an n-Al _0.52 Ga _0.48 As lower cladding layer 32 (concentration 1 × 10 ¹⁸ cm ⁻³ , layer thickness 2.0) on an n-GaAs substrate 31. μm), n or i-InGaAsP optical waveguide layer 33 (layer thickness 50 nm), i-In _0.2 Ga _0.8 A
s Compressive strain quantum well active layer 34 (layer thickness 7 nm), i-InGaAsP optical waveguide layer 35 (layer thickness 50 nm), p-In _0.49 Ga _0.51 P low concentration upper first
Cladding layer 36 (Zn concentration 5 × 10 ¹⁷ cm ^-3 , layer thickness 5 nm), p-In
_0.49 Ga _0.51 P High concentration upper first cladding layer 37 (Zn concentration 1 ×
10 ¹⁸ cm ^-3 , layer thickness 0.2 μm), p-InGaAsP etching stop layer 38 (layer thickness 5 n) formed in a region other than the current injection region.
m) and n-InGaP current blocking layer 39 (concentration 5 × 10 ¹⁷ c
m ^-3 , layer thickness 1.0 μm), p-Al _0.47 Ga _0.53 As upper second cladding layer 40 (concentration 1 × 10 ¹⁸ cm ^-3 , layer thickness 1.5 μm), and p-Ga
The As contact layer 41 (concentration 5 × 10 ¹⁹ cm ⁻³ , layer thickness 0.1 μm) is laminated, and the insulating film 43, the p-side electrode 44, and the substrate 31 are formed in a region other than the current injection region. It is provided with an n-side electrode 45 formed on the back surface.

A low reflection film 46 made of an Al ₂ O ₃ film having a film thickness of λ / 4 is provided on one end face of the resonator so that the reflectance is 3% at an oscillation wavelength of 980 nm, and the other end face is oscillated. Al ₂ O having a thickness of λ / 4 so that the reflectance is 95% at a wavelength of 980 nm
₃ / TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂ / S
It is provided with a high-reflection film 47 composed of 10 layers composed of iO ₂ / TiO ₂ / SiO ₂ / TiO ₂ . Al ₂ O ₃ of low reflection film 46
The first layer from the side of the laminated body of the film and the high reflection film 47
The surface roughness of the ₂ O ₃ film is 3 nm or less. Also, width 2.0 μm
Two grooves 42 for reducing parasitic capacitance are provided on both sides of the light emitting region stripe at a distance of 100 μm. The resonator length is 1.2 mm and the oscillation wavelength is 980 nm.
This semiconductor laser device is also mounted on the heat sink as in the first embodiment.

With respect to the semiconductor laser device of the present invention, the relationship between the surface roughness of the reflective film, the thermal conductivity and the light output was examined.

First, the relationship between the surface roughness of the reflective film and the thermal conductivity was examined. FIG. 4 is a graph showing the relationship between the surface roughness of the reflective film and the thermal conductivity. The vertical axis of FIG. 4 is the thermal conductivity of sapphire, which is the normalized thermal conductivity of the Al ₂ O ₃ film. Al ₂ with different surface roughness on GaAs substrate
O ₃ film (however, with oscillation wavelength λ890nm, film thickness λ / 2)
Evaporation, magnetron sputtering and ECR sputtering 3
A plurality of samples formed by one forming method were prepared and used for evaluation. The thermal conductivity of the Al ₂ O ₃ film was measured by PIT-1 manufactured by Vacuum Riko. For the surface roughness, a 100 μm square area was measured by an atomic force microscope, and the Peak-Valley maximum value within the measurement range was adopted.

As shown in FIG. 4, as the surface roughness decreases, the thermal conductivity almost equal to that of sapphire is obtained. That is, as the surface roughness decreases, higher thermal conductivity is obtained, and it can be seen that the temperature rise of the end face can be suppressed well. Furthermore, of the three film forming methods,
The film formed by ECR sputtering has the highest film-forming ion energy and a low film-forming operating gas pressure of 10 ^-2 Pa.
It can be seen that the surface roughness is small and high thermal conductivity is obtained.

Next, the relationship between the surface roughness of the reflective film and the maximum light output was examined. FIG. 5 shows the measurement results of the semiconductor laser device of the present invention (the device using the InGaAsP active layer), and FIG. 6 shows the measurement results of the semiconductor laser device of the comparative example. The semiconductor laser device of the present invention uses the semiconductor laser device according to the first embodiment. Especially, the stripe width is about 50 μm and the oscillation wavelength is 809 nm.
The composition ratio of each layer is z1 = 0.64, x3 = 0.12 and y3 = 0.24,
A plurality of elements each having the reflective film formed by the three forming methods of vapor deposition, magnetron sputtering, and ECR sputtering were manufactured to be an evaluation element. The semiconductor laser device of the comparative example has the layer structure of the semiconductor laser device according to the first embodiment, which includes Ga _1-z Al _z As (0 <z <0.3) in the active layer, and particularly has an oscillation wavelength of 809 nm. Therefore, the device has z = 0.09. Further, the maximum light output was the peak value of the light output when the drive current was increased, as shown in FIG.
Note that the the Al ₂ O ₃ film of low reflection film 14, the Al ₂ O ₃ film which is the first layer of a semiconductor of a laminated body side of the high reflection film 13 has a similar surface roughness.

In the semiconductor laser device of the present invention, as shown in FIG. 5, as the surface roughness of the film becomes smaller,
It can be seen that the maximum light output is high. Further, also in the semiconductor laser device of the comparative example, as shown in FIG.
It can be seen that the maximum light output increases as the surface roughness of the film decreases. That is, it is considered that the decrease of the thermal conductivity leads to the improvement of the maximum light output. In particular,
In the semiconductor laser device of the present invention, the effect of reducing the surface roughness is remarkable. In a semiconductor laser device having an Al-based active layer, non-radiative recombination due to an interface defect is still dominant as a cause of the decrease in maximum optical output, but the recombination speed is small and the effect of improving the optical output by reducing the interface defect is small. In the semiconductor laser device of the present invention in which the active layer does not contain Al, it is considered that the decrease in heat conduction directly leads to the improvement of the maximum light output. Thus, it can be seen that the surface roughness correlates with the thermal conductivity of the film itself, and accordingly correlates with the maximum light output.

From the above, as a method of increasing the thermal conductivity and suppressing the temperature rise of the end face, providing a highly dense passivation film is more effective in the case of a semiconductor laser device having an active layer containing no aluminum. Became clear. Therefore, the semiconductor laser device of the present invention,
Since the highly dense passivation film having a surface roughness of 3 nm or less is provided, the thermal output is high and the optical output reaching COD is high, so that high optical output and reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing an ECR sputtering device.

FIG. 3 is a perspective view showing a semiconductor laser device according to a second embodiment of the present invention.

FIG. 4 shows various passivation film forming methods,
Graph showing the relationship between the surface roughness of the film and the normalized thermal conductivity

FIG. 5 is a graph showing the relationship between the film surface roughness and the maximum optical output when the active layer is InGaAsP.

FIG. 6 is a graph showing the relationship between the film surface roughness and the maximum optical output when the active layer is AlGaAs.

FIG. 7 is a graph showing the relationship between drive current and optical output.

[Explanation of symbols]

1 n-GaAs substrate 2 n-Ga _1-z1 Al _z1 As lower cladding layer 3 i-In _0.49 Ga _0.51 P lower optical waveguide layer 4 In _x3 Ga _1-x3 As _1-y3 P _y3 quantum well active layer 5 i- In _0.49 Ga _0.51 P upper optical waveguide layer 6 p-Ga _1-z1 Al _z1 As upper first clad layer 7 p-In _0.49 Ga _0.51 P etching stop layer 8 p-Ga _1-z1 Al _z1 As upper second clad layer 9 p-GaAs contact layer 10 insulating film 11 p-side electrode 12 n-side electrode 13 high reflection film 14 low reflection film

Claims (4)

[Claims] 1. A semiconductor laser device comprising a semiconductor laminated body including a light emitting layer and a waveguiding layer, and a passivation film made of an oxide on a cavity facet of the laminated body, wherein the laminated body side of the passivation film is provided. A semiconductor laser device, wherein the surface roughness of the first layer is 3 nm or less. 2. The semiconductor laser device according to claim 1, wherein at least the first layer of the passivation film is made of at least one oxide of Al, Si, Ti, and Ta. 3. The semiconductor laser device according to claim 1, wherein the light emitting layer and the waveguide layer are made of a semiconductor containing no Al. 4. The semiconductor laser device according to claim 1, wherein at least the first layer of the passivation film is formed by an electron cyclotron resonance plasma deposition method.