JPH05243669A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce a light absorption near an end face of a laser, to enhance an optical damage level and to raise an output of the laser by forming an asymmetrical SCH structure in which an optical guide layer of an n-type clad layer side is formed thicker than that of a p-type clad layer side. CONSTITUTION:The semiconductor laser element comprises a light-carrier isolating confinement structure in which an AlGaInP active layer 7 and both sides of the layer 7 provided on a semiconductor substrate 1 are held by an optical guide layer 8 made of AlGaInP having a larger band gap than the active layer. This structure is formed in an asymmetrical SCH structure in which a thickness of an n-type side guide layer is formed larger than that of a p-type side guide layer, a high refractive index layer 4 made of AlGaInP having a higher refractive index than that of the clad layer is provided in an n-type clad layer 3 and a refractive index of the layer 4 is set to the same degree as an average refractive index of the SCH structure having the layer 7 and an optical guide layer 6. A center of a waveguide mode can be shifted into the n-type side optical guide layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device used as a light source for optical information terminal equipment and the like, which has a low threshold current, a sufficiently high optical damage level, and a high reliability capable of stable high output operation. Semiconductor laser device of the present invention.

[0002]

2. Description of the Related Art The reason why the light output of an AlGaInP semiconductor laser is limited is that light absorption in the vicinity of the end face of the laser resonator generates heat and the end face of the resonator is destroyed by optical damage. Conventionally, in order to prevent damage to the laser end face due to optical damage, the active layer is thinned to increase the amount of light leaking into the cladding layer, and the optical density inside the active layer is reduced to suppress heat generation due to light absorption. Was taken. This is, for example, the case in the literature (Extended Abstracts of the 1991 Internat
ional Conference on Solid State Devices and Materia
ls, pp 114-116 (1991)).

[0003]

When the active layer is made thin in order to suppress the destruction of the end face due to optical damage, the electrons injected into the active layer are significantly leaked to the p-clad layer.
Thermal saturation of light output occurs. As a result, the temperature characteristics of the device deteriorate, and a problem arises in that good high temperature and high output characteristics cannot be obtained. In addition, when the active layer is thinned, the modes guided in the laser spread, so light absorption occurs in the GaAs buried layer, and the cladding layer is formed so that optical loss does not increase and the threshold current does not increase. It was necessary to make it 1.5 μm or more. However, it is difficult to increase the hole concentration in the AlGaInP quaternary mixed crystal having a large Al composition, and the p-type AlGaInP clad layer has a high resistivity and a low thermal conductivity. Therefore, if the thickness of the clad layer is increased by thinning the active layer, the device resistance and thermal resistance increase, and there arises a problem that deterioration of the oscillation characteristics of the device is promoted due to a temperature rise near the active layer.

[0004]

In the light guide layers provided on both sides of the active layer, the film thickness of the n-side guide layer is made larger than that of the p-side guide layer, or the light guide layer is provided only on the n-side. The above problem is solved by adopting a structure in which a high-refractive index layer having a refractive index similar to the average refractive index of the waveguiding layer including the active layer and the optical guide layer is provided inside the n-clad layer can do.

[0005]

In the conventional laser device having the DH structure or the SCH structure, the intensity distribution of the light guided inside the laser is as shown in FIG. Light is guided around the active layer having the largest refractive index, and the center of the guided mode in which the light intensity is maximum exists inside the active layer. Therefore, strong light absorption occurs at the same time as light emission due to stimulated emission, and it is difficult to suppress heat generation in the vicinity of the laser facet, and light damage easily occurs. On the other hand, when the structure according to the present invention is used, the light intensity distribution inside the laser is as shown in FIG. By making the SCH structure asymmetric and further providing a high refractive index layer inside the n-clad layer to form an asymmetrical waveguide structure, the center of the waveguide mode can be shifted to the inside of the n-side optical guide layer. However, the light is guided around the optical guide layer, which has a wide band gap and is transparent to the laser light. for that reason,
The optical confinement expressed by the optical confinement coefficient in the one-dimensional view to the active layer can be kept at the same level to reduce the optical absorption, and the heat generation due to the optical absorption near the laser facet can be reduced to reduce the optical damage. The level can be improved.

FIG. 4 shows a calculation example of the relationship between the film thickness d and the shift amount. The peak position of the guided mode gradually shifts as the film thickness d of the high refractive index layer increases. When the optical confinement in the high refractive index layer becomes stronger than the optical confinement in the active layer and the light guide layer at d = d _o , the position of the peak of the guided mode shifts into the high refractive index layer, and the shift amount ΔZ becomes unclear. It changes continuously. If d is further increased, the light confinement in the active layer becomes weaker, and ΔZ increases, and at the same time, the threshold current starts to increase. When the film thickness is made extremely large, the guided mode is distributed around the high refractive index layer, so that the overlap between the distribution of carriers confined in the active layer and the light intensity distribution is extremely reduced and sufficient optical The threshold current increases without gain. Further, with respect to the Al composition x of the high refractive index layer (Al _x Ga _1-x ) _0.5 In _0.5 P, the smaller the Al composition x, the higher the refractive index and the ΔZ changes greatly. From these, the range of the film thickness d of the high refractive index layer is set to Al so that the peak absorption amount ΔZ is set to 20 nm or more to reduce the light absorption and the threshold current density can be lowered.
Composition x, were set as follows: the active layer d _a and the light guide layer thickness d _g.

20 nm <d <d _a x x 10 + d _{g In} this range, the threshold current density of the laser device using the asymmetrical waveguide structure of the present invention has a threshold current density of _a DH structure laser with an active layer thickness d _a. It is possible to realize a laser device which does not exceed the current density and operates at a low threshold value and has a high optical damage level.

Further, using the structure of the present invention and providing a high refractive index layer to shift the waveguide mode to the n-clad layer side is also effective in reducing the element resistance. By shifting the waveguide mode to the n-clad layer side, light leakage to the p-clad layer is reduced, and even if the p-clad layer is thinned to 0.8 μm, the waveguide loss due to light absorption in the GaAs buried layer is reduced. No increase will occur. Since the p-clad layer having a high resistivity can be thinned while keeping the threshold current low, the device resistance and the thermal resistance can be reduced. Heat generation is suppressed by reducing element resistance,
In addition, since the heat in the vicinity of the active layer can be efficiently dissipated, it is possible to improve the high temperature and high output operation characteristics.

[0009]

The concrete structure of the semiconductor laser according to the present invention will be described below.

Embodiment 1 FIG. 1 is a configuration diagram showing an embodiment of a semiconductor laser device of the present invention. In this embodiment, the SCH structure is provided on the n-type GaAs substrate, and the high refractive index layer is provided inside the n-clad layer. First, the n-type is formed on the n-type GaAs substrate 1 by the MOCVD method.
GaAs buffer layer 2 (film thickness 0.5 μm), n-type (Al _0.7 Ga _0.3 ) _0.5 I
n _0.5 P clad layer 3 (film thickness 2.0 μm), n-type (Al _x Ga _1-x ) _0.5 In _0.5 P high refractive index layer 4 (film thickness 60 nm) with Al composition x 0.4, n
Type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P barrier layer 5 (film thickness 20 nm), undoped (Al _y Ga _1-y ) _0.5 In _0.5 P optical guide layer 6 (Al composition y = 0.4)
Undoped G with a thickness of 40 nm) and a thickness of 13 nm with 1.5% strain introduced.
a _0.31 In _0.69 P Active layer 7, undoped (Al _y Ga _1-y ) _0.5 In _0.5
P light guide layer 8 (Al composition y = 0.4 film thickness 5 nm), p-type (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P Clad layer 9 (film thickness 0.2 μm), p-type Ga _0.5 I
n _0.5 P Etch stop layer 10, p-type (Al _0.7 Ga _0.3 ) _0.5 In
_0.5 P clad layer 10 (film thickness 0.6 to 1.0 μm), p-type Ga _0.5 In
_{The 0.5} P buffer layer 11 and the n-type GaAs cap layer were sequentially stacked. Next, after depositing a SiO ₂ film (film thickness 0.2 μm), the SiO ₂ film was processed into a stripe shape by a photo process. This SiO ₂
Ga provided inside the cladding layer using the film stripe as a mask
_The cladding layer was selectively etched up to the _0.5 In _0.5 P layer etch stop layer 11. Next, the n-type GaAs current blocking layer 13
After the SiO ₂ and GaAs cap layers were removed, the p-type GaAs contact layer 14 was grown. Finally, after undergoing an electrode process on both p and n surfaces, the chip was cleaved.

As a result of measuring the characteristics of the manufactured device, the maximum optical output was 100 mW or more, and a laser device that stably operates in a single mode was obtained. The threshold current is 30-40mA,
No increase in the threshold current and no asymmetry in the far-field pattern due to the shift of the guided mode inside the laser to the n-clad layer side were observed. In addition, the propagation loss inside the laser does not increase even if the p-clad layer is thinned to 0.8 μm by shifting the waveguide mode, and the device resistance is kept as low as 4 to 5 Ω while maintaining good oscillation characteristics. I was able to.

Second Embodiment FIG. 2 is a configuration diagram showing a second embodiment of the semiconductor laser device of the present invention. This is a structure in which the high refractive index layer 4 in the first embodiment is replaced with a multiple quantum well structure 4 '. In the multiple quantum well structure, the GaInP well layer width L _z was 3 nm, the AlGaInP barrier layer width L _B was 5 nm, and eight wells were provided to form a high refractive index layer having a total film thickness of 59 nm. The other parts had the same structure as in the first embodiment, and a laser device was manufactured as a prototype.

If the Al composition x of the high refractive index layer is reduced, the refractive index can be increased, but if the Al composition is reduced, a deep well may be formed with respect to the carrier and the carrier may be trapped. Therefore, the quantum well effect is used to make the effective well depth shallow, and a multiple quantum well structure is used so that carriers are not accumulated in the high refractive index layer.

As a result of evaluating the prototyped device, a high optical output of 100 mW or more was obtained as in the first embodiment. Element resistance is as small as 4 to 5 Ω, and current due to carrier trapping −
No change in voltage characteristics was observed.

[0015]

EFFECT OF THE INVENTION An SC provided with light guide layers on both sides of the active layer.
In the H structure, the optical guide layer on the n-clad layer side has an asymmetrical SCH structure in which the optical guide layer is thicker than the optical guide layer on the p-clad layer side, and further, a high refractive index layer is provided in the n-clad layer. The center of the guided mode inside the laser was shifted to the n-clad layer side. As a result, it was possible to reduce the light absorption in the vicinity of the laser end face, raise the light damage level, and increase the output of the laser. In the conventional structure, 80
While the maximum light output at 40 ° C was 40 mW, it was possible to obtain a light output of 100 mW at a high temperature of 100 ° C by using the structure of the present invention. Further, since the waveguide mode is shifted to the n-clad layer side, most of the light is concentrated on the n-clad layer side, and the leakage of light to the p-clad layer is reduced. done. By reducing the thickness of the p-type AlGaInP clad layer, which has a relatively high resistivity, the device resistance was reduced, and the device resistance, which was about 10Ω in the past, could be halved to 4-5Ω. Further, since the p-cladding layer is provided with a laser stripe structure, it is preferable that the p-cladding layer be thin in order to manufacture the laser with high accuracy, and the laser manufacturing accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a structural diagram of a laser showing a first embodiment.

FIG. 2 is a structural diagram of a laser showing a second embodiment.

FIG. 3 is a conceptual diagram showing the operation of the laser according to the present invention.

FIG. 4 is an example of a calculation result of a relationship between a film thickness d, a peak shift amount ΔZ, and a threshold current density.

[Explanation of symbols]

1 ... n type GaAs substrate, 2 ... n type GaAs buffer layer, 3 ... n type
AlGaInP clad layer, 4 ... n-type AlGaInP high refractive index layer, 5 ...
n-type AlGaInP barrier layer, 6 ... Undoped GaInP light guide layer, 7 ... Undoped GaInP active layer, 8 ... Undoped GaInP
Optical guide layer, 9 ... p-type AlGaInP cladding layer, 10 ... p-type G
aInP etch stop layer, 11 ... p-type AlGaInP cladding layer 12, p-type GaInP buffer layer, 13 ... n-type GaAs current blocking layer, 14 ... p-type GaAs contact layer, 15 ... p-electrode, 16 ... n-electrode, 4 '... GaInP / AlGaInP multiple quantum well structure, ΔZ ... shift amount of peak position, d _a ... active layer film thickness, d _g ... optical guide layer film thickness, d _B ... barrier layer film thickness, d ... high refractive index layer film Thick.

Claims (7)

[Claims] 1. An AlGaInP active layer provided on a semiconductor substrate and AlGa having a band gap larger on both sides than the active layer.
Light-Carrier Separation and Confinement between the optical guide layers made of InP (hereinafter referred to as S
(Abbreviated as CH) structure, the thickness of the guide layer on the n side is set to p
The asymmetrical SCH structure is made thicker than the thickness of the guide layer on the side, a high refractive index layer made of AlGaInP having a higher refractive index than the cladding layer is provided inside the n cladding layer, and A semiconductor laser device having the same refractive index as that of an SCH structure including an optical guide layer. 2. The semiconductor laser device according to claim 1, wherein the semiconductor substrate material is GaAs, and (Al _x Ga _1-x )
_1-α In _α P GaAs with In composition α of 0.5 or more in the active layer
Introduce a compressive strain that causes lattice mismatch with the substrate and reduce the strain amount to 0.8.
It is characterized by being set in the range of up to 2.5%. 3. The semiconductor laser device according to claim 1, wherein the active layer structure is a double hetero structure.
terostructure: hereinafter abbreviated as DH), the active layer thickness d _a
10 ≤ d _a ≤ 40 nm or well width L in multiple quantum well structure
_z is 3 ≤ L _z ≤ 10 nm and total film thickness d _a is 20 ≤ d _a ≤ 50 nm
It is characterized by 4. An asymmetric SCH according to claim 1.
In the structure, the thickness of the light guide layer provided on the p-clad layer side is 10 nm or less, or the light guide layer is not provided on the p-side, and the light guide layer thickness d _g on the n-clad layer side is 10 nm to 10 nm.
The feature is that it is set to 0 nm. 5. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is provided inside an n-clad layer (Al _x Ga _1-x ).
_0.5 In _0.5 P The film thickness d of the high refractive index layer is defined as the Al composition of the high refractive index layer.
x, the film thickness d _{a of the} active layer and the film thickness d _g of the n-side light guide layer are set in a range of 20 nm <d <d _a · x · 10 + d _g . 6. The semiconductor laser device according to claim 1 or 5, wherein the high refractive index layer has a multiple quantum well structure, and the Al composition x of the high refractive index layer is the well layer and the barrier layer. It is characterized in that it is defined as an average composition. 7. The semiconductor laser device of the claims preceding claim, characterized in that the barrier layer thickness d _B provided between the high refractive index layer and the optical guide layer was in the range of 5nm~40nm ..