JPH0344085A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To increase only the quantity of the intrusion of light to the n-type clad layer side having low resistivity without augmenting the distance of the intrusion of light to a p-type InGaAlP clad layer having high resistivity, and to reduce the optical density of an active layer by forming an optical guide layer between the active layer and an n-type clad layer. CONSTITUTION:Since an optical guide layer 12 having a refractive index higher than clad layers 11, 14 is formed brought into contact with an active layer 13, light is mainly wave-guided in the optical guide layer 12. Consequently, the optical density of the active layer 13 is made smaller than normal double hetero-structure having no optical guide layer having the same active-layer thickness by approximately forty %, and a COD optical output is increased by approximately one and a half times. Since the intrusion of light to the outside of the active layer 13 is extended to the optical guide layer 12 and n clad layer 11 side, the sum total of the thickness of the optical guide layer 12 and the clad layer 11 on the n side must be increased to 1.5mum in order to prevent the augmentation of absorption loss in a GaAs substrate 10.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser used as a light source for optical information processing equipment, optical measurement equipment, etc.
The present invention relates to a semiconductor laser device that uses color-based materials and emits color-based light.

(Prior art) In recent years, InGaAIP red lasers with an oscillation wavelength in the 0.6 μm band have been commercialized, and are used as light sources for optical information processing equipment such as optical disk devices and laser beam printers, as well as for barcodes and It is expected that it will have a wide range of applications as a light source for readers, optical measurement equipment, etc. I nGaA I
Increasing the output power of P-based red lasers is important in expanding the range of their applications.

For example, for writing to an optical disk device, an optical output of at least 20 mW or more is required. Also,
High light output enables laser beam printers to print at high speeds. In general, using a laser that can provide a high optical output increases the tolerance to loss in the optical system, making it possible to simplify the optical system and reduce its cost.

However, it has been difficult to increase the output of InGaAlP-based red lasers due to the following reasons. - As an example, a transverse mode control type ridge stripe structure suitable for an optical disk device or a light source for laser beam plinking as shown in FIG. 9 will be explained. In the figure, 90 is an n-GaAs substrate, 91 is an n-1nGaAIP cladding layer, 93 is an InGaP active layer, and 94 is a p-1nG
aAIP cladding layer, 95 nGaAs current blocking layer, 9
6 indicates a p-GaAs contact layer, and 97.98 indicates an electrode.

In this ridge stripe type InGaAlP laser,
As with other laser structures, the maximum optical output is due to the so-called instantaneous optical damage caused by the reabsorption of light at the laser cavity facets.
age : COD ), and when the active layer thickness is 0.06 μm, its value is lO ~ 15 m
It was about W.

One way to improve the optical output that causes COD is to reduce the optical density of the active layer 93 by reducing the thickness of the active layer 93 and increasing the amount of light seeping into the cladding layers 91 and 94. It is valid. In fact, when the thickness of the active layer 93 was reduced to 0.04 .mu.m, the light output for generating COD was improved to 20 mW or more, and the maximum light output was achieved for a glass can.

However, by using InGaAlP-based materials,
The following problems arose.

When the thickness of the active layer 93 is made as thin as 0.04 μm, the distance for light to seep out from the active layer 93 also becomes long.
The cladding layer 9
It is necessary that the thickness of 1.94 be 1.2 μm or more (if the active layer thickness is 0.06 μm, the cladding layer thickness may be 0.8 μm).

However, the p-type cladding layer I n0.5 (Ga+-x A lx ) 0.5
Since the mobility of holes in P (x≧0,6) is small, its resistivity is extremely high at 1 to 2 ΩCl even if the hole concentration is about 5 x 10" cm. When Zn, which has good controllability, was used as a dopant, the upper limit of the hole concentration was about 5 x IQ17 cm.As a result, the Joule heat generation during operation increases due to an increase in the electrical resistance of the element. In the device with a cladding layer thickness of 1.2 μm, the maximum oscillation temperature decreased to 50 to 60°C (the maximum oscillation temperature of the device with a cladding layer thickness of 0.8 μm was 80°C or higher). This value is completely insufficient for practical use, considering the margin for internal temperature of devices such as optical disk devices and laser beam printers.

(Problem to be Solved by the Invention) Conventionally, when the active layer is made thinner in order to improve the optical output that causes COD, the cladding layer (especially the p-cladding layer) has to be made thicker. Then, there is a problem that the series resistance of the element increases and the maximum oscillation temperature decreases. For this reason, it has been difficult to realize a high-output InGaAlP-based red semiconductor laser device with practically sufficient temperature characteristics.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a transverse mode-controlled InGaAlP semiconductor laser device that can obtain high optical output and has good temperature characteristics. It is in.

[Structure of the Invention (Means for Solving the Problems) The gist of the present invention is to provide an InGaAlP red light emitting semiconductor laser device without increasing the distance of light seepage into the p-type InGaAlP cladding layer with high resistivity. The purpose of this invention is to reduce the light density of the active layer by increasing only the amount of light seeping into the n-type cladding layer, which has a low resistivity.

That is, the present invention provides a double heterostructure on a GaAs substrate, in which an active layer made of InGaA I P or InGaP, which is lattice matched to GaAs, is sandwiched between p-type and n-type InGaA I P cladding layers, and In a semiconductor laser device in which a cap layer made of GaAs or InGaP is provided, an InGaA I P layer having a refractive index smaller than that of the active layer and larger than that of the cladding layer is disposed between the active layer and an n-type cladding layer. A light guide layer is formed, and a p-type cladding layer is formed thinner than an n-type cladding layer.

Further, the present invention provides a semiconductor laser device having a ridge structure in which n-type I n0.5 (Ga
+-1A lz ) 0,5P cladding layer.

n-type 1 n0.5 (Ga+-w A 1w ) 0
．． P light guide layer, I no5 (Ga+-x Alx
)0. s P active layer and p-type I n0.5 (Ga+
-y A ly ) 0.5 The P cladding layer is sequentially deposited, provided that 0≦x<w<y, z≦1), and a striped ridge is formed in the p-type cladding layer, and the side surface of this ridge is forms an n-type GaAs current blocking layer, and p-type ■no, 5G a 0.
5p or p-type GaAs cap layer is formed.

In the above semiconductor laser device, the In composition in each layer is 0.5, which is a value that perfectly lattice matches GaAs, but it does not necessarily have to match this value;
It may deviate somewhat from this value as long as crystal growth is possible with lattice matching with s.

(Function) According to the present invention, the light guide layer provided on the n-type cladding layer side in contact with the active layer increases the amount of light seeping into the n-type cladding layer side, reducing the optical density of the active layer. Therefore, it is possible to improve the COL and J optical outputs that limit the maximum optical output of the laser, and it is possible to increase the output of the laser. Also, since the distance of light seeping into the p-type cladding layer does not increase, there is no need to increase the thickness of the p-type cladding layer, which has high resistivity, and there is no need to increase the thickness of the p-type cladding layer, which prevents deterioration of temperature characteristics due to an increase in the electrical resistance of the element. do not have.

Therefore, high power InGaAlP with good temperature characteristics
This makes it possible to realize a red-based laser. Furthermore, for the above reasons, even if the thickness of the active layer is reduced, there is no need to increase the thickness of the p-type cladding layer, which has high resistivity. It is also possible to improve the performance.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 shows an InGaAl film according to a first embodiment of the present invention.
1 is a cross-sectional view showing a schematic structure of a P-based semiconductor laser. In the figure, 10 is an n-GaAs substrate, and on this substrate 10, n -I n0.5 (Gao3A 10.7 )0
5P cladding layer 11 (impurity concentration n −4X 1011
0l7', thickness 1μm), n -I n0.5 (Ga0.s A 10.5
) 0.5 P light guide layer 1.2 (n = 4
1011017a, thickness 0.5 μm), undoped I
no5Ga0. P active layer 13 (thickness 0.06 μm), p-I nO,s (Ga0.3 A 10.7 )
0. s P Clarado layer 14 (p = 4 X], 01
7cm', thickness 0.8IIm), and n7GaA
s Current blocking layer 15 (n = 2 Xl018cm
, 0.7 μm thick) were sequentially grown. A stripe-shaped opening is provided in the current blocking layer 15, and a p-GaAs contact layer 16 (p=2×1018 cm−3, thickness 3 μm) is grown on the current blocking layer 15 so as to fill the opening. There is. Then, an n-side electrode 17 is formed on the back surface of the substrate 10, and a p-side electrode 1 is formed on the contact layer 16.
8 is formed.

In the semiconductor laser configured in this manner, the light guide layer 12 is present in contact with the active layer 13 and has a refractive index higher than that of the cladding layer 11.14, so light is mainly guided through the light guide layer 12. . Therefore, in this example, the optical density of the active layer J3 is approximately 40% compared to the case of a normal double heterostructure without an optical guide layer having the same active layer thickness.
The COD light output was improved by about 1.5 times. Also,
Since light seeps out of the active layer 13 toward the light guide layer 12 and the n-cladding layer 11, in order to prevent an increase in absorption loss in the GaAs substrate 10, the light guide layer 12 on the n-side
It is necessary to increase the total thickness of the cladding layer 11 to 1.5 μm. However, the resistivity of n-1nGaAIP is
Since the resistivity of p-1nGaAIP is about 171O,
The increase in element resistance due to this was negligible.

Furthermore, since the band gap difference between the active layer 13 and the optical guide layer 12 is sufficiently large, the temperature characteristics of this laser do not deteriorate, and the maximum oscillation temperature is 70°C or higher, which is a value sufficient for practical use. It was done.

Increasing the amount of light seeping toward the n-cladding layer 11 side through the light guide layer 12 results in suppressing an increase in the distance of light seeping toward the p-cladding layer 14 side. Therefore, even if the thickness of the active layer 13 is made thinner (for example, 0.04 μm), there is no need to make the p-cladding layer 14 thicker. Therefore, it is possible to further improve the optical output by making the active layer 13 thinner.

FIG. 2 is a sectional view showing a schematic structure of a second embodiment of the present invention. In this embodiment, the present invention is applied to a transverse mode controlled InGaA IP laser having a ridge stripe structure.

In the figure, 20 is an n-GaAs substrate, and on this substrate 20, n I n0.5 (Ga0.: + A I 0.y
) 0. q P Clarado layer 21 (n w4 X10
17 cm-1 thickness 1 μm), n I n0. (Ga0
．． A 10.5 )'0.5 P light guide layer 22 (n
= 4 x 10"am-3, thickness 0.5μm),
2 Undoped In, 5Ga, , P active layer 23 (thickness 0
．． 06 μm), and p I n0.5 (G a0.3 A I 0.
7) 0. s P Clarado layer 24 (n = 4 X101
7 cm-, thickness 0.8 μm) were successively grown. A part of the p-Clarad layer 24 is etched halfway to form a striped ridge portion. The bottom width of this ridge portion is 5 μm.

An n-GaAs current blocking layer 25 (n
=2X10I8cm-, thickness 1μm) was grown,
In addition, p-G
aAs contact layer 26 (p = 2 x 1018c
m-3, thickness 3 μm) was grown and formed. and,
An n-side electrode 27 is formed on the back surface of the substrate 20, and a p-side electrode 28 is formed on the contact layer 26.

As with the previous example, the laser of this example also has a
The COD optical output was improved by about 1.5 times, and a maximum output of 20 mW or more was obtained. Moreover, the maximum oscillation temperature of 3 this laser was 80° C. or higher, which was good.

In a laser with a ridge stripe structure, as shown in this embodiment, the GaAs current blocking layer is usually n-type.
Formed on an n-type substrate.

This is because in n-type GaAs, the diffusion coefficient of holes, which are minority carriers generated by light absorption, can be made smaller than the thickness of the current blocking layer, so the minority carriers flow out of the current blocking layer and the potential of the current blocking layer increases. This is because the current blocking effect is not lost. In such a configuration, the current flows in a closed manner in the ridge made of the p-type cladding layer having high resistivity, so that the increase in device resistance due to the increase in the thickness of the p-type cladding layer is more significant. Therefore, by providing an optical guide layer on the n-type cladding layer side, the optical density of the active layer can be reduced without increasing the thickness of the p-type cladding layer, achieving good temperature characteristics and high output operation. This is particularly important for

By the way, when trying to obtain omic contact through GaAs for a semiconductor device having an active part made of InGaA IP, it is necessary to use InGaA IP and GaAs.
Good ohmic contact cannot be obtained with the device, and there is a risk that IH may deteriorate the A4+ characteristics of the device due to its operating voltage.

Therefore, in this example below, the In contact with the GaAs layer is
At least a part of the GaAlP layer has a carrier concentration of 5
Good ohmic contact is achieved by providing a high carrier concentration region with a thickness of 400 to 800 cm and a thickness of 1017 cm -3 or more.

FIG. 3 is a conceptual diagram showing a third embodiment of the present invention. 30 in the figure (is I rl+-x-y G<y A LX P
The layer 302 is a high gearia concentration region in the InGaAlP layer 301, and 303 is a GaAs layer. All layers have the same conductivity type, and p-type is shown here. It is important that the InGaAlP layer 301 is lattice-matched to GaAs, especially in light emitting devices, because it can be used as an epitaxially grown layer without impairing crystallinity.

An example of a composition x', y that does not meet these conditions is 5 x+y=0.5 It is.

Now, it has been experimentally found that good current-voltage characteristics between the GaAs layer 303 and the InGaAlP layer 301 depend largely on the carrier concentration p and thickness d of the high carrier concentration region 302. FIG. 4 shows the injection current density 1 at the interface between the GaAs layer 303 and the high carrier concentration region 302 for the carrier concentration p in the high carrier concentration region 302.
It shows the magnitude of voltage drop at kA/cm-2. When p≧5×1017cttV”, there is no effect of voltage drop, and increases in operating voltage and heat generation are not a problem.However, when p>3×1019c
When the carrier concentration is as high as m-3, the number of defects formed in the high carrier concentration layer rapidly increases to 1, and in a continuous operation test at 50°C and 3 mW, it deteriorates in about 100 hours, and p≦3
The reliability was significantly inferior to the value of 1000 hours or more obtained at 1.019 cm-'. T)
< 3 x 10''cm', the effect of voltage drop was large, causing an excessive increase in operating voltage and heat generation6.

Furthermore, it has been found that such a voltage drop occurs even when the thickness d of the high carrier concentration region 302 is very thin. FIG. 5 shows a GaAs layer 303 carved to a thickness d of the high carrier concentration region 302 and an I
nGaA1! Injected current density between P layer 301: 1 kA
The figure shows the magnitude of the voltage drop at /cm-2.

When d < 400 Å, the voltage drop suddenly increases.

Further, even when d≧400λ, the voltage drop gradually increases due to an increase in series resistance due to an increase in layer thickness.

As described above, the GaAs layer 303 and ] nGaA ] P
The current-voltage characteristics between layer P and layer 1 are InGaA
The carrier concentration p is greatly influenced by the carrier concentration p of the high carrier concentration region 302 formed near the interface with the GaAs layer 303 in the IP layer SQL and the thickness d of that region.
It is necessary that p≧5Xi [l” cm−3 and the thickness d≧400λ. Also, regarding the carrier concentration p, the above problem occurs when p≧7 3 × 1019 cm ′, so p is 5 x 10"cm-3≦p≦3X]-0"
Cm-3 is preferable.

FIG. 6 is a fourth embodiment of the present invention, and is a sectional view showing a schematic structure of a semiconductor laser in which a GaAs layer is used as an ohmic contact layer and an InGaAlP layer is used as a cladding layer. 60 (in the figure) is an n-GaAs substrate, and on the substrate 601 there is an n-GaAs substrate.
I nGaA I P Clarad layer 602.1 nGaAI
P active layer 8H, p-1nGaA IP cladding layer 60
4, a double heterojunction serving as a light-emitting active part is formed. I)-I nGaA I P clarad layer 8
04, a p-InGaP cap layer 605, an n-G
An aAs current confinement layer 606 is formed.

The n-GaAs current confinement layer 606 is selectively removed in stripes, and the p-1nGaP cap layer 805 and n-
A p-GaAs ohmic contact layer 607 is formed on the GaAs current confinement layer 606. Each layer of the double heterojunction 8 and the p-1nGaP cap layer 605 are made of In, Ga, Ga, etc. so that the lattice constant is approximately equal to that of the substrate and the band gap energy of the cladding layers 802 and 604 is larger than that of the active layer 603. The composition of AI is set.

The width of the n-GaAs current confinement layer 606 selectively removed in stripes is 7 μm, and the resonator length is 300 μm. Here, the carrier concentration of the p I n G a P cap layer 605 is I x 10110 l8', and the thickness is 500
When set to λ, the oscillation threshold current in pulse operation of this semiconductor laser is 70 mA, and the oscillation threshold current in continuous operation of the device is 72 mA, which is the threshold for pulse operation due to heat generation. The change in current was very small. Furthermore, a maximum continuous oscillation temperature of 90°C was obtained. This is a p-GaAs layer p-1nGaP/p-1n
This is because there is no excessive voltage drop at the GaAIP hetero interface, and the operating voltage at the threshold is kept as low as 2.3V.

On the other hand, when the carrier concentration of the p-1nGaP key 1''7 layer 605 is set to 4X1017CI11-3, the operating voltage is extremely high, 3V, and the heat generated during continuous operation is also large. Threshold current is 77mA
This was a large value. The maximum continuous oscillation temperature was also as low as 60°C. This is a p-GaAs layer p-1nGaP
This is thought to be due to an excessive voltage drop at the /p-1nGaAIP heterointerface.

Further, even when the carrier concentration of the p-InGaP cap layer 605 is I x 1018c + Il-', when the thickness of the cap layer 605 is 250 mm, the operating voltage becomes very large, 3V, and accordingly, Heat generation during continuous operation was large, and the threshold current was a large value of 77 mA. The maximum continuous oscillation temperature was also as low as 60°C. Conversely, if the thickness of the p-1nGaP cap layer 605 is 1
When the thickness was about 000λ, the maximum continuous oscillation temperature was as low as 30° C. due to an increase in heat generation due to an increase in series resistance, an increase in threshold current due to current spread, and an increase in thermal resistance.

FIG. 7 shows the dependence of the maximum continuous oscillation temperature on the thickness d of the p-1nGaP cap layer 605.

0 When 400λ≦d≦800 people, the maximum continuous oscillation temperature is 8
A high value of 0° C. or higher was obtained, and the maximum continuous oscillation temperature suddenly decreased outside this range. In addition, especially 400λ≦d≦6
At 00λ, the maximum continuous oscillation temperature was 85° C. or higher, showing very good thermal characteristics.

FIG. 8 is a fifth embodiment of the present invention, and is a sectional view showing a schematic structure of a semiconductor laser in which a GaAs layer is used as an ohmic contact layer and an InGaAlP layer is used as a cladding layer. In the figure, 801 is an n-GaAs substrate, and on this substrate 801 is an n-1nGaAIP cladding layer 802.
AIP active layer 803, p-1nGaAIP
First cladding layer 804, p-1nGaA I
P etch stop layer 805. A double heterojunction portion, which is a light emitting active portion, is formed of a p-InGaAlP second cladding layer 806 having a striped and convex shape.

p-1n Ga A I P second cladding layer 806
A p-InGaP cap layer 807 is formed on the convex portion. An nGaAs current confinement layer 808 is formed in a portion of the p-1nGaAIP1 cladding layer 806 other than the convex portion. pInGaPInGa
On the P character and n-GaAs current confinement layer 808, there is a p-
A GaAs ohmic contact layer 809 is formed. In is used so that the photon constant of each layer of the double heterojunction and the p-1nGaP cap layer 807 is approximately equal to that of the substrate, and the band gap energy of the cladding layers 802, 804, and 808 is larger than that of the active layer 803.

The compositions of Ga and AI are set.

The stripe width was 5 μm and the length of each resonator was 300 μm.

The maximum continuous oscillation temperature of this semiconductor laser is p-InGaP
Depending on the carrier concentration and thickness of the cap layer 807, it was approximately equivalent to the device with the structure of the fourth example shown in FIG.

In addition, in the device of this structure, when forming the p-1nGaAIP cladding layer 806 having a striped and convex shape, the p-1nGaAIP cladding layer 806 is
It is necessary to selectively remove the −1nGaP cap layer 807 at areas other than the convex portions.

At this time, if a mixed solution of Br2, HBr, and H2O is used as a method of etching the p-1nGaP cap layer 807, the p-InGaP cap layer 807 is etched in the vicinity of the stripe.
Key t”yp layer 807 and pI n G a A, l
The etching rate of the P Clarad layer 806 tends to be partially large. Therefore, in order to achieve flat and good etching, it is desirable to reduce the thickness of the p-1nGaP cap layer 807 and to shorten the etching time for removing the p-1nGaP cap layer 807 as much as possible. At this time, the thickness of the p-1nGaP cap layer 807, which was flat and could be etched well, was 600 Å or less.

In addition, in the fourth and fifth embodiments, p-
Although a semiconductor laser using 1nGaP has been described, the cap layer may generally be made of InGaAlP.

At this time, if the energy gap of the cap layer is smaller than that of the cladding layer, the energy gap with the GaAs layer will be smaller, and ohmic characteristics can be easily obtained. Furthermore, by combining the third to fifth embodiments with the first or second embodiment, it is possible to realize a semiconductor laser that has the advantages of each of the three embodiments. Furthermore, the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As described in detail above, according to the present invention, by providing a light guide layer between the active layer and the n-type cladding layer, light can be directed to the p-type 1nGaAIP cladding layer with high resistivity. It is possible to reduce the optical density of the active layer by increasing only the amount of light seeping toward the n-type cladding layer, which has a lower resistivity, without increasing the seepage distance. Therefore, a high-output InGaAlP-based red semiconductor laser with good temperature characteristics can be realized, and its industrial effects are extremely large.

[Brief explanation of drawings]

FIG. 1 shows InGaAlP according to the first embodiment of the present invention.
2 is a cross-sectional view showing a schematic structure of a semiconductor laser according to a second embodiment of the present invention. FIGS. 3 to 5 are cross-sectional views showing a schematic structure of a second embodiment of the present invention.
FIG. 6 and FIG. 7 are diagrams for explaining the fourth embodiment of the present invention, and FIG. 8 is a diagram for explaining the fifth embodiment of the present invention. 9 are cross-sectional views showing a schematic structure of a transverse mode control type 1nGaAIP semiconductor laser having a conventional structure. 10.2O-n-GaAs substrate, 11.2l-n-1nGaAIP optical cladding layer, co-2
, 22-n-1nGaA IP light guide layer, 13,
23---1n GaP active layer, 14, 24
-p-1nGaAIP cladding layer, 15.25・-n-
GaAs current blocking layer, 16.26-=p-GaAs contact layer, 17.27...n-electrode, 18.28...p-electrode.

Claims (2)

[Claims] (1) On the GaAs substrate, In is lattice-matched to GaAs.
The active layer made of GaAlP or InGaP is p-type and n-type.
In a semiconductor laser device in which a double heterostructure sandwiched between two InGaAlP type cladding layers is provided, and a cap layer made of GaAs or InGaP is provided thereon, a layer between the active layer and the n-type cladding layer is provided from the active layer to the n-type cladding layer. InG has a small refractive index and a larger refractive index than the cladding layer.
1. A semiconductor laser device comprising an aAlP optical guide layer and a p-type cladding layer thinner than an n-type cladding layer. (2) n-type In_0_ provided on an n-type GaAs substrate
．． _5(Ga_1_-_zAl_z)_0_. _5P cladding layer (0<z≦1) and n-type In_0_. _5(Ga_1_-_wAl_w
)_0_. _5P light guide layer (0<w<z) and In_0_. _5(Ga_1_
−_xAl_x)_0_. _5P active layer (0≦x<w)
and p-type In_0_. which is provided on this active layer and has a striped ridge formed therein. _5(Ga_1_-_y
Al_y)_0_. _5P cladding layer (w<y≦1), an n-type GaAs current blocking layer formed on the side surface of the striped ridge of the p-type cladding layer, and an n-type GaAs current blocking layer provided on the top of the striped ridge of the p-type cladding layer. 1. A semiconductor laser device comprising a cap layer made of p-type GaAs or InGaP.