JP2002198615A - Semiconductor laser device - Google Patents

Abstract

(57) [Problem] To provide a semiconductor laser device having excellent temperature characteristics and high reliability even at the time of high-output operation and high-temperature operation. SOLUTION: An n-type GaAs substrate 11 has an n-type AlG
aInP clad layer 12, AlGaInP light guide layer 1
3, multiple quantum well active layer 15, AlGaInP light guide layer 16, p-type AlGaInP lower cladding layer 17, p-type GaInP etching stop layer 18, p-type AlGaI
nP upper cladding layer 20, p-type GaInP intermediate band gap layer 21, p-type GaAs contact layer 22, n-type G
It has an aAs current blocking layer 27. p-type AlGaIn
The P lower cladding layer 17 has a Be concentration of AlGaIn
The end on the side of the P light guide layer 16 is 1.8 × 10 ¹⁸ cm ⁻³ ,
1.0 × 10 ¹⁸ cm ⁻³ at the end of the etching stop layer 18
Therefore, the threshold current is relatively low, and the device has good reliability even at high temperatures and high output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device, and more particularly, to an AlGaInP (aluminum-gallium-indium-phosphorus) semiconductor laser device.

[0002]

2. Description of the Related Art In recent years, AlGaInP-based semiconductor laser devices have begun to be used as light sources for recording and reading in optical information processing systems such as magneto-optical disks and optical disks.

When a semiconductor laser device is used as a light source for such an optical information processing system, it is necessary to shorten the oscillation wavelength in order to increase the density of information. Requires higher laser oscillation power. In particular, in order to shorten the wavelength or increase the output of an AlGaInP-based semiconductor laser device, it is important to control the overflow of electrons from the active layer to the cladding layer. When the overflow of electrons is large, the operating current when the temperature of the semiconductor laser element rises increases, the power consumption increases, and the reliability decreases. because,
This is because when the operating current increases and the current density increases, deterioration of the active layer and the like is promoted.

Therefore, in order to obtain high reliability in a high-output semiconductor laser device, it is necessary to reduce the operating current at high temperatures.

FIG. 8A is a sectional view showing the structure of a conventional AlGaInP semiconductor laser device. This semiconductor laser device has an n-type GaAs (gallium arsenide) substrate 11.
1, an n-type AlGaInP cladding layer 112, an undoped GaInP active layer 113, a p-type AlGaInP lower cladding layer 114, a p-type GaInP etching stop layer 115, a p-type AlGaInP upper cladding layer 116,
After sequentially stacking a p-type GaInP intermediate band gap layer 117 and a p-type GaAs contact layer 118,
AlGaInP upper cladding layer 116, p-type GaIn
The P intermediate band gap layer 117 and a part of the p-type GaAs contact layer 118 are removed by photolithography to form a stripe-shaped ridge portion 120, and thereafter, the n-type GaAs is embedded so as to fill the ridge portion 120.
The current block layer 122 is formed. Each of these layers is formed by MBE (Molecular Beam Epitaxy) or MOCVD.
(Organic metal vapor phase epitaxy). This semiconductor laser device has a p-type A
In order to control the overflow of electrons to the 1GaInP lower cladding layer 114, the p-type AlGaInP lower cladding layer 114 is doped with P as an impurity, and
The barrier effect against electrons from the InP active layer 113 is enhanced.

FIG. 8B is a band diagram showing the vicinity of the GaInP active layer 113 of the semiconductor laser device when the p-type AlGaInP lower cladding layer 114 is not doped with an impurity. As shown in this band diagram, in the conduction band C, an overflow of electrons mainly occurs from the GaInP active layer 113 toward the p-type AlGaInP lower cladding layer 114.

FIG. 8C is a band diagram near the active layer when the p-type AlGaInP lower cladding layer 114 is doped with P (phosphorus). As shown in this band diagram, the Fermi level F approaches the valence band B side due to the P dopant, so that the p-type AlGaIn
Since the level of the P lower cladding layer 114 on the side of the conduction band C is increased, the overflow of electrons from the active layer 113 is reduced. In this way, the operating current when the temperature of the semiconductor laser device rises is reduced, and the temperature characteristics of the semiconductor laser device are improved.

Conventionally, AlGaI as shown in FIG.
In an nP-based semiconductor laser device, Zn (zinc) is used in addition to P as a dopant for a p-type cladding layer. However, when Zn is used as a dopant for the p-type cladding layer, the semiconductor laser
When manufacturing by the CVD method, diffusion of Zn from the p-type cladding layer to the active layer poses a problem, as pointed out in Japanese Patent Application Laid-Open No. Hei 4-74487. In addition, Japanese Unexamined Patent Application Publication No.
As pointed out in -317385,
At the time of crystal growth of the current block layer and thereafter, if necessary, at the time of crystal growth of the contact layer and the like, the high temperature at the time of crystal growth causes pile-up of Zn in the active layer. However, there is a problem that the Zn causes an increase in an oscillation threshold current and a deterioration in temperature characteristics. The cause of these problems is that, in order to prevent the overflow of electrons from the active layer, Z-type
n is highly doped.

Therefore, recently, as a dopant for the p-type cladding layer, B has been
It has been proposed to use e (beryllium). For example, B is applied to the cladding layer made of GaAs by MBE.
When e is doped, even if the doping is high in density, problems such as segregation and irregular diffusion of Be from the cladding layer do not occur (M. Ilelems: J. App.
l. Phys. Vol. 48, 1278, (197
7)). Even when AlGaInP is doped with Be as described above, problems such as segregation and diffusion of Be from AlGaInP are substantially the same as in the case of GaAs.

Hereinafter, A having the same structure as that of FIG.
In a 1GaInP-based semiconductor laser device, p-type Al
The result of analyzing the segregation and diffusion of Be when the GaInP lower cladding layer 114 is doped with Be is shown. The structure of the semiconductor laser device used in this analysis is shown in FIG.
Since this is the same as the semiconductor laser device shown in FIG. 8A, the description will be made using the reference numerals shown in FIG.

FIG. 9 shows that an n-type AlGaInP cladding layer 112 is formed on an n-type GaAs substrate 111 in the process of fabricating a semiconductor laser device by the MBE method.
FIG. 9 is a diagram showing the Be concentration around the undoped GaInP active layer 113 when layers up to an As contact layer 118 are sequentially stacked. The Be concentration was analyzed by SIMS analysis (secondary ion mass spectrometry). FIG.
The periphery of the P active layer 113, that is, Be is 1 × 10 ¹⁸ c
a p-type AlGaInP lower cladding layer 114 doped at a concentration of m ^-3 , a non-doped GaInP active layer 113 having a thickness of 1000 angstroms in contact with the p-type AlGaInP lower cladding layer 114;
4 shows a Be concentration profile in the n-type AlGaInP cladding layer 112 in contact with the nP active layer 113. As can be seen from FIG. 9, the concentration of Be is p-type AlG
aInP lower cladding layer 114 to GaInP active layer 1
It decreases sharply toward 13. Therefore,
It can be said that the diffusion of Be from the p-type AlGaInP lower cladding layer 114 during the crystal growth by the MBE method has almost no problem. The diffusion of Be from the p-type AlGaInP lower cladding layer 114 is much less than when Zn is used as a dopant.

FIG. 10 shows that the p-type AlGaInP upper cladding layer 116, the p-type GaInP intermediate band gap layer 117 and the p-type GaAs contact layer 118 are etched to form a ridge portion 120, and then crystallized by MBE. FIG. 9 is a diagram showing the Be concentration near the GaInP active layer 113 when the ridge 120 is grown and the current blocking layer 122 is embedded. The Be concentration was analyzed by the CV method (capacitance-voltage method). FIG.
0, the vicinity of the GaInP active layer 113, that is,
P-type AlGaInP doped with Be at 1 × 10 ¹⁸ cm ⁻³
The Be concentration in the lower cladding layer 114 and the non-doped GaInP active layer 113 adjacent to this layer are shown. As can be seen from FIG. 10, the pile-up of Be hardly occurs in the GaInP active layer 113 even during the second crystal growth.

From the above analysis results, when the semiconductor laser device is stacked by the MBE method, even if the p-type AlGaInP lower cladding layer 114 is doped with Be as a p-type dopant at a high density,
The diffusion and pile-up of e do not occur, and as a result, a semiconductor laser device having good temperature characteristics can be obtained.

[0014]

However, the above-mentioned p
Increasing the Be concentration in the lower AlGaInP cladding layer 114 improves the temperature characteristics of the semiconductor laser device, but increases the threshold current at room temperature (for example, 25 ° C.).

This problem is caused by the fact that the p-type AlGaInP lower cladding layer 114 is highly doped with Be, so that the electric resistivity of the p-type AlGaInP lower cladding layer 114 is reduced. That is, p-type AlG
In the aInP lower cladding layer 114, as shown by the arrow A, the current spreads not only immediately below the ridge portion 120 but also to the left and right sides below the ridge portion 120 in FIG. It will flow. As a result, the threshold current increases.

Therefore, if Be is doped into the p-type AlGaInP lower cladding layer 114 at a high concentration, the temperature dependence is eliminated due to a decrease in overflow.
Since the threshold current at room temperature increases, the operating current at a high temperature eventually increases, and the operating current of the semiconductor laser device at a high temperature and a high output remains high. That is, high temperature,
There is a problem that the reliability of the semiconductor laser device at the time of high output cannot be improved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser device having excellent temperature characteristics and high reliability even at high output operation and high temperature operation.

[0018]

According to a first aspect of the present invention, there is provided a semiconductor laser device having at least a first cladding layer of a first conductivity type, an active layer, and a second conductive layer. In a ridge guide type semiconductor laser device in which a second clad layer of a second type, an etching stop layer of the second conductivity type, and a third clad layer of the second conductivity type are laminated, the second clad layer is It is characterized in that a portion close to the active layer has a higher impurity concentration than other portions.

According to the above structure, the second clad layer has a higher impurity concentration in the portion near the active layer than in the other portions. Electrons are prevented from overflowing. On the other hand, the other portion of the second cladding layer, that is, the portion far from the active layer has a lower impurity concentration than the portion near the active layer. Thereby, the second
Current diffusion hardly occurs in the portion of the cladding layer far from the active layer. Therefore, an increase in the reactive current that does not contribute to laser oscillation is prevented, so that an increase in the threshold current of the semiconductor laser element is suppressed, and an increase in the operating current of the semiconductor laser element is prevented. As a result, there is no overflow from the active layer to the second cladding layer even at high power and high temperature, and the threshold current does not increase, so that a highly reliable semiconductor laser device can be obtained.

In one embodiment, a light guide layer is provided between the active layer and the second clad layer.

According to the above embodiment, the active layer and the second
Since the light guide layer is provided between the first and second cladding layers, the effect of confining light in the active layer is improved, and stable laser oscillation can be obtained.

In one embodiment, at a portion of the second cladding layer where the concentration of impurities is close to the active layer of the second cladding layer, overflow of carrier electrons from the active layer to the second cladding layer is caused. The concentration is such that current diffusion does not occur in the portion of the second cladding layer far from the active layer, as well as the concentration that does not occur.

According to the above embodiment, in the second clad layer, the concentration of the impurity in the portion close to the active layer is such that the overflow from the active layer does not occur,
The portion far from the active layer has a concentration that does not cause current diffusion. Therefore, the overflow from the active layer to the second cladding layer and the current diffusion in the second cladding layer are prevented, the rise of the threshold current is prevented, and the low threshold current is obtained even at high temperature and high output. Laser oscillates,
A semiconductor laser device having good reliability is obtained.

In one embodiment, the second cladding layer
The impurity concentration is close to the active layer of the second cladding layer.
1.8 × 10 in part¹⁸cm^-3And 3.0 ×
10 ¹⁸cm^-3And the first of the second conductivity type
In the portion of the cladding layer far from the active layer, 1.0 ×
10¹⁸cm^-3Less than and 0.5 × 10¹⁸cm^-3Is over
You.

According to the above embodiment, the concentration of the impurity is 1.8 × 10 ¹⁸ cm ⁻³ or more and 3.0 × 10 ¹⁸ cm ³ in the portion of the second cladding layer close to the active layer.
Since it is ^-3 or less, overflow from the active layer to the second cladding layer is reliably prevented. Here, if the concentration of the impurity is less than 1.8 × 10 ¹⁸ cm ⁻³ , the overflow of electrons from the active layer increases. If the concentration of the impurity is higher than 3.0 × 10 ¹⁸ cm ⁻³ , the impurity diffuses to the active layer and the threshold current increases.

Further, the concentration of the impurity is 1.0 × 10 4 in the portion of the second clad layer far from the active layer.
^{Since it is 18} cm ⁻³ or less and 0.5 × 10 ¹⁸ cm ⁻³ or more, current diffusion of the second cladding layer is reliably prevented.
Here, if the concentration of the impurity is higher than 1.0 × 10 ¹⁸ cm ⁻³ , the current diffusion will increase sharply. Also,
If the concentration of the impurity is less than 0.5 × 10 ¹⁸ cm ⁻³ , the overflow of electrons from the active layer as the whole second cladding layer is insufficiently prevented.

The distribution pattern of the impurity concentration in the second cladding layer may have any shape such as a linear shape or a stepped shape between a portion close to the active layer and a portion far from the active layer. You may do it.

In a semiconductor laser device according to one embodiment, the second cladding layer is made of p-type AlGaInP.
The active layer is made of GaInP or AlGaInP, and the impurity of the second cladding layer is Be.

According to the semiconductor laser device of the above embodiment, the second cladding layer is made of p-type AlGaInP, the active layer is made of GaInP or AlGaInP, and the impurity of the second cladding layer is Be. In addition, a semiconductor laser device having good temperature characteristics can be obtained with almost no diffusion and pile-up of the dopant from the cladding layer to the active layer at a high temperature.

Further, the method of manufacturing a semiconductor laser device according to the second invention is characterized in that at least a first cladding layer of the first conductivity type, an active layer, and a second cladding layer of the second conductivity type are formed on the substrate. A method of manufacturing a ridge guide type semiconductor laser device in which an etching stop layer of a second conductivity type and a third cladding layer of a second conductivity type are stacked, wherein the second cladding layer is formed in a portion close to the active layer. Is formed by MBE, gas source MBE, or CBE (chemical beam epitaxy) so as to have a higher impurity concentration than the other portions.

According to the method of manufacturing a semiconductor laser device of the second aspect of the present invention, the second clad layer is formed such that, in a portion close to the active layer, the concentration of impurities in the other portion of the second clad layer is lower. Since it is manufactured to have a high impurity concentration, overflow from the active layer to the second cladding layer is prevented. Further, since the second clad layer is manufactured so as to have a lower impurity concentration in another part of the active layer than in a part of the second clad layer close to the active layer, Current diffusion in other parts of the active layer is prevented. As a result, a semiconductor laser device having a relatively low threshold current and a high reliability without increasing the threshold current even at high temperatures and high powers can be manufactured by the MBE method or the gas source MBE.
Can be relatively easily manufactured using a conventional manufacturing apparatus by the CBE method.

In the present specification, the first conductivity type means p-type or n-type. The second conductivity type means n-type when the first conductivity type is p-type and p-type when the first conductivity type is n-type.

[0033]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a ridge guide type semiconductor laser device according to an embodiment of the present invention.

In this semiconductor laser device, an n-type GaAs substrate 11 is provided with an n-type n-type first cladding layer.
-Type AlGaInP cladding layer 12, AlGaInP light guide layer 13, multiple quantum well active layer 15, AlGaIn
P light guide layer 16, p-type AlGaInP lower cladding layer 17 as a second conductivity type second cladding layer, p-type GaInP etching stop layer 18 as a second conductivity type etching stop layer, and second conductivity type second cladding layer. 3, a p-type AlGaInP upper cladding layer 20, a p-type GaInP intermediate band gap layer 21, and a p-type GaAs
The s contact layer 22 is laminated. The above p-type AlG
aInP upper cladding layer 20, p-type GaInP intermediate band gap layer 21, and p-type GaAs contact layer 22
Form a stripe-shaped ridge portion 25, and fill the ridge portion 25 with an n-type GaAs current block layer 27.
Are formed.

This semiconductor laser device is manufactured as follows.

First, as shown in FIG.
An n-type AlGaInP cladding layer 1 is formed on an As substrate 11.
2, AlGaInP light guide layer 13, multiple quantum well active layer 15, AlGaInP light guide layer 16, p-type AlGa
InP lower cladding layer 17, p-type GaInP etching stop layer 18, p-type AlGaInP upper cladding layer 2
0, p-type GaInP intermediate band gap layer 21 and p
The GaAs contact layer 22 is sequentially stacked by the MBE method.

The multiple quantum well active layer 15 is formed of G
It has a multiple quantum well structure in which three aInP well layers and four AlGaInP barrier layers are stacked.

The n-type AlGaInP cladding layer 12 and the p-type AlGaInP lower and upper cladding layers 1
7 and 20 show that the composition is (AlyGa _(1-y) ) _x In.
_(1-x) P (x = 0.5, y = 0.7).

Next, p-type depositing an Al ₂ O ₃ film on the GaAs contact layer 22, mask layer 29 is patterned with this the Al ₂ O ₃ film by photolithography in stripes in FIGS. 2 (a) To form Using the mask layer 29 as a mask, wet etching is performed to form the contact layer 2.
2. The left and right sides of the intermediate band gap layer 21 and the p-type upper cladding layer 20 in FIG.
A ridge 25 as shown in FIG. 2B is formed. In the above wet etching, the etching is surely stopped by the p-type GaInP etching stop layer 18 whose etching rate is much lower than that of the p-type AlGaInP upper cladding layer 20.

Thereafter, as shown in FIG.
By the method, an n-type GaAs current blocking layer 27 is formed on both sides of the ridge 25, and an n-type GaAs polycrystalline layer 30 is formed on a mask layer 29 made of an Al ₂ O ₃ film.

Next, a photoresist 32 is applied on the n-type GaAs current blocking layer 27 and the n-type GaAs polycrystalline layer 30 shown in FIG.
An opening 33 is provided by photolithography in FIG.
(D), the n-type GaAs polycrystal 30 is exposed.

Subsequently, as shown in FIG. 4E, n-type Ga is formed by selective etching using a sulfuric acid-based etching solution.
After removing only the As polycrystal 30 and exposing the Al ₂ O ₃ film 29, the photoresist 32 is removed by ashing.

Thereafter, A is etched using a hydrofluoric acid-based etching solution.
The l ₂ O ₃ film 29 is removed by etching to obtain the semiconductor laser device shown in FIG.

Finally, electrodes (not shown) are formed on the upper surface of the contact layer 22 and the lower surface of the substrate 11 in FIG. 1, respectively, to complete a semiconductor laser device.

When the above semiconductor laser elements are stacked by the MBE method, the following doping is performed. That is, when forming the n-type AlGaInP cladding layer 12, AlGaInP is crystal-grown and doped with Si as an n-type dopant. p-type AlGaI
When forming the nP lower and upper cladding layers 17 and 20, AlGaInP is crystal-grown and doped with Be as a p-type dopant. In particular, the p-type A
When forming the lGaInP lower cladding layer 17, Be
Is made the density profile shown in FIG. FIG. 5 shows a p-type AlGaInP lower cladding layer 17.
, Etching stop layer 18 and p-type AlGaInP
FIG. 4 is a diagram showing the concentration of Be in the upper cladding layer 20; As shown in FIG. 5, the Be concentration of the p-type AlGaInP lower cladding layer
The side edge is set to 1.8 × 10 ¹⁸ cm ⁻³ , which is the highest, and is lowered toward the active layer etching stop layer 18 side.
^Make it ¹⁸ cm ^-3 . The Be concentration of the p-type AlGaInP upper cladding layer 20 is set to a constant concentration of 1.3 × 10 ¹⁸ cm ⁻³ .

The p-type AlGaInP lower cladding layer 1
7, a method of forming the Be concentration profile shown in FIG. 5 will be described below.

In the MBE method, a dopant contained in a cell is heated in an ultra-high vacuum to form a vapor-phase dopant.
A predetermined material is doped with the vapor-phase dopant by growing crystals together with the predetermined material. Therefore, by controlling the temperature of the cell in which the dopant is heated, the concentration of the dopant in a predetermined material can be adjusted. FIG. 6 shows that when the dopant is Be, Be
Is a graph showing the concentration of Be doped into AlGaInP with respect to the temperature of the cell in which is heated. The vertical axis represents the Be concentration (number of molecules / c) in AlGaInP.
m ⁻³ ), and the horizontal axis is the reciprocal of the temperature of the Be cell (K ⁻¹ ).
It is.

As shown in FIG. 6, in order to make the Be concentration of AlGaInP 1.8 × 10 ¹⁸ cm ^-3 , the reciprocal of the cell temperature is 9.31 × 10 ^-4 / K, that is, the cell temperature is 8
It needs to be 01 ° C. In addition, Be of AlGaInP
In order to make the concentration 1.0 × 10 ¹⁸ cm ⁻³ , the cell temperature needs to be 780 ° C.

Therefore, B in the AlGaInP layer
In order to make the density profile of e as shown in FIG. 5, the following is performed. That is, at the start of the growth of the p-type AlGaInP lower cladding layer, the temperature of the Be cell is set to 801 ° C., and the temperature of the cell is lowered as the growth time elapses. The cell temperature is brought to 780 ° C. Where p-type A
The lower cladding layer 17 of lGaInP has a thickness of 0.17 μm.
When AlGaInP is set to grow at a growth rate of 1 μm per hour, p-type AlGaInP
The time required for forming the P lower cladding layer 17 is 10
The time becomes 12 minutes, and the temperature change of the Be cell can be sufficiently followed.

The temperature control of the Be cell uses a thermoelectric device installed in the cell and a temperature controller based on PID (proportional operation, integral operation, differential operation; Proportional, Integral, Derivative) control.

The p-type AlGa
The Be concentration of the InP lower cladding layer 17 was changed to AlGaIn
In P optical guide layer 16 side edge to 1.8 × 10 ¹⁸ cm ^-3, the active layer etching stop layer 18 is lowered with the toward the side, the active layer etching stop layer 18 side end 1.0 × 10 ¹⁸ cm ^-3 .

The semiconductor laser device having the above-described structure and p-type Al
With respect to the semiconductor laser device of the comparative example in which only the Be concentration in the GaInP lower cladding layer was different, an experiment on the temperature dependence of the threshold current and the like was performed.

The semiconductor laser device of the comparative example is a p-type A
Except for the Be concentration in the lGaInP lower cladding layer,
It has the same configuration as the semiconductor laser device of FIG. Therefore, the semiconductor laser device of the comparative example will be described below using the reference numerals of the semiconductor laser device of FIG.

The semiconductor laser device of the comparative example is a p-type A
The Be concentration of the lGaInP lower cladding layer 17 is
The Be concentration of the lGaInP upper cladding layer 20 is made the same. As the semiconductor laser device of the comparative example, the above B
e concentration is 1.3 × 10 ¹⁸ cm ⁻³ (Comparative Example 1), 1.5
× 10 ¹⁸ cm ^-3 (Comparative Example 2), and 1.8 × 10 ¹⁸ c
Three types of semiconductor laser devices of m ⁻³ (Comparative Example 3) are set.

For the semiconductor laser device of the above embodiment and the semiconductor laser devices of Comparative Examples 1, 2, and 3, the threshold current I _th (mA) and the operating current I _{op at} operating temperatures of 25 ° C. and 60 ° C. (MA) and the characteristic temperature T
₀ (K) was calculated. Table 1 summarizes the results.

Note that the characteristic temperature T ₀ is a value representing the degree of increase in the threshold current with respect to the temperature rise, and the characteristic temperature T ₀
Is larger, the ratio of the rise of the threshold current to the rise of the temperature is smaller. That is, it can be said that the larger the characteristic temperature T ₀ is, the lower the temperature dependency of the threshold value is. The characteristic temperature (T ₀ )
It is determined from the following equation (1).

[0058]

I _th (60 ° C.) / I _th (25 ° C.) = Exp ((60−25) / T ₀ ) (1) where I _th (60 ° C.) is a threshold value at 60 ° C. The current (mA), I _th (25 ° C.) are the threshold current (mA) at 60 ° C., and T ₀ is the characteristic temperature (K).

[0059]

[Table 1]

Further, based on the results shown in Table 1, the threshold current I _th (mA) at the operating temperature of 25 ° C. was obtained for the semiconductor laser devices of this embodiment and Comparative Examples 1, 2, and 3.
And the operating current I _op (mA) at an operating temperature of 60 ° C.
And the characteristic temperature T ₀ (K) are shown in FIGS. 7 (a), (b),
A graph is shown in (c).

Table 1 and FIGS. 7 (a), (b),
From (c), regarding the characteristic temperature of the semiconductor laser device, the present embodiment is 45.0K and the comparative example 3 is 46.0K,
Since the characteristic temperatures are substantially the same, it can be said that all the semiconductor laser elements have low temperature dependence. The semiconductor laser devices of Comparative Examples 2 and 3 have characteristic temperatures of 42.0K and 46.0K, which are relatively high and have little temperature dependence. However, since the semiconductor laser devices of Comparative Examples 2 and 3 have comparatively large 25 ° C. threshold currents of 73.0 mA and 81.0 mA, the 60 ° C. threshold currents are also 168.0 mA and 18.0 mA.
It becomes as high as 73.4 mA. This is because, in the semiconductor laser devices of Comparative Examples 2 and 3, the p-type AlGaInP lower cladding layer 17 has a relatively high Be concentration, and the concentration is uniform in all parts of the p-type AlGaInP lower cladding layer 17. caused by. On the other hand, since the semiconductor laser device of the present embodiment has the Be concentration profile shown in FIG. 5, the characteristic temperature is as high as 45.0 K, the temperature dependency is small, and the threshold current at 25 ° C. is as small as 68.0 mA. , 60 ° C. threshold current is also as small as 148.0 mA. That is, the semiconductor laser device of the present embodiment has a small operating current even at the time of high temperature and high output, and has high reliability.

In the semiconductor laser device of the above embodiment, Be of the p-type AlGaInP lower cladding layer 17 is
The concentration is set to 1.8 × 10 ¹⁸ cm ⁻³ at the end of the AlGaInP light guide layer 16, and is reduced as it goes toward the active layer etching stop layer 18, and becomes 1.0 at the end of the active layer etching stop layer 18. × 10 ¹⁸ cm ^-3
The portion on the AlGaInP light guide layer 16 side is 1.8 × 10
¹⁸ cm ⁻³ , and the portion on the active layer etching stop layer 18 side is 1.0 × 10 ¹⁸ cm ⁻³ , the p-type AlGaI
The distribution shape of the Be concentration in the nP lower cladding layer 17 may be, for example, a step shape instead of a straight line.

In the semiconductor laser device of the above embodiment, the multiple quantum well active layer 15 has a multiple quantum well structure, but may have a single quantum well structure or a normal double heterostructure.

The semiconductor laser device according to the above-described embodiment includes the p-type AlGaInP upper cladding layer 20 and the p-type GaIn
The ridge portion 25 composed of the P intermediate band gap layer 21 and the p-type GaAs contact layer 22 is
The semiconductor laser device is a refractive index-guided semiconductor laser device buried in 7 and includes at least an active layer and a p-type clad layer and an n-type clad layer which are stacked so as to sandwich the active layer and have a larger band gap than the active layer. Other structures may be used as long as the semiconductor laser device has a double hetero junction structure.

Further, the semiconductor laser device of the present invention is not limited to the above-mentioned materials.
1GaInN, the active layer may be a blue semiconductor laser such as GaInN, and the cladding layer may be InGaAs.
P (or AlGaInNAs or AlGaIn
Sb), the active layer is made of InGaAsP (or GaIn
A long-wavelength semiconductor laser device such as NAs or GaInSb) may be used, and needless to say, various materials can be changed without changing the gist of the present invention.

Although the semiconductor laser device of the above embodiment is formed by crystal growth by the MBE method, it may be formed by a gas source MBE method, a CBE method, or the like.

In the semiconductor laser device, the first conductivity type is n-type and the second conductivity type is p-type. However, the first conductivity type is p-type and the second conductivity type is n-type. You may.

[0068]

As is clear from the above, according to the semiconductor laser device of the first invention, in the ridge guide type semiconductor laser device, the second cladding layer of the second conductivity type has a portion close to the active layer. Since the active layer has a higher impurity concentration than the other portions, the second conductive type second conductive type
Since it is difficult for electrons to overflow into the cladding layer and for current diffusion to a portion remote from the active layer, the first conductive type of the second conductivity type can be removed from the active layer at high power and high temperature.
An overflow to the cladding layer can be prevented, and a rise in the threshold current can be prevented, so that a highly reliable semiconductor laser device can be obtained.

Further, since the light guide layer is provided between the active layer and the second clad layer, the effect of confining light in the active layer can be improved and a stable laser oscillation semiconductor laser device can be obtained.

In the second cladding layer, the portion where the impurity concentration is close to the active layer is a concentration at which overflow from the active layer does not occur, and the portion far from the active layer is the second cladding layer. Since the concentration is such that current diffusion does not occur, overflow from the active layer to the second cladding layer and current diffusion in the second cladding layer can be prevented, and a low threshold value is obtained even at high temperatures and high output. Laser oscillation can be performed with current, and a semiconductor laser device having good reliability can be obtained.

Further, the impurity concentration of the second cladding layer
Degree in the portion of the second cladding layer closest to the active layer.
And 1.8 × 10¹⁸cm^-3Above and 3.0 × 10¹⁸
cm ^-3And the activity of the second cladding layer
In the part farthest from the layer, 1.0 × 10¹⁸cm^-3Less than
Lower and 0.5 × 10¹⁸cm^-3Above
From the layer to the second cladding layer
And the current diffusion of the second cladding layer is ensured.
Can be prevented.

The second cladding layer is made of p-type AlG
aInP, and the active layer is made of GaInP or Al.
Since the second cladding layer is made of GaInP and the impurity of the second cladding layer is Be, the diffusion and pileup of the dopant from the cladding layer to the active layer at a high temperature is almost eliminated, so that a semiconductor laser device having good temperature characteristics can be obtained. it can.

Further, according to the method of manufacturing a semiconductor laser device of the second invention, the second cladding layer is formed such that a portion near the active layer has a higher impurity concentration than other portions. Since the method includes a step of forming by the MBE method, the gas source MBE method, or the CBE method, the threshold current is relatively low, and the threshold current does not increase even at a high temperature and a high output. A semiconductor laser device having high reliability can be manufactured relatively easily using a conventional manufacturing apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram showing a semiconductor laser device according to an embodiment of the present invention.

FIGS. 2A and 2B are diagrams illustrating a process of manufacturing the semiconductor laser device illustrated in FIG.

FIGS. 3 (c) and 3 (d) are views showing a manufacturing process of the semiconductor laser device following FIG. 2 (b).

FIG. 4E is a diagram showing a manufacturing step of the semiconductor laser device following FIG. 3E.

FIG. 5 shows a p-type AlGaInP lower cladding layer 17;
FIG. 5 is a diagram showing the concentration of Be dopant in the etching stop layer 18 and the p-type AlGaInP upper cladding layer 20.

FIG. 6 is a graph showing the concentration of Be doped into AlGaInP with respect to the temperature of a cell for heating Be in the MBE method.

FIG. 7 shows the threshold current I at an operating temperature of 25 ° C. for the semiconductor laser devices of this embodiment and Comparative Examples 1, 2, and 3.
_th (mA) and the operating current I _{op at} an operating temperature of 60 ° C.
(MA) and a characteristic temperature T ₀ (K) in a graph.

FIG. 8A is a diagram showing a conventional semiconductor laser device, and FIG. 8B is a band diagram in a case where doping is not performed on a p-type AlGaInP lower cladding layer 114. (c) is a band diagram in the case where p-type AlGaInP lower cladding layer 114 is doped with P.

FIG. 9 shows a conventional semiconductor laser device,
FIG. 6 is a diagram showing the Be concentration around the GaInP active layer 113 when the layers 1 to the contact layer 118 are stacked by the MBE method.

FIG. 10 shows a conventional semiconductor laser device using MBE.
FIG. 9 is a diagram showing the Be concentration in the vicinity of the GaInP active layer 113 when the current blocking layer 122 is formed by embedding the ridge 120 by the method.

[Explanation of symbols]

 Reference Signs List 11 n-type GaAs substrate 12 n-type AlGaInP cladding layer 13 AlGaInP light guide layer 15 multiple quantum well active layer 16 AlGaInP light guide layer 17 p-type AlGaInP lower cladding layer 18 p-type GaInP etching stop layer 20 p-type AlGaInP upper cladding layer 21 p -Type GaInP intermediate band gap layer 22 p-type GaAs contact layer 25 ridge 27 n-type GaAs current block layer

Claims (6)

[Claims] 1. A method according to claim 1, wherein at least a first conductive type first substrate is provided on the substrate.
Guide-type semiconductor laser in which a cladding layer of the following type, an active layer, a second cladding layer of the second conductivity type, an etching stop layer of the second conductivity type, and a third cladding layer of the second conductivity type are laminated. In the device, a portion of the second cladding layer close to the active layer has a higher impurity concentration than other portions. 2. The semiconductor laser device according to claim 1, further comprising a light guide layer between said active layer and said second cladding layer. 3. The semiconductor laser device according to claim 1, wherein the concentration of the impurity in the second cladding layer is from the active layer to the second cladding in a portion of the second cladding layer near the active layer. A semiconductor laser device having a concentration that does not cause overflow of carrier electrons into the layer and a concentration that does not cause current diffusion in a portion of the second clad layer far from the active layer. 4. The semiconductor laser device according to claim 3, wherein
Therefore, the concentration of the impurity in the second cladding layer is lower than the second cladding layer.
In the portion of the lad layer close to the active layer, 1.8 × 10¹⁸
cm^-3Above and 3.0 × 10¹⁸cm^-3If the following
In the portion of the second cladding layer far from the active layer,
And 1.0 × 10 ¹⁸cm^-3Less than and 0.5 × 10¹⁸cm
^-3A semiconductor laser device characterized by the above. 5. The semiconductor laser device according to claim 1, wherein the second cladding layer is made of p-type AlGaInP, the active layer is made of GaInP or AlGaInP, A semiconductor laser device wherein the impurity in the cladding layer is Be. 6. A method according to claim 1, wherein at least a first conductive type first substrate is provided on the substrate.
Ridge-type semiconductor laser in which a first cladding layer, an active layer, a second cladding layer of the second conductivity type, an etching stop layer of the second conductivity type, and a third cladding layer of the second conductivity type are stacked. In the device manufacturing method, the second cladding layer may be formed by an MBE method, a gas source MBE method, or a C source method so that a portion near the active layer has a higher impurity concentration than other portions.
A method for manufacturing a semiconductor laser device, comprising a step of forming by a BE method.