JPH0732286B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to an improvement of a semiconductor laser device having a built-in waveguide structure.

(Prior Art) With the opening of applications of semiconductor lasers as optical sources for optical discs such as digital audio discs 9DAD, video discs, document files and light sources for optical communication, mass production technology for semiconductor lasers is required. . Conventionally, the liquid phase epitaxial growth method (LPE method) by the stiding boat method has been used as a thin film multilayer heterojunction crystal manufacturing technology for semiconductor lasers.
The PE method has a limit in increasing the wafer area. For this reason,
Crystal growth techniques such as vapor phase epitaxy (MOCVD) and molecular beam epitaxy (MBE), which use an organic metal capable of epitaxial growth excellent in uniformity and controllability in a large area, are attracting attention.

Incorporated waveguide lasers that take advantage of the characteristics of the MOCVD method can be found in the literature (5th International Solid-State Devices / Materials, Conferences, Extended, Abstracts, p. 153, 198).
There is a semiconductor laser shown in Fig. 12 that was announced in (3rd year). In the figure, 51 is an N-GaAs substrate, 52 is an N-Ga _0.6 Al _0.4 As clad layer, 53 is a Ga _0.92 Al _0.08 As active layer, and 54 is P-Ga _0.6 A.
l _0.4 As clad layer, 55 N-Ga _0.6 Al _0.4 As current blocking layer (different layer), 56 P-Ga _0.78 Al _0.27 As first coating layer, 57 P-Ga _0.6 Al _0.4 As second coating layer , 58 are P-GaAs contact layers, and 59, 60 are metal electrode layers.

In this structure, the current blocking layer 55 of different conductivity type restricts the current injection into the active layer 53 in a stripe shape, and at the same time, the first coating layer close to the active layer 53 among the coating layers embedded in the stripe-shaped groove portion. By making the refractive index of 56 larger than that of the clad layer 54, the light exuding into the stripe-shaped groove is affected by the high-refractive-index layer and becomes higher in the area directly below the stripe-shaped groove in the horizontal direction to the bonding surface. Since a difference in refractive index is formed, light is confined in the horizontal direction.
The oscillation threshold of continuous oscillation at room temperature is as low as 40 [mA], and the optical output of 30 [mA] or more is obtained in the fundamental transverse mode oscillation.

The laser having the above structure is manufactured by the following steps. First, on a N-GaAs substrate 51 (Si-doped 1 × 10 ¹⁸ cm ^-3 ) with a plane orientation (100), a thickness of 1.5 [μmm] of N-GaAlAs is used.
Cladding layer 52 (Se-doped 1 × 10 ¹⁷ cm ^-3 ), thickness 0.08 [μ
m] undoped GaAlAs active layer 53, 1.0 [μm] thick P-GaAlAs cladding layer 54 (Zn-doped 7 × 10 ¹⁸ cm ⁻³ ) and 0.7 [μm] thick N-GaAlAs current blocking layer 55 (Se Dope 5 × 10 ¹⁸ cm ⁻³ ) is successively grown. Next, a photoresist is applied on the current blocking layer 55, and a width of 2 is applied to the resist.
A stripe-shaped window of [μm] is formed, and using this as a mask, the current blocking layer 55 and the clad layer 54 are partially etched to form a stripe-shaped groove. Then, after removing the resist, a P-GaAlAs first coating layer 56 having a thickness of 0.3 [μm], a P-GaAlAs second coating layer 57 having a thickness of 1.25 [μm] and a P-GaAlAs second coating layer 57 having a thickness of 5 [μm] are formed on the entire surface. A GaAlAs contact layer 58 (Zn-doped 5 × 10 ¹⁸ cm ⁻³ ) is grown and formed. Thereafter, a Cr-Au electrode 59 is deposited on the contact layer 58 by a normal electrode attaching process, and an Au-Ge electrode 60 is further deposited on the lower surface of the substrate 51 to obtain the structure shown in FIG. .

The MOCVD method was used for both crystal growth, and the second crystal growth was GaAlAs whose surface was once exposed to the air.
Growth on the plane. For this reason, it is difficult to grow by the LPE method, and the MOCVD method, which makes it easy to grow on the GaAlAs surface, can be manufactured with good controllability. In the case of the above parameters, the N-clad layer and P-
The specific resistance of the clad layer is 0.2 [Ωcm] and 0.06, respectively.
[Ωcm].

On the other hand, although the write-once type and rewritable type optical disk devices are being developed at a rapid pace, high output semiconductor lasers are used as the light source of these devices. In these devices, recording and erasing are performed with high output, but the output of the semiconductor laser is limited, and deterioration of the laser is more likely to occur when driven with higher output. Therefore, the collection rate of laser light is higher than that of read-only devices. Is increased. Therefore, when erasing the record,
A light output of ~ 30 [mW] and 0.8-1 [mW] will be used during playback, while a light output of 3-5 [mW] will be used for playback only.

Such a light source for an optical disc is required to have the following performance.

(1) Low threshold, low current drive (2) From low output during playback to high output operation during recording,
The transverse mode is the basic mode and a constant spot diameter can be obtained. (3) The beam can be narrowed down. Here, (1) is a characteristic required to secure the reliability of the laser. The characteristics (2) and (3) are particularly important performances related to the pit shape written on the disc and the error rate during reproduction.

The laser described above is capable of high-power operation and has a fundamental transverse mode oscillation, but the above performance has not been sufficiently satisfied. That is, as for the low threshold value, the threshold current of 10 to 20 [mA] is obtained in the buried type (BH) laser and the lateral junction type (TJS) laser, which have the same built-in waveguide structure. Laser is 40 [mA], twice as high. Regarding the transverse mode characteristics, the fundamental transverse mode oscillation was obtained up to 30 [mW] or more. However, when the dependence of the beam shape and the spot diameter on the optical output was examined, there was a problem especially at low output around 1 [mW]. It was found that the spot diameter was 1.2 to 1.5 times larger than that at the time of high output, and that the shape was likely to be separated and deformed due to the influence of both ends of the internal stripe. As a cause of characteristic differences and problems due to such a structure, compared to BH laser and TJS laser, the laser of the above structure is not well current confinement, the current is considerably along the junction surface. It is possible that it has spread.

To confirm this point, the measurement of the current dependence of the emission intensity distribution width, which reflects the current distribution in the active layer, is the 13th method.
It is a figure. According to this figure, the internal stripe width is 1.5 [μ
In contrast, in the case of low current injection, a current spread of 30 [μm] or more is generated, and it is understood that the current spread width is not yet stable particularly near 1 [mW] even when the threshold value is reached. Therefore, in the vicinity of 1 [mW], due to the influence of the current spread, the spot diameter becomes larger than that at the time of high output, and the influence of both ends of the stripe is also likely to occur. In such a mode, it is known that the imaging characteristics are deteriorated because the higher-order mode is included in the basic mode. In addition, it is conceivable that the threshold value may be higher than that of a BH laser or the like, which has a good current confinement, due to the large amount of reactive current.

In the case of a read-only optical disk device, such a characteristic uses an optical output of 3 [mW], and therefore has little effect to a certain extent. Since the light output of [mW] is used, it becomes a very big problem.

(Problems to be Solved by the Invention) As described above, conventionally, in the semiconductor laser having the built-in waveguide structure, the current confinement is not favorably performed, and the stable fundamental transverse mode is realized particularly near the oscillation threshold. It was difficult to do.

The present invention has been made in consideration of the above circumstances, and the purpose thereof is to make it possible to reliably produce a built-in waveguiding effect due to an effective refractive index difference, and to reduce the threshold value.
In addition, a stable current confining effect can be provided over a wide optical output range from near the oscillation threshold to high output operation, and particularly, a stable basic lateral operation is achieved from low output near the threshold to high output operation of 30 [mW] or more. It is to provide a semiconductor laser device that exhibits mode oscillation.

[Structure of the Invention] (Means for Solving the Problems) The essence of the present invention is that the coating layer has a layered structure of two layers or more, and a layer having a high refractive index is brought close to the active layer in the stripe. In a semiconductor laser that performs mode control while maintaining a sufficiently large effective refractive index just below the stripe, the current spread in the active layer is suppressed to a sufficiently small level, and a wide optical output range from near the oscillation threshold to high output operation is achieved. The purpose is to have a stable current constriction effect.
Further, in order to ensure this current constriction effect, it is necessary to optimize parameters such as the film thickness of the cladding layer and the specific resistance.

That is, the present invention has a double heterostructure part made of a compound semiconductor material, and on the clad layer on the side opposite to the substrate with respect to the active layer of this double heterostructure part, the conductivity type is different from that of the clad layer and the stripe shape is formed. In a heterojunction type semiconductor laser device in which a heterogeneous layer having a groove portion is formed, and a coating layer of the same conductivity type as the above-mentioned cladding layer is formed on the heterogeneous layer to provide a current constriction effect and a built-in waveguide effect, The heterogeneous layer is formed of a compound semiconductor material containing Al, the coating layer is formed of at least two layers, and the first coating layer closer to the active layer is a layer having a higher refractive index than the cladding layer, The second one that is farther from the active layer than the first coating layer
Is a layer having a smaller refractive index than the first coating layer, and the specific resistance ρ ₂ of the clad layer on the side opposite to the substrate with respect to the active layer and the film thickness d _{2 of the} clad layer are set as follows. Under The specific resistance ρ ₃ of the clad layer on the substrate side with respect to the active layer is set to 0.1 [Ωcm] or less.

In the above equation, W is the bottom width [cm] of the stripe-shaped groove in the different layer, h is the distance [cm] from the active layer to the first coating layer at the bottom of the stripe-shaped groove, and Δη _eff is the effective inside and outside of the stripe-shaped groove. Refractive index difference, D is spread in the direction parallel to the junction surface of the waveguide mode determined by the bottom width W of the stripe-shaped groove and the effective refractive index difference Δη _eff, and θ is the complement of the angle formed by the bottom of the stripe-shaped groove and the side surface. The angle and β are the current-voltage characteristics of the pn junction by I∝ex
Diode characteristic parameter, J, expressed as p (βV _j ), J
Each _th represents a threshold current density.

The internal stripe width W and the effective refractive index difference Δη
According to experiments by the present inventors, _eff is W in order to ensure that a stable fundamental transverse mode up to 30 [mW] can be obtained.
It was sufficient if ≦ 3 [μm] and Δη _eff ≧ 6 × 10 ⁻³ .

(Operation) With the above configuration, the layer embedded in the stripe-shaped groove (covering layer) is at least two layers of the high-refractive index layer and the low-refractive-index layer, so that the light exuding into the stripe-shaped groove can be made high. Due to the influence of the refractive index layer, an effective refractive index distribution that increases in the horizontal direction immediately below the stripe-shaped groove is generated on the bonding surface. Further, by optimizing the clad layer parameters, the current spreading in the active layer is sufficiently suppressed, and stable current confinement is possible in a wide optical output range over a high output operation near the oscillation threshold.

(Example) First, before describing an example, the basic principle of the present invention will be described.

Current spreading in a stripe laser as shown in Fig. 5 has already been studied (Japanese,
Journal, Of, Applied, Physics Magazine No. 12
No., 1585, 1973, and Journal of Applied, Physics, May 1978), can be expressed as follows. That is, the current density distribution J _y (y) outside the stripe is approximately J _y (y) = (I ₀ / l ₀ L) exp [− (| y | −S / 2) /
l ₂ ] ... Where L is the resonator length, S is the stripe width, and I ₀ is the spreading current. β is the junction parameter, q / nkT, ρs is the combined sheet resistivity, which is 1 / ρs = 1 / (ρ ₄ / d ₄ ) + 1 / (ρ depending on the resistivity and film thickness of each layer on the P side in the figure. ₃ / d ₃ ) ... Also, It is the total current value. l ₀ is
The width at which I ₀ is 1 / e of the maximum value indicates the spread width of the current in one direction and can be expressed as l ₀ = 2L / βρsI ₀ ....

Ρs from the equation, I _t, the relationship of l ₀ is, When I _t = I _th Here, J _th is the threshold current density.

The above results are based on an approximate analysis, and since the laser shown in FIG. 12 is different from the structure shown in FIG. 5, it is shown in FIG. 6 to analyze the current distribution of the laser shown in FIG. The simulation was performed using an equivalent circuit. The cross section of the laser was divided into meshes, divided into fine cells, and each cell was connected by a resistor, and a diode was arranged in the active layer portion. FIG. 7 is a simulation calculation example, showing the current dependence of the optical output P and the width ω of the current density distribution in the active layer. L ₀ and ρs obtained in this simulation
A plot of the relationship between and is a straight line with a slope of -1/2 with respect to the log-log plot as shown in FIG. 8, and it can be seen that the above approximate analysis is effective for the current spread width. On the other hand, the horizontal spread D of the guided mode in the laser of FIG. 12 is determined by the stripe width W and the effective refractive index difference Δη _eff in FIG. Assuming that the ratio of the spread width of the guided mode and the spread width of the current is η, η can be expressed as η = D / (S + 2l ₀ ).

As mentioned above, in order to obtain a laser in which the spot diameter does not change from low power at low threshold to high power operation,
It is necessary to make η a large value. According to the above simulations and actual device prototype experiments, if the ratio of the spread width of the guided mode to the spread width of the current is 50 [%] or more, that is, if η> 0.5, good current confinement is performed and the low threshold value is achieved. , It was found that a stable transverse mode with high differential efficiency can be obtained. Here, when the specific resistance of the P-clad layer is ρ ₂ and the film thickness is d ₂ , the conditions of ρ ₂ and d ₂ satisfying the equation are as follows: Becomes However, ρs = ρ ₂ / d ₂ and S = W + 2 (d ₂ −
The relationship of h) / tan θ was used.

On the other hand, regarding the N-side clad layer parameters, the value of the specific resistance was optimized by simulation using the equivalent circuit shown in FIG. FIG. 9 shows the calculation result. From this, it is understood that when the specific resistance of the N-clad is set to 0.1 [Ωcm] or less, the current constriction width ω becomes small, and at the same time, the threshold value can be lowered and the differential efficiency can be improved.

In order to qualitatively explain the effects described above, simulation examples of current distribution are shown in FIGS. 11 (a), (b) and (c). FIG. 11 (a) shows the resistivity of the P-cladding layer ρ ₂ = 0.06.
[Ωcm], film thickness d ₂ = 1.5 [μm], specific resistance of N-cladding layer ρ ₃ = 0.06 [Ωcm], and FIG. 2B shows ρ ₂ = 0.06 [Ωc
m], d ₂ = 1.5 [μm], ρ ₃ = 0.3 [Ωcm], same figure (c)
Is ρ ₂ = 0.2 [Ωcm], d ₂ = 1.5 [μm], ρ ₃ = 0.06 [Ω
cm] is substituted for the cladding layer parameter. The current spread becomes larger on the side where the specific resistance of the P and N cladding layers is relatively small. For example, FIG. 11 (a) (b) A comparison of (a) with respect to (b) is a large specific resistance [rho ₂ of N- cladding layer, thus the current would spread within P- cladding layer, the active The current spread in the layers is large. Further, comparing FIGS. 11 (a) and 11 (c), since the specific resistance ρ ₂ of the P-clad layer is larger than that of the N-clad layer, the current is
It can be seen that it spreads in the clad layer and does not spread much in the P-clad layer. Therefore, it is understood that making the specific resistance of the P-clad layer relatively large and the specific resistance of the N-clad layer small makes the current constriction effective. As for the film thickness of the P-clad layer, as is clear from the current distribution shown in FIG. 11, the smaller the film thickness d is, the more the spread of the current in the active layer can be reduced. By optimizing the current spreading in the active layer, the current spreading in the active layer can be suppressed sufficiently small, and a stable current confining effect can be provided over a wide optical output range from near the oscillation threshold to high output operation. Figure 10 (a)
(B) is a simulation example of the current dependence of the spread width of the optical output / current density distribution due to different cladding layer parameters. Fig. 10 (a) shows the case of unoptimized cladding layer parameters ρ ₂ = 0.4 [Ωcm], d ₂ = 1.5 [μ
m], h = 0.2 [μm], W = 2 [μm], θ = 45 °, β = 1
9, Jth = 1500 [A / cm ² ] and the left side of the formula is 2.7 [K
Ω], the right side is 4.9 [KΩ], and the formula is not satisfied.
In this example, ρ ₃ = 0.2 [Ωcm]. Note that this parameter is for a conventional laser. FIG. 10 (b) shows the case of the parameters determined so as to satisfy the formula, ρ ₂ = 0.1
[Ωcm], d ₂ = 0.3 [μm], h = 0.2 [μm], W = 2 [μ
m], θ = 45 °, the left side is 3.3 [KΩ], the right side is 1.2
It becomes [KΩ]. In addition, in FIG. 10 (b), ρ ₃ = 0.06
[Ωcm]. As is clear from the comparison of FIGS. 10 (a) and 10 (b), in FIG. 10 (b), the oscillation threshold is about 60 [%], the current spread width at the threshold is reduced by 70 [%], and the differential efficiency is also increased. ing.

With a laser having such a good current constriction effect, 1 [m
A stable spot diameter can be obtained in the vicinity of [W], and a transverse mode shape with little influence on both ends of the stripe can be obtained. Furthermore, since a hole burning phenomenon or the like due to a change in current distribution is unlikely to occur, a stable transverse mode can be obtained up to a high output.

Details of the present invention will be described below with reference to illustrated embodiments.

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention. In the figure, 11 is an N-GaAlAs substrate, 12
Is an N-Ga _0.6 Al _0.4 As clad layer, 13 is a Ga _0.92 Al _0.08 As active layer, 14 is a P-Ga _0.6 Al _0.4 As clad layer, and 15 is N-Ga.
_0.4 Al _0.6 As Current blocking layer (different layer), 16 is P-Ga _0.7 Al _0.3
As the first covering layer, 17 P-Ga _0.6 Al _0.4 As second coating layer, 18 denotes P-GaAs contact layer, 19 and 20 metal electrode layer, respectively.

The structured laser is realized by the steps shown in FIGS. First, as shown in FIG. 2 (a), an N-GaAlAs substrate 11 (Si-doped, 1 × 10 ¹⁸ c) having a plane orientation (100) is used.
1.5 [μm] thick N-GaAlAs cladding layer 12 on m ^-3 ).
(Se-doped, 6 × 10 ¹⁷ cm ^-3 ), undoped GaAlAs active layer 13 having a thickness of 0.06 [μm], P-GaAlAs cladding layer 14 (Zn-doped, 1 × 10 ¹⁸ cm ^-3 ) having a thickness of 0.3 [μm] ) And thickness 1 [μ
m] N-GaAlAs current blocking layer 15 (Se-doped, 5 × 10 ¹⁸ c
m ^-3 ), were grown in sequence.

The MOCVD method was used for this first crystal growth, the growth conditions were a substrate temperature of 75 [° C.], V / III = 20, a carrier gas (H ₂ ) flow rate of up to 10 [l / min], and the raw material was trimethylgallium. (TMG:
(CH) ₃ Ga), trimethyl aluminum (TMA: (CH ₃ ) ₃ A
l), arsine (AsH _3), P- dopant diethylzinc _{(DEZ: (C 2 H 5} ) 2 Zn), n- Dobanto in hydrogen selenide (H ₂ Se), growth rate 0.25 [μm / min ] It is not always necessary to use the MOCVD method for the first crystal growth, but crystal growth with a large area and good uniformity is possible.
The use of the MOCMD method is more advantageous than the LPE method when considering mass production.

Next, as shown in FIG. 2B, a photoresist 21 is applied on the current blocking layer 15, and a stripe-shaped window having a width of 2 [μm] is formed in the resist 21, and the current blocking layer 15 is formed using this as a mask. Selective etching was performed to form stripe-shaped grooves 22.

Then, after performing a surface cleaning treatment with the resist 21 removed, a second crystal growth was performed using the MOCVD method. That is, as shown in FIG. 2C, a P-GaAlAs first coating tank 16 having a thickness of 0.25 [μm] and a P-GaAl having a thickness of 1.25 [μm] are provided on the front surface.
An As second coating tank 17 and a P-GaAs contact layer 18 (Zn-doped, 5 × 10 ¹⁸ cm ⁻³ ) having a thickness of 5 μm were sequentially grown.
After that, the contact layer 18 is formed by a normal electrode attaching process.
The Cr-Au electrode 19 is on the upper surface, and the Au-Ge electrode is on the lower surface of the substrate 11.
20 was applied to obtain the structure shown in FIG. The sample thus obtained was cut into a Fabry-Perot type laser with a cavity length of 250 [μm] by cleavage, and the device characteristics were measured. The specific resistances of the N-clad layer 12 and the P-clad layer 14 of this device are 0.06 [Ωcm] and 0.1 [Ωc, respectively.
m].

FIG. 3 shows the current-light output characteristics and the spread width ω of the emission intensity distribution of the device manufactured by the above method.
In the figure, the white circles represent the half-width of the spread width, and the black circles represent the 1 / e ² width. Oscillation threshold is 25 [mA], slope efficiency is 0.31 [mW / mA]
Compared with FIG. 13, which is similar measurement data of the conventional example, the current spread during low current injection is reduced to less than half of FIG. 13, and a stable ω value is obtained from the threshold value. .
These characteristics correspond well with the results of the simulation shown in FIG.

Further, FIGS. 4A and 4B show near-field images of the laser having the characteristics shown in FIGS. 13 and 3. Even though they have the same stripe groove width, when the parameters of the cladding layer are not optimized and the current spread is large, the deformation of the mode which is considered to be the effect of both sides of the stripe as shown in FIG. 4 (a). Can be seen. In such a laser, mode instability occurs due to the hole burning phenomenon as the injection current increases. On the other hand, in the case of the laser of the example, a good shape was obtained as shown in FIG.

It should be noted that the present invention is not limited to the above-described embodiments, and the conditions satisfying the clad layer parameters that satisfy the above-described formula, and the dimensions and composition that the basic transverse mode can attain can be appropriately changed. The constituent material is not limited to GaAlAs, but other compound semiconductor materials such as InGaAlP and AlGaZnP may be used. Furthermore, as crystal growth, MO
It is also possible to use the MBE method instead of the CVD method. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, at least two layers, a high refractive index layer and a low refractive index layer, are embedded in the stripe-shaped groove portion to exude into the stripe-shaped groove portion. The generated light is affected by the high-refractive-index layer, and an effective refractive index distribution that increases in the portion directly below the stripe-shaped groove in the direction parallel to the bonding surface is generated. Therefore, an increase in excess threshold current can be suppressed, and a lower threshold value can be achieved. Furthermore, by optimizing the resistivity and film thickness of the cladding layer, the current spreading in the active layer is suppressed to a sufficiently small level, and stable current confinement is achieved over a wide optical output range over high output operation near the oscillation threshold. It is possible to have an effect, and in particular, it is possible to achieve a stable basic transverse mode from a low output near the threshold value to a high output operation of 30 [mW] or more.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention, FIGS. 2 (a) to 2 (c) are sectional views showing a manufacturing process of the laser of the above embodiment, and FIG. FIG. 4A and FIG. 4B are schematic diagrams showing near-field images of the conventional structure laser and the example laser, respectively, which are characteristic diagrams showing current-light output characteristics and current dependence of emission intensity distribution width ω in the example laser. 5 to 11 are each for explaining the outline of the present invention. FIG. 5 is a schematic diagram showing a laser structure used for the current spread analysis which has already been performed, and FIG. 6 is a conventional laser. 7 is a schematic diagram of an equivalent circuit used for the current distribution simulation of FIG. 7, FIG. 7 is a characteristic diagram showing the simulation result, and FIG. 8 is a result of the conventional current spreading analysis in which the current distribution simulation result shown in FIG. 6 is shown in FIG. Characteristic diagram showing that FIG. 9 is a characteristic diagram showing the dependence of the threshold current, the differential efficiency, and the current spread width on the N-clad resistivity value obtained by using the simulation of FIG. 6, and FIGS. FIG. 11 (a) to FIG. 11 (c) are schematic views showing a simulation example of a current distribution, and FIG. 12 shows a schematic structure of a conventional laser. A cross-sectional view and FIG. 13 are characteristic diagrams showing current-light output characteristics and current dependence of emission intensity distribution width ω in a conventional laser. 11 ... N-GaAs substrate, 12 ... N-Ga _0.6 Al _0.4 As clad layer,
13 ... Ga _0.92 Al _0.08 As active layer, 14 ... P-Ga _0.6 Al _0.4 As clad layer, 15 ... N-Ga _0.6 Al _0.4 As current blocking layer (different layer),
16 ... P-Ga _0.73 Al _0.27 As First coating layer, 17 ... P-Ga _0.6 Al
_0.4 As second coating layer, 18 ... P-GaAs contact layer, 19, 20 ...
Electrode, 21 ... Resist, 22 ... Striped groove.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-46584 (JP, A) JP 60-137085 (JP, A) JP 60-137083 (JP, A)

Claims (2)

[Claims] 1. A double-heterostructure portion made of a compound semiconductor material, which has a stripe shape different in conductivity type from the cladding layer on the side opposite to the substrate with respect to the active layer of the double-heterostructure portion. Forming a heterogeneous layer having a groove,
And in the heterojunction type semiconductor laser device in which a coating layer having the same conductivity type as that of the above-mentioned cladding layer is formed thereon to have a current constriction effect and a built-in waveguide effect, the heterogeneous layer is made of a compound semiconductor material containing Al. The coating layer is formed into at least two layers, and the first coating layer closer to the active layer is a layer having a refractive index higher than that of the cladding layer, and the first coating layer is closer to the active layer than the first coating layer. The distant second coating layer is a layer having a smaller refractive index than the first coating layer, and the specific resistance ρ ₂ of the clad layer on the side opposite to the substrate with respect to the active layer.
And the film thickness d _{2 of the} clad layer Where W: bottom width of stripe-shaped groove of different layer [cm] h: distance from active layer to first coating layer at bottom of stripe-shaped groove [cm] Δη _eff : effective refractive index difference between inside and outside of stripe-shaped groove D: stripe Of the waveguide mode in the direction parallel to the junction surface, which is determined by the bottom width W of the groove and the effective refractive index difference Δη _eff θ: Complementary angle of the angle between the bottom of the stripe groove and the side surface β: Current at the pn junction The diode characteristic parameter J _th when the voltage characteristic is expressed as I∝exp (βV _j ) is set so that the relation of threshold current density is satisfied, and the specific resistance ρ ₃ of the clad layer on the substrate side with respect to the active layer is set. A semiconductor laser device characterized by being set to 0.1 [Ωcm] or less. 2. The bottom width W of the stripe-shaped groove portion and the effective refractive index difference Δη _eff are set so that W ≦ 3 μm Δη _eff ≧ 6 × 10 ^−3. The semiconductor laser device described.