JPH02178989A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce an oscillation threshold current and an astigmatic difference and to decrease noises by forming a ridge region in a 2-stage structure consisting of a ridge and a current injection path formed on the ridge, and making the width of the ridge larger than that of the current injection path. CONSTITUTION:A ridge region is formed in a 2-stage structure having a ridge 12 and a current injection path 13 formed on the ridge 12, and the width W1 of the ridge 12 is larger than the width W2 of the current injection path 13. Thus, since the ridge 12 having a second clad layer 7 of the thickness adapted for a self-excited oscillation is excited near the gain region of an active layer 5, the distribution of the light generated from the current injection path 13 is suitably extended. Since the width W1 of the ridge 12 is larger than the width W2 of the current injection path 13, the distribution of the light can be made larger than the width of the active layer 5 to which a current is injected. Since the thickness of the second clad layer 7 is thin outside the ridge 12, an equivalent refractive index difference between the inside and the outside of the ridge 12 is increased. Thus, an oscillation threshold current, an astigmatic difference can be reduced, and noises can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device having low noise characteristics.

(Prior Art) Semiconductor lasers used in fields such as video disc players are required to have extremely low noise. Semiconductor laser devices that utilize self-sustained oscillation phenomena are often used to meet such demands for low noise characteristics. By utilizing the automatic oscillation phenomenon, a single oscillation spectrum becomes multi-longitudinal mode I. Furthermore, the spectral width of each longitudinal mode is widened, resulting in low noise characteristics. Several proposals regarding such automatic oscillation semiconductor laser devices have been made (for example, Rinji 2 IEICE Technical Report MW84-24.P, 65 (1984),
2 Suzuki et al., IEICE Technical Report 0QE8 as having a slightly different structure.
4-57. P, 39 (1984)).

FIG. 4 shows an example of a conventional self-oscillation semiconductor laser device. This semiconductor laser element has VSIS (Vchannel
ed 5ubstrate Inner 5tripe
) has a structure. n-GaA on p-GaAs substrate 41
An s-current blocking layer 42 is formed, and a V-shaped groove 50 reaching the substrate 41 from its surface is formed. Above that p-A
lGaAs cladding layer 43. A] GaAS active layer 44.
n-AlGaAs cladding layer 45゜n, -Ga A
An s-gap layer 46 is formed by epitaxial growth, and an n-side electrode 47. A P-side electrode 48 is provided. The self-sustained oscillation phenomenon is caused by increasing the layer thickness d of the cladding layer 43 on both sides of the V-shaped groove 50 for current confinement (thus weakening the refractive index waveguide mechanism and enlarging the two light emitting spots).

However, in such a semiconductor laser device, since the distribution of light becomes large, the absorption of light by the active layer 44 and the current blocking layer 42 becomes large in areas other than the region where gain can be obtained. Therefore, there is a drawback that the oscillation dark value current becomes large. The oscillation dark value current of the semiconductor laser device shown in FIG. 4 is about 50 mA, which is a large value. Furthermore, this semiconductor laser has a disadvantage in that the one-stigmatism difference is large because the refractive index waveguide mechanism is weak.

(Problems to be Solved by the Invention) In order to reduce the oscillation dark value current, it is possible to form the active layer into a quantum well structure. The quantum well structure is usually M B
E (Molecular Beam! Epitax
y) method or M OCV D (Metalorgani
c Chemical Vapor Deposjti
on) method. However, the semiconductor laser device shown in FIG. 4 is grown by a liquid phase epitaxy method, which makes it possible to obtain a V-shaped groove 50'' and a flat active layer. The controllability of the thickness is poor, and the controllability of a thin quantum well structure of about 100
Good reproducibility (the term rotation is formed).Furthermore, according to the MBE method or the MOCVD method, it is not possible to obtain a flat active layer in the V-shaped groove 5O-).

In order to avoid this problem, it is conceivable to form the current confinement structure after forming the quantum well structure. An example is not shown in Figure 3. An n-GaAs buffer layer 22.n-AI is formed on the n-(1; a As substrate 2) by the MBE method.
C; aAs cladding layer 23. AlGaAs gradient index light guide layer 24. AlGaAs multiple quantum well active layer 25
．． AlGaAs graded refractive index light guide layer 26. p-AI
GaA, scrat layer 27. p-GaAs scan 1 layer 2
Form 8 continuously. The Al mixed crystal ratio of the gradient refractive index type light guide layers 24 and 26 gradually decreases from the side farther from the active layer to the side closer to the active layer. Next, a striped current injection path 32 (width W3 - about 2.5 μm) is formed using a first lithography and active ion beam etching method, and a SiNx break-through film 29 is formed. After that, p
A side electrode 30 and an n-side electrode 31 are provided.

Even in such a semiconductor laser device, since the layer thickness d of the p-cladding layer 27 on both sides of the current injection path 32 is large, the area where the current injection path 32 exists and the existence of the current injection path 32 on both sides thereof are large. The difference in equipolarized refractive index between the regions without and without is small. Therefore, low noise characteristics due to automatic oscillation can be obtained.

Since the active layer has a quantum well structure and there is no current blocking layer, absorption of laser light is small and the oscillation dark value current can be reduced. However, in this semiconductor laser element, like the semiconductor laser element shown in FIG. 4, the refractive index waveguide mechanism is weak, so the characteristics of the laser light are still close to those of the laser light due to the gain waveguide mechanism. Therefore, the astigmatism difference is extremely large, and is larger than that of the beam.

In view of the above problems, two objects of the present invention are to provide a semiconductor laser device having low oscillation dark value current, small astigmatism difference, and low noise characteristics.

(Means for Solving the Problems) A semiconductor laser device of the present invention was formed on a semiconductor substrate. A laminated structure having a first ground layer, an active layer, and a second cladding layer, and a ridge region formed above the laminated structure, the ridge region being formed at the ridge portion and the ridge portion. The width W of the ridge portion is larger than the width W2 of the current injection path, thereby achieving the above object.

Also, the thickness dl of the second cladding layer in the ridge portion, and the distance from the interface of the active layer on the second cladding layer side to the surface of the second cladding layer outside the ridge portion. Thickness d. 0.3μm≦d, o+d+≦1.0μm0.1μm≦d
It is also possible to set o≦0.5 μn+.

Furthermore, the width W of the ridge portion and the width W2 of the current injection path can be set to 3 μm≦W1≦8 μm, 0.5 μm≦W2≦4 μm.

(Function) In the semiconductor laser device of the present invention, since there is a ridge portion having a second cladding layer with a thickness suitable for automatic oscillation near the gain region of the active layer, current is not injected from the current injection path. The distribution of the generated Rage 1 light spreads appropriately. Furthermore, since the width of the ridge portion is larger than the width of the current injection path, the distribution of light can be made larger than the width of the active layer where two currents are injected, resulting in an automatic oscillation state. Since the thickness of the second crat layer is thin outside the ridge, the difference in equilateral refractive index between the inside and outside of the ridge becomes large.

Therefore, the refractive index waveguide mechanism is strengthened and the astigmatism difference is reduced.

Also, the thickness d of the second cladding layer inside the ridge portion and outside the current injection path. ld, 0.3μm≦
do4−d+≦] and Q71m, automatic oscillation is effectively caused.

and the thickness d of the second crand layer outside the ridge.
By setting l to o and 1 μm≦do≦0.5 μm, the refractive index waveguide mechanism can be strengthened and the astigmatism difference can be reduced. .

Further, by setting the width W of the ridge portion and the width W2 of the current injection path to 3 μm≦WI≦81tm O, and 5 μm≦W2≦41tm, a configuration more suitable for self-assisted oscillation can be achieved.

(Example) The invention will now be described with reference to examples.

FIG. 1 is a cross section V showing an embodiment of the semiconductor laser device of the present invention. An n-GaAs buffer layer 2 (thickness 1 μm) and an n-Al
GaAs cladding layer 3 (thickness 12 μm), AlGaA
s-gradient refractive index type light guide layer 4 (thickness 0.2 μm), A
lGaAs single quantum well active layer 5 (thickness 70 nm), A
lGaAs gradient refractive index type light guide layer 6 (thickness 0.2 μm
), pAIGaAsAlGaAs cladding layer 7 μm) p
- A GaAs cap layer 8 (thickness: 0.511 m) was continuously formed. The A1 mixed crystal ratios of the gradient index light guide layers 4 and 6 gradually decrease from those farther from the active layer 5 to those closer to the active layer 5. Next, the width W is
, =4.5 .mu.m, and then etching was performed to a depth of 25 .mu.m by reactive ion beam etching. This etching forms a ring-shaped portion with a width W of 4.5 μM. Next, using the photolithography method again, the above width W = 4.5 μm was glued to the center of the Fuji shape part with a width W2-
After forming a 2 μm striped resist mask,
By reactive ion beam etching method, the depth d
2=1.4 μm etching was performed. By the above-described two etching steps, the ridge portion 12 and the ridge-shaped current injection path 13 are formed. The ridge portion 12 has a height d, =02
5 μm2width W = 4.5 μm. The ridge-shaped current injection path 13 has a height d2=1.4 μm and a width W2−2 μm. and the thickness d from the top surface of the active layer 5 to the surface of the cladding layer 7 outside the ridge portion 12 . is a light guide layer 6 inside the current injection path 13; When the total thickness of the cladding layer 7 and the cap layer 8 is D, it is given by do --D (d+ +dz). Since D is 1.9 μm, the thickness is d.

−〇, it becomes a 25μ river. Thereafter, an SiNx insulating film 9 is formed on the entire surface using the plasma CVD method, and an S
The iNχ insulating film 9 was removed. Next, the substrate 1 was polished to a wafer thickness of about 100 μm, and then an n-side electrode 10 and an n-side electrode 11 were formed. This was divided into chips with a resonator of 300 μm using the interfold method to obtain semiconductor laser devices.

In this embodiment, the width W of the ridge portion 12 is -4.5μ.
Since m is larger than the width W2-2 μm of the current injection path 13, automatic oscillation can occur.

Also, the thickness d of the optical guide layer 6 and the cladding layer 7 inside the ridge portion 12 and outside the current injection path 13. +d
, = 0.5μ, the difference in equivalent refractive index between the inside and outside of the current inlet path 13 is small, and has a size suitable for automatic oscillation.

Thickness d from the negative surface of the active layer 5 to the surface of the crat layer 7 on the outside of the ridge portion 12. -0.25 μm, the difference in equivalent refractive index between the inside and outside of the current injection path 13 becomes large. Therefore, the refractive index waveguide mechanism is strengthened,
The astigmatism difference is small.

The astigmatism difference of the semiconductor laser device of this example was 10 μm or less, which was a small value. Also, the oscillation dark value current is 15~
The value was as low as 20 mA.

In this embodiment, the optical guide layer 6 and the crat layer 7 on the inside of the ridge portion 12 and on the outside of the current injection path 13 are
Thickness d. -1-d, is 0.3 μm to 1.0 μm
m was suitable. Light guide l”N on the outside of the ridge
G and the thickness d of the crat layer 7.

A suitable thickness was 0.1 μm to 0.5 μm.

A suitable width W1 of the ridge portion 12 was 3 to 8 μm, and a suitable width of the current injection path 13 was 0.511 m to 4 μm.

FIG. 2 shows a second embodiment of the semiconductor laser device of the present invention. n-GaAs substrate 1'' second n-G by MBE method
a A s buffer layer 2. n-AlGaAs cladding layer 3. AlGaAs light guide layer 14 (thickness 0.2μ
m), AlGaAs multiple quantum well active layer 15 (well layer...thickness 70 people 1 layer number 3. Barrier layer...thickness 35 people 2 layers number 2), A, IC; aA, s light guide layer 16 (thickness: 0.2 μm), p-AlGaAs cladding layer 7 (thickness: 1, 2 μm), p-GaAs cap layer 8 (thickness: 0.2 μm).
5 μm) was continuously formed. In this embodiment, unlike the embodiment shown in FIG. 1, the active layer 15 has a multiple quantum well structure, and the optical guide layers 14 and 16 have a uniform composition. Next, a resist mask was formed using a photolithography method in a striped region having a width W of 5° and 5 μm and in regions on both sides of the region where the groove 17 was to be formed. Next, by reactive ion beam etching, etching was performed to a depth of dl-0.3 μm to form a ridge-shaped portion having a width of 9 W1. Using the photolithography method again, a resist mask is formed in the striped region with a width W2-3 μm at the center of the ridge shape portion with the width W and in the regions on both outer sides of the groove 17, and then a reactive ion beam is applied. By the etching method, the depth dz = 1. , 4 am etching was performed. By the above-described two etching steps, the ridge portion 12 and the ridge-shaped current injection path 13 are formed. The height of the ridge part 12 is d, = [ ] 3μM2 width 3μm5
．． It has a 5 μm ridge shape.

The current injection path I3 has a height of 2 dz = 1. 4 μm,
It becomes a ridge shape of W2-3 μm. Thickness d of the light guide layer 16 and the ground layer 7 outside the ridge portion 12.

= 0.2 μm, and the outside of the ridge portion 12 forms a mesh of the light guide layer 16. Furthermore, after forming the SiN χ insulating film 9 in the region excluding the upper flat surface of the current injection path 13, the P-side electrode 10. And an n-side electrode 11 was formed.

In this embodiment, since the ridge portion 12 and the current injection path 3 are formed by forming the groove 17, it is possible to form a shape that leaves the area outside the groove 17 on the growth side opposite to the substrate 1 side. It becomes possible to use the surface as a mounting surface. By mounting in this manner, heat dissipation characteristics are improved, and output characteristics and reliability are improved. When the semiconductor laser device of this example was mounted on the growth side, the oscillation dark value current was 15 to 20 mA, and the astigmatism difference was 10 μm or less.

(Effects of the Invention) The semiconductor laser device of the present invention has a small oscillation dark value current5 as described above, low noise through automatic oscillation, and a reduced astigmatism difference, so it can be used as a light source for video disc players, etc. It is most suitable as

In addition, the semiconductor laser device of the present invention has excellent layer thickness controllability.
Since it can be manufactured by BE method or MOCVD method, it is possible to manufacture an element that causes automatic oscillation at a high yield.

Figure 1 is a cross-sectional view of the first embodiment of the semiconductor laser device of the present invention, Figure 2 is a cross-sectional view of the second embodiment of the present invention, and Figure 3 is a cross-sectional view of the second embodiment of the present invention. FIG. 4 is a sectional view showing an improved example of a conventional self-oscillation semiconductor laser device.

1.2], -n-GaAs substrate, 3.23-nA]
GaAs ground layer, 4,6,24.26-A]G
aAs graded refractive index optical guide layer, 5... single quantum well active layer, 7.2l-=p-AIGaAs cladding layer, 8
．． 28... p-GaAs core layer 12... ridge portion, 1.3.32... current injection path, 1416... optical guide layer, 15... multiple quantum well active layer 17... groove .

”−

Claims (1)

[Claims] 1. A laminated structure formed on a semiconductor substrate and having a first cladding layer, an active layer, and a second cladding layer, and a ridge region formed above the laminated structure. , a semiconductor laser device in which the ridge region has a two-stage structure including a ridge portion and a current injection path formed on the ridge portion, and a width W_1 of the ridge portion is larger than a width W_2 of the current injection path.