JPS63142879A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To inhibit return-beam noises, to emit laser beams having small astigmatic difference and to enable low threshold current oscillation, in which reactive currents flowing on the outside of an active region are suppressed extremely, by making the width of an optical guide narrower than a central section in the vicinity of at least one resonator end surface and forming a buried layer by a II-VI compound semiconductor. CONSTITUTION:A II-VI compound semiconductor ZnSe buried layer 208 is shaped through an MOCVD method. A shaded part represents a II-VI compound semiconductor layer and a stripe at a central section a section in which a P-type GaAs contact layer 206 is exposed through etching. The width of an index waveguide and current injection width are brought to the same extent in the vicinity of resonator end-surfaces and an index waveguide mechanism is shaped, thus allowing stable single transverse mode oscillation, then emitting laser beams having extremely small astigmatic difference. On the other hand, the width of said index waveguide is made sufficiently wider than current injection width at the central section of a resonator and a gain waveguide mechanism is formed, thus allowing longitudinal multiaxis mode oscillation, then exceedingly inhibiting return-beam noises.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a semiconductor device with low noise and stable compensation mode characteristics.

[Conventional technology]

When a semiconductor laser (hereinafter referred to as LD) is used as a light source for an optical information processing device, etc., there is noise (hereinafter referred to as return optical noise) generated when a part of the emitted light returns to the resonator due to reflection. ) may occur, making it impossible to use for disaster relief. As a means to reduce this return + noise, the reflectance of the end face is increased by compensating the I and Tl resonator end faces with multiple layers of G1 bodies with different refractive indexes; etc. As an example of the latter, Japanese Patent Application Laid-Open No. 60-140,774. JP-A-60-15068
There are 2.

On the other hand, the commonly used liquid layer growth method (
(hereinafter referred to as the LPK method), a method for forming the entire top-V group compound semiconductor layer, or an organometallic vapor phase bottom length method (hereinafter referred to as the M
There is a method of forming an entire m-v group compound semiconductor layer by selective growth (referred to as OCvD method). An example of the latter is the Japanese Journal of Applied Physics (ffapanese).
ofApplia Physics) Vol. 25 No. 6 L498-I, 500 pages 1986.

[Problem that the invention seeks to solve]

However, the prior art described above has the following problems.

In the method of stacking #4 bodies with different refractive indexes in multiple layers on the end face of the LD resonator to increase the end face reflectance and reduce the influence of the return source and reduce the return optical noise, the film of each dielectric layer is stacked to increase the reflectance. It is necessary to accurately control the wavelength of the emitted light of the ykLD. In addition, the high reflectance at the end face reduces the intensity of the emitted light. Therefore, when a high output is required, such as when writing information onto a disk, it is necessary to further increase the LD drive current. An increase in the LD drive current increases power consumption, raises the O temperature inside the element, and reduces the reliability of the element.
This reduces the lifetime by one layer, and also increases the LD fabrication process of laminating more than one film.Next, in the method of reducing longitudinal multi-axis mode oscillation and return optical noise, a double heterojunction structure ( DH groove structure will be described below.) After formation, a gain waveguide type L is formed by forming electrode stripes on the upper surface.
It is possible to use Di.

The gain waveguide type LD is capable of vertical multi-axis mode oscillation, and the influence of noise caused by returned light and the like is reduced. However, in the gain waveguide type -D, the laser excavation light in the direction parallel to the junction is guided within S''a due to the gain distribution formed by the injected current. The surface is not flat and has wavefront aberration, that is, astigmatism occurs, and a complicated optical system is required to focus the light on a minute spot.Furthermore, the near-field image changes due to fluctuations in the injected current or returned light. The coupling with the optical system is unstable9, which poses a problem when applied to various devices.

An embodiment devised in consideration of the above problems (Japanese Patent Application Laid-Open No.
150682)'i shown in FIG. Figure 5 Yu > e (c)
vc shows a cross-sectional view of this element. The shape of the groove formed under the active layer (505) is different between the central part of the resonator and the vicinity of the end face. As shown in FIG. 3(c), the current blocking layer (301)K
By forming a recess that is wider than the width of the fi flow injection groove, the refractive index waveguide width becomes optically wider than the current injection width, and as a result, a gain waveguide mechanism is formed in the center of the element, and a longitudinal multiaxial mode is generated. Oscillation is obtained. This results in an LD having a refractive index waveguide width near the resonator end face and a gain waveguide mechanism at the center. However, in order to realize this purchase, a complicated process of forming grooves of different depths after forming the current blocking layer (301) is required, and since each layer is formed by the LPE method, it is difficult to control the film thickness. I have a sexual problem. Variations in the groove shape due to the formation of a complex-shaped substrate and variations in the film thickness of each growth layer lead to variations in the characteristics of the LD element.<s Lp
In the x method, since the growth rate of each layer in the groove portion and the flat portion differs greatly, it is difficult to control the film thickness, and variations in characteristics become a major problem.

Furthermore, a ridge-shaped waveguide for DH fabrication by stacking IV compound semiconductor layers is fabricated using the above-mentioned T, PI method or MOC! In the case of an LD'''C buried with an IV group compound semiconductor layer formed by the VD method, the influence of reactive current flowing outside the active region cannot be ignored.The present invention therefore solves this problem. The purpose of this is to perform stable single-transverse mode oscillation from low optical output operation to high optical output operation, suppress return optical noise by vertical multi-axis mode oscillation, and generate a single-mode laser with small astigmatism difference. Emit laser light and suppress reactive current flowing outside the active region as much as possible7
The purpose of this invention is to provide a semiconductor laser that oscillates with a low threshold current.

[Means for solving problems]

Semiconductor 1 of the present invention A semiconductor 1/1 comprising a ridge-shaped original waveguide 7M made of a nose U, I-1' group compound semiconductor, and a buried layer made of a semiconductor layer on the side surface of the optical waveguide.
- In the case, the width of the core waveguide is narrower in the vicinity of at least one resonator end face than in the center, and the buried nozzle is M
-Features characterized in that the semiconductor layer is made of a VE group compound semiconductor.According to the mg of the present invention, one nose oscillation source is guided by the gain waveguide groove in the central part of the resonator. Because of this, vertical multi-axis mode oscillation with less return light noise is performed, and since the laser oscillation light is guided by a refractive index waveguide mechanism near the output end face, stable single-transverse mode oscillation with less astigmatism difference is possible. 1) Since the structure is embedded with a high-resistance I-2 compound semiconductor, the reactive current is extremely small, resulting in a semiconductor I/-Z that oscillates at a low threshold voltage.

〔Example〕

The present invention will be explained in detail below.Here, AjlGa, which is a representative of the IV group compound semiconductor, is used as the part constituting the lip.
Although As-based semiconductors are used, the same applies to other compound semiconductors.

(Example 1) One example of the present invention will be described as the first factor. Figure 1(a)
1 shows a sectional view near the end face of the resonator, and FIG. 1(1)) shows a sectional view at the center. FIG. 2 shows a process for achieving the structure of an embodiment of the present invention, and the present invention will be described below with reference to FIG.

n-type GaAs substrate (201), n-type GaAs buffer layer (202), n-type A 11 x Gat-cAs first cladding layer (203), AAyGa 1-yAs active 111 (X>7) (204), p-type AftzGa+
-2A8 second cladding layer (z>y) (2os), pi
A DI trench structure consisting of a GaAs contact layer is continuously formed. (FIG. 2(a)) For the formation of each of the above layers, LPKi
-% by any method such as MOOVD@ or uMBK method
It is possible. A resist mask (207) for etching is then formed using a normal photolithography process. (FIG. 2(b)) The shape of the resist mask (207) is as shown by diagonal lines in FIG. 2(C). followed by 1
p-type GaAs contact layer (206) and p-type A as a mask for etching
Etching a portion of the AzGa+-zAs second cladding layer (205) followed by K+/resist mask 207
) to remove. (Second Capacity (d)) Next, an I-M group compound semiconductor Zn5e buried layer (20B) is formed by the MOOVD method. (Figure 2 (θ)) Other i- other than ZnSe
It is also possible to use w-group compound semiconductors. Subsequently, photolithography process and ZnEIθ buried layer (209)
Perform the etching process. A top view of the element after etching is shown in FIG. 2(b). The shaded area is the part where the pWGaAs contact layer (206) is exposed by etching in the central stripe of the l-M group compound semiconductor. Thereafter, a p-side electrode (210) is formed, a backside substrate cutting process is performed, and an n-side electrode (211) is then formed to form a semiconductor 1 node of the present invention.

AJ of any hft mixed crystal ratio in the refractive index of the Zn5e buried layer (209) used in the present invention! This value is smaller than that of the GaAs layer, and the forbidden band width is AJ of any A2 mixed crystal ratio.
It is a wider material than the AGaAs layer. Therefore, in a waveguide that is formed in an uninventive manner, since the laser oscillation light is not absorbed by the Zn5e layer, a refractive index difference formed by the real part of the complex refractive index occurs in the direction horizontal to the junction, and the refractive index guide It becomes a wave path.

In addition, the residue after etching of the second cladding layer is an important parameter that determines the refractive index difference in the direction horizontal to the junction.
The film thickness is AA()aAa because the refractive index of the Zn5a layer is small.
Even if the thickness is made thicker than in the case of a buried layer, a refractive index difference that enables single-compensation mode oscillation can be obtained.

In the vicinity of the resonator end face, the width of the refractive index waveguide and the current injection width are approximately the same, creating a refractive index waveguide mechanism, which enables stable single-transverse mode oscillation and emits laser light with an extremely small astigmatism difference. be done.

On the other hand, in the center of the resonator, by making the width of the refractive index waveguide wider than the current injection width, it becomes a gain waveguide groove, which causes vertical multi-axis mode oscillation, and returns optical noise can be suppressed as much as possible.

Furthermore, since the ZnBe layer is a material with a higher resistivity than the AIGaA layer, current confinement is effectively performed and reactive current flowing outside the active region can be suppressed as much as possible.

(Embodiment 2) FIG. 4 is a structural diagram showing another embodiment of the present invention. Fourth
FIG. 4(a) is a cross-sectional view near the end face of the resonator, and FIG. 4(b) is a cross-sectional view at the center of the resonator.

This example has a structure in which, in the formation of the rib waveguide in the above-mentioned (Example 1), the etching proceeds to the GaAs substrate side under the active layer (402) and after t, it is buried with a Zn5e buried layer C401).

The reasons why the vertical multi-axis mode oscillation and stable t-single-transverse mode oscillation and the astigmatism difference are extremely small, as well as the reason why the reactive current is extremely small, are the same as in the section (Example 1).

〔Effect of the invention〕

As described above, according to the present invention, the following effects can be obtained.

1) In the center of the resonator, light is guided by the gain waveguide horizontal groove, so the LD of the present invention oscillates in a longitudinal multi-axis mode. Therefore, the return optical noise becomes an extremely small value.

2) Due to reasons 1), it can be widely applied to light sources for information processing, etc. 3) At least near one of the resonator end faces, the light waveguide is performed by a refractive index waveguide mechanism, so normal refraction is not possible. Similar to the index waveguide type LD, the LD of the present invention also provides stable single-transverse mode oscillation even when the injection current changes.

4) For the same reason as 5), laser excavation light with extremely small astigmatism difference can be obtained.

5) 1) 3) 4) For the following reasons, when the LD of the present invention is incorporated into an optical head or the like, a complicated optical system required for output beam shaping etc. is not required. Therefore, simplification and weight reduction are concerned.

&) Since the current confinement layer is formed of an l-■ group compound semiconductor that provides a layer with high resistivity, it is possible to suppress as much as possible the reactive current flowing outside the active region. Therefore, it is effective to reduce the threshold current.

7) Since the present invention has excellent uniformity and reproducibility over a large area in film quality and film thickness, and can be produced by two-step growth using the MOOVD method, the LD of the present invention can be tabulated. Its characteristics are also excellent in uniformity, reproducibility, and reliability.

8) As mentioned above, I and D of the present invention are LDs with low noise, excellent transverse mode stability, and small astigmatism difference.

Therefore, by forming a protective film on the resonator end face of the LD of the present invention to prevent end face deterioration, high output characteristics can be obtained in addition to the above characteristics.

9) Since the refractive index of the embedded I-VI group compound semiconductor is small, the spot size of the near-field image can be controlled by changing the thickness of the remaining upper cladding layer.
Effective for increasing output.

10) Although the high-frequency 'ML quantity method is currently considered effective for reducing noise, the LD of the present invention can achieve lower noise without requiring such an additional method. Therefore, it is possible to achieve smaller size, lighter weight, and lower value without requiring additional circuits.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are sectional views showing an embodiment of T and D of the present invention. FIG. 2(a) to (a) are the ninth manufacturing process diagrams for realizing the entire LD of the present invention. FIGS. 5(a) to 5(0) are diagrams showing conventional examples. FIGS. 4(a) to 4(b) are sectional views showing one embodiment of the LD of the present invention. 201---nfiGaAs substrate 202...n type GaAs buffer layer 203=・n
Type AJ! xGa +-xAs first cladding layer 204, --.ARyGa 1-yAs active layer 205,
,, p-type ARzGa 1-zAs second cladding layer 20
6...p-type GaAs contact layer 207, 208...
・1nodist mask 209 for etching...Zn8s
Buried layer 210...P-side electrode 211...N-side electrode 301...Current blocking)-502...Active layer AOl...ZnEle Buried layer 402...Active layer 31 elements

Claims (1)

[Claims] In a semiconductor laser comprising a ridge-shaped optical waveguide made of a heterojunction structure of III-V compound semiconductor layers, and a buried layer made of a semiconductor layer on the side surface of the optical waveguide, the vicinity of at least one cavity end face is provided. Then, the optical waveguide is buried with a II-VI group compound semiconductor layer and the width of the optical waveguide is made almost equal to the current injection width to form a refractive index waveguide. 1. A semiconductor laser characterized in that an optical waveguide is embedded and the width of the optical waveguide is made sufficiently wider than the current injection width to serve as a gain waveguide.