JPS59172287A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser element, the increase of noises therefrom is prevented and coupling efficiency thereof with an optical system is improved, by providing an index waveguide mechanism and a self-oscillation phenomenon. CONSTITUTION:A Te doped n-GaAs current stopping layer 2 is grown on a Zn doped p-GaAs substrate 1, a groove 7 reaching to the p-GaAs substrate 1 in a striped shape from the current stopping layer 2 is formed, and a Zn doped p- Ga0.5Al0.5As p type clad layer 3, an undoped Ga0.95Al0.05As active layer 4, a Te doped n-Ga0.8Al0.2As intermediate layer 10, a Te doped n-Ga0.7Al0.3As n type clad layer 5 and a Te doped n-GaAs cap layer 6 are deposited on the groove in succession. An Au-Zn p side electrode 8 is formed to the GaAs substrate 1 and an Au-Ge-Ni-Au n side electrode 9 to the cap layer 6, thus manufacturing a semiconductor laser element in resonance length of 250mum and width of 300mum. The refractive indices n1, n2, n3, n4 of each layer of the p type clad layer 3, the active layer 4, the intermediate layer 10 and the n type clad layer 5 are set in order of n2>n3>n4>n1.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a semiconductor laser device that reduces interference noise caused by returned light.

<Prior art> Conventionally, when a semiconductor laser device is used as a light source for a disk device, when coupled with the optical system of a video disk or an audio disk, the return light of the output laser beam due to reflection from the disk surface is transmitted to the semiconductor laser element. As a result, the linearity between the injected current and the optical output decreases as shown by the solid line in FIG. 1 due to the interference of the re-incoming light with the output light, and the linearity between the injected current and the optical output is reduced as shown by the solid line 71 in FIG. As shown, the noise of the output light may increase, making it impossible to put it into practical use. As a means to solve this problem, the current injection width of the semiconductor laser, that is, the stripe width is increased from the usual 10 to 15
Carrier diffusion length in the active layer compared to μm, that is, 2 to 4
Attempts have been made to narrow the width to about μm to avoid distortion or increase in return optical noise. In such a semiconductor laser, the optical distribution of the laser is determined by the gain distribution, but since the cavity volume is small, spontaneous emission light has a large contribution to the laser mode, and the injection current density is large, so the gain spectrum is The width is expanded, oscillation occurs in a multi-axis mode, and the influence of re-incident light is reduced by this multi-axis mode oscillation. Furthermore, carriers injected into the active layer diffuse in the lateral direction, causing carrier oscillation between the laser oscillation region and the non-laser region. As a result of causing the oscillation phenomenon, the output laser light is FM modulated by AM modulation and a change in the refractive index in response to the increase and decrease of carriers, and the oscillation spectrum width is expanded to about IX. This shortens the coherent length of the laser beam and makes the phase of the light reflected from the optical system and re-injected into the laser element disordered, eliminating interference noise with the re-incoming light and eliminating the interference of the re-incoming light. Impact is reduced.

However, semiconductor laser elements with a gain waveguide mechanism have unstable coupling with the optical system due to changes in the near-field image due to injection current or changes over time, and large astigmatism, which makes it difficult to connect with optical systems such as lenses. If the coupling efficiency decreases, there will be further drawbacks.

Therefore, when it is necessary to consider the stability of the output laser beam and the coupling between the laser beam and the optical system, a waveguide type semiconductor laser element with a refractive index of 1 is required.

As an example of a conventional index-guided semiconductor laser device, FIG. 3 shows a V-channel semiconductor laser device having an internal current confinement structure. A current blocking layer 2 made of 1l-GaAs for restricting the current path is formed on the p-GaAs substrate 1.
- p-type cladding layer 3 made of GaAlAs, p or n-
Active layer 4 made of GaAlAs (or GaAE!)
, n n-type cladding layer 5 made of GaAlA3, n-
A cap layer 6 made of GaAs is successively deposited by liquid phase epitaxial growth. A on the GaAs substrate 1
The p-side electrode 8 is made of u-Zn, and the cap layer 6 is made of Au.
An n-side electrode 9 made of -G e -N 1-Au is formed by vapor deposition. Since the region where the current blocking layer 2 is interposed is bonded with opposite polarity, no current flows, and only the striped groove portion 7 from which the current blocking layer 2 is removed serves as a current path. In addition, the p-type rad layer 3 in the groove portion 7 and other parts
Utilizing the difference in the layer thickness, a difference is created in the projection of the laser light generated in the active layer 4 to the substrate l, and an effective refractive index difference is created between the oscillation region and the non-oscillation region. Reflecting the fact that this semiconductor laser element is of the refractive index waveguide type, stable oscillation states can be obtained in both near-field and far-field patterns, and there is no astigmatism. It has the characteristic of high coupling efficiency with the optical system because it has almost no aberrations.However, when the return light of the output laser beam re-enters this semiconductor laser element, as explained in Figs. 1 and 2, The problem of interference noise arises due to the return light.

This is because, in the conventional V-channel semiconductor laser device as shown in FIG. 3, the internal current confinement structure is close to the active layer, and the reactive current (current that does not contribute to oscillation) flowing into the non-oscillation region is extremely small. Because the self-oscillation phenomenon seen in narrow stripe lasers does not occur, and the effective refractive index difference between the oscillation region and the non-oscillation region due to light seepage is relatively large, carriers as described below This is because the temporal vibration component of the effective refractive index difference based on the vibration of This is a new and useful semiconductor that fundamentally solves the above-mentioned drawbacks, and has a refractive index waveguide mechanism and imparts a self-oscillation phenomenon, thereby preventing an increase in noise and improving the coupling efficiency with the optical system. The purpose of this invention is to provide a laser device.

In general, the effective refractive index difference (
In a refractive index guided semiconductor laser device provided with a refractive index (ΔN), the ΔN is determined in response to the amount of "seepage".An intermediate layer having a refractive index smaller than that of the active layer is provided adjacent to the active layer. By inserting the active layer, it is possible to change the laser beam electric field intensity distribution in the stacking direction with the active layer as the center, and to control ΔN in response to changes in the amount of "1" seeping into the substrate. On the other hand, as mentioned above, in the active layer, the injected carriers oscillate temporally due to carrier consumption accompanying oscillation and lateral diffusion of carriers, and in response to this, the oscillation region and non-oscillation region are separated. The refractive index difference between is a temporally oscillating component (
Zn). In a normal index-guided semiconductor laser device, no vibration effect is observed because Zn is sufficiently small compared to ΔN. By decreasing ΔN, a self-oscillation phenomenon will appear even in the index-guided semiconductor laser device, and the spectral width of the uniaxial mode will be expanded. This is a technique that attempts to suppress the increase in return optical noise in a semiconductor laser device by utilizing the effect.

<Example> FIGS. 4(A) and 4(B) are a cross-sectional configuration diagram and a refractive index distribution diagram of a groove section XX section of a semiconductor laser device showing an example of the present invention.

In this example, the active layer is This method reduces the amount of generated laser light that "seeps into the substrate" and easily causes the aforementioned self-oscillation phenomenon.Hereinafter, using a GaAs-GaAlAs semiconductor laser as an example, FIG. 4(A) The element structure shown in FIG.

Zn with a carrier concentration of +
5XI018 was deposited on a doped p-GaAs substrate by liquid phase epitaxial growth in order to limit the current path.
Te doped n-G with carrier concentration of cm-s
a) After growing the As current blocking layer 2 to a thickness of 08 μm, grooves 7 are etched in a stripe pattern from the current blocking layer 2 until reaching the p-GaAs substrate 1. ○The width of the striped groove 7 is 31 trn. On top of this, Znn-doped-GaO05A was grown again by liquid phase epitaxial growth.
], 0,5 A 3 p-type rat layer (refractive index H) 8 layer thickness (outside the groove) 0.2 μm 1 undoped GaO
, 95A10. Active layer made of Q5AS (refractive index n2)
4 to 0, I μm, Tedodon-Gao, gA
lo, 2 Intermediate layer consisting of As (refractive index na) I
O'31'mz Tedodon-Ga0.7Alo
, 3 an n-type cladding layer (refractive index n4) 5 made of As and a cap layer 6 made of 1 μm XTe-doped n-GaAs.
are sequentially deposited to a thickness of 3 μm. The GaAs substrate l has Au-
The p-side electrode 8 made of Zn and the cap layer 6 are made of Au-Ge.
-Ni-Au n-side electrode 9 is formed by vapor deposition. Next, the resonance length is 250 μm depending on the bone.

A semiconductor laser element with a width of 300 μm is used.

p-type cladding layer 3. Active layer 4. Middle layer 10. The refractive index of each layer of the n-type cladding layer 5 is nl, n2. n3 and n4 are set to <n2>na>n4>nl as shown in FIG. 4(B).

A current is injected into the active layer 4 using the striped grooves 7 as current paths, and laser oscillation is started from the active layer 4 directly above the grooves 7. The p-type cladding layer 3 is thick in the groove part 7 and thin in other parts than the groove part 7, so that an effective refractive index difference is formed in the lateral direction as in FIG. That is, a refractive index waveguide type semiconductor laser element is constructed which basically utilizes the difference in the amount of laser light generated in the active layer 4 that permeates in the direction of the substrate 1.

FIG. 5 shows the current-optical output characteristics and oscillation spectrum characteristics of a conventional index-guided semiconductor laser (dashed line) and an index-guided semiconductor laser equipped with the intermediate layer IO according to the above embodiment (solid line). .

In the semiconductor laser according to the above embodiment, since the intermediate layer 10 having a smaller refractive index than the active layer 4 is provided adjacent to the active layer 4 on the opposite side to the substrate 1, the light in the stacking direction within the active layer 4 is The confinement factor is lowered and the amount of light seeping into the substrate I is reduced.

Due to the reduction in the light seepage effect, the lateral light confinement within the active layer 4 is also weakened, which increases the oscillation threshold compared to conventional semiconductor lasers, but the difference between the lasing region and non-oscillating region also weakens. An effect appears in which the effective refractive index difference ΔN between the two oscillates over time, and the uniaxial oscillation spectrum width expands.

In Fig. 5, this uniaxial oscillation spectrum width is o, o
O] It is shown that it has expanded from about X to about IX. By manufacturing a laser element in which the refractive index n3 of the intermediate layer IO is appropriately changed, the amount of light "seepage" is changed, and the effective refraction between the laser oscillation region and the non-laser region in the active layer 4 is changed. When the index difference ΔN is controlled, the uniaxial mode spectrum width of the output laser beam caused by the self-oscillation phenomenon is appropriately expanded and controlled. Therefore, both the near-field image and the far-field image of the output laser beam can be stably maintained.

In the above embodiments, a GaAs-GaAlAs semiconductor laser device was explained, but it goes without saying that the present invention can also be applied to semiconductor laser devices made of other materials. Furthermore, the values of the layer thickness and composition of each layer used in the above examples do not limit the scope of application of the present invention.

<Effects of the Invention> As explained in detail above, according to the present invention, the uniaxial mode spectrum width of the output laser beam is expanded, and interference noise caused by return light due to reflection from an irradiated object such as a disk surface is suppressed. Ru. In addition, there is little change in the near-field image and far-field image,
Good coupling efficiency with the optical system can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the injection current versus light output characteristic of a conventional semiconductor laser device. The solid line is the characteristic curve when there is re-incident light, and the broken line is the characteristic curve when there is no re-incident light. FIG. 2 is a diagram showing the noise characteristics of a conventional semiconductor laser and device. The curve L1 is a characteristic curve when there is re-incident light, and the curve t2 is a characteristic curve when there is no re-incident light. FIG. 3 is a cross-sectional view of a conventional refractive index waveguide type semiconductor laser device. FIGS. 4(A) and 4(B) are a cross-sectional configuration diagram of a semiconductor laser device and a refractive index distribution diagram of a groove section XX, showing an embodiment of the present invention. FIG. 5 is an explanatory diagram showing the injection current versus optical output characteristics and oscillation spectrum characteristics of the conventional semiconductor laser device and the semiconductor laser device shown in FIG. DESCRIPTION OF SYMBOLS 1... GaAs substrate, 2... Current blocking layer, 3...
p-type cladding layer, 4... active layer, 5... n-type cladding layer, 6... cap layer, IO... intermediate layer agent
Patent attorney Aihiko Fukushi (and 2 others) Posted by XVL Mitsuru 11th 10h Written by: Ll-, 601'C No. 2 Illustration (A)
(B))λ 4Fyl

Claims (1)

[Claims] 1. Forming striped grooves for current confinement on a substrate and depositing a multilayer crystal having an active layer for laser oscillation, and leaking light from the active layer toward the substrate in a non-oscillation region. In a semiconductor laser device in which a refractive index waveguide mechanism is formed, an intermediate layer having a refractive index smaller than that of the active layer is inserted adjacent to an interface of the active layer in a direction opposite to the substrate; A semiconductor laser device characterized in that the amount of light leakage is controlled. 2. The semiconductor laser device according to claim 1, wherein the multilayer crystal is made of a GaAlAs-based compound semiconductor material.