JPS6024084A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To multiply a longitudinal mode, and to settle the performance characteristics of low noises by bringing the thickness of an active layer in a laser element with a double hetero-junction type multilayer crystalline layer to 0.1mum or more and the thickness of a clad layer joining on the substrate side of the active layer to 0.2mum or more. CONSTITUTION:N-GaAs 2 is superposed on P-GaAs 1, and a V-shaped groove is formed and P-GaAs 3, a P-GaAs active layer 4, N-GaAlAs 5 and N-GaAs 6 are shaped in an epitaxial manner. A difference between mixed crystal ratios among the clad layers 3, 5 and the active layer 4 is brought to approximately 0.25-0.40 from carriers and an optical confinement effect. A boundary line between a multi-mode region M and a single mode region S is prescribed by the thickness d2, d1 of the active layer 4 and the clad layer 3 at that time. When d1 and d2 are changed, a high noise region Ef is prescribed while using a SN ratio -70dB as a boundary, and a region Ec having the short life of operation and a region Ed having long one are prescribed. Accordingly, when d1 and d2 are selected in accordance with a predetermined manner, a laser element, a longitudinal mode thereof is multiplied, is obtained, and the output characteristics of low noises applicable to a light source for a video disk can be settled.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to the structure of a semiconductor laser device, and more particularly to a semiconductor laser device having multiple longitudinal modes that are effective as signal light for disk devices and the like.

<Prior Art> Ever since semiconductor lasers have been used as signal beams for compact audio disc players, which are consumer products, the demand for semiconductor laser elements has increased rapidly. Semiconductor laser elements are small and lightweight, making them suitable as signal light sources for reading the information stored on the Dinuk board, but semiconductor lasers are used as signal light sources for video discs that read signals using a similar method. That is difficult. The main reason for this is that the noise of the semiconductor laser element is large, so that the image quality is greatly degraded compared to when a He--Ne laser is used, for example. In order to clearly reproduce video signals from video discs, it is necessary to use a light source with a very high S/N ratio. Therefore, it is necessary to use a semiconductor laser element, which has the characteristics of a compact light source, as a signal light source for video discs, etc. The S
The development of replacement systems to improve the /N ratio is being actively pursued.

<Objective of the Invention> The present invention provides a new and useful semiconductor laser device that has multiple longitudinal modes and established low-noise operating characteristics by making full use of technical means for the device structure of the semiconductor laser device, especially the crystal layer thickness. The purpose is to provide.

<Explanation of Embodiments> FIG. 1 shows a V-channel (V-channel) in which a V-shaped groove is formed on a substrate used as an embodiment of the present invention.
ledSubstrate Inner 5tripe
) 5 is a schematic cross-sectional view showing the basic configuration of a semiconductor laser device. An n-type GaAs current blocking layer 2 is formed on a p-type GaAs substrate 1.
After depositing.

By etching and forming nutripe-shaped 7-shaped grooves, a current path is opened from which the stain flow prevention layer 2 has been removed, and on top of this, p q , Ga As cladding layers 3 , p (or n) f
ipGaAs active layer 4, n-type GaA#As cladding layer 5
A double heterojunction type semiconductor laser device is constructed by sequentially epitaxially growing an n-type GaAs cap layer 6 and forming an n-side electrode 7 and an n-side electrode 8. When a current is injected through the n-side electrode 7 and the n-side electrode 8, the current flows through the active layer 4 using the 7-shaped groove as a current path.
Laser oscillation starts. Since the thickness of the n-type cladding layer 3 is thin outside the V-shaped groove, part of the light is absorbed by the substrate 1 in this part, and a refractive index difference is created, forming a waveguide mechanism. Further, the longitudinal mode is normally unified. When longitudinal modes are unified, the noise alone is small, but mode pop noise caused by temperature changes and noise caused by reflected light occur during mounting, resulting in a decrease in the S/N ratio. Incidentally, since the current path corresponding to the 7-shaped groove has an internal stripe structure with a very narrow width of 1 to 2 μm, it also has a gain waveguide effect, which has the effect of reducing noise. Furthermore, the internal stripe structure has a lower oscillation threshold current than the electrode stripe structure, and the far-field pattern is well-balanced.

In the semiconductor laser device having the above structure, the thickness of the n-type cladding layer 3 outside the V-shaped groove is di, and the thickness of the active layer 4 is dl.
The influence on the longitudinal mode when dl and dl are changed appropriately will be explained. By setting d1 + d2 in an appropriate range, the vertical mode can be multiplied, and the S/N can be sufficiently applied to the signal beam of the video digital device.
It has been found that a high output J laser beam can be obtained. FIG. 2 is an explanatory diagram showing a multimode mode region M defined by dl and dl, a single)v (single) mode region S, and their boundaries. The mixed crystal ratio of G a AIA s in the n-type cladding layer 3 and the n-type cladding layer 5 is both 0.4.
The mixed crystal ratio of the active layer was set to 0.14. The difference in the mixed crystal ratio between the cladding layers 3 and 5 and the active layer 4 is desirably set to about 0.25 to 0.40 in view of carrier and light confinement effects. As is clear from Figure 2, dl is 0.25 μ'
The longitudinal mode is multiplied when dl is 0.1 μm or more. In addition, if dl is 0, 'J21im or later'-, it will be multiplied even if d] is about 0.2ttm, and di
If dl is 0.35 μm or more, the multimode region M occurs even if dl is about 0.08 μm. The noise level measured when changing dl and dl was as shown in Fig. 3. In the figure, the Ea area is a low-noise area that can be sufficiently applied as a signal light source for a video disc, and the Eb area is a high-noise area that is unsuitable for a video disc. Further, the boundary corresponds to a level where the S/N ratio is -70 dB. Also in this figure, the conditions for dl and dl are approximately the same as the results in FIG. 2.

Note that the noise level was measured at a laser output of 3 mW.

When dl is set to 0.2511 m or more and dl is set to 0.1 μm or more, and the curve is plotted based on the curve, the result is as shown in FIG. The output was varied from 1 mW to il) 7 mW, and the Nubek l-/shi curves at each output intensity are shown.

The VSIS structure semiconductor laser device has a wide nuvector width (width of one longitudinal mode) of 1 to 2λ and poor coherence.
Noise caused by returned light is small. As is clear from the figure, in this semiconductor laser device, the longitudinal mode is noticeably multi-mode at an output intensity of 6 mW or less.

On the other hand, when dl and dl are set large, the oscillation threshold current becomes high, and the life of the device is shortened due to heat generation of the element. Fifth
The figure is a characteristic diagram showing the influence of changes in d, dl on the oscillation threshold current. The Ec region is a region where the oscillation threshold current is high and the operating life is short, and the Ed region is a region where the oscillation threshold current is small and the operating life is sufficiently long. The boundary line is when the oscillation threshold current is 9
Corresponds to a value of 0mA. As can be seen from the figure, under conditions where dl is smaller than 0.45 μm and dl is smaller than 0.2 μm, the oscillation threshold current is small and the operating life is long. When the oscillation threshold current becomes 90 mA or more, the actual operating current becomes 00 mA or more, and the life span is significantly reduced.

King tends to appear in the output vs. current characteristics at the cutting end, and the transverse mode becomes unstable: a new practical problem arises. Therefore, the upper limit of dl is 0.45 μm.

It is desirable to set the upper limit value of d2 to about 02μηL.

<Effects of the Invention> As explained in detail above, according to the present invention, a semiconductor laser element with multiple longitudinal modes can be obtained, and low-noise output characteristics can be established that can be applied as a light source for video disk devices, etc. can.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a VSIS type semiconductor laser device used as an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a multimode region and a single mode region defined by dl and d2. FIG. 3 is an explanatory diagram illustrating the noise level when changing dl and d2. FIG. 4 is a characteristic diagram showing output intensity and spectrum curve. FIG. 5 is a characteristic diagram showing changes in dl and d2 and their effects on the oscillation threshold current. 1... Substrate 2... Current blocking layer 3... P-type cladding layer 4 - Active layer 5... N-type cladding layer 6...
Cap layer agent Patent attorney Aihiko Fukushi (and 2 others) Q OJ
q2 03 04 Q5 01; 07 011--1-→-dtOtmFig.5

Claims (1)

[Claims] 1. In a semiconductor laser device having a double heterojunction multilayer crystal layer stacked on a substrate via a nutripe-like current path, the active layer thickness of the multilayer crystal layer is 0.1 μm.
Above, the cladding layer bonded to the active layer on the substrate side was 0.2μ
7. A semiconductor laser device characterized in that each of the semiconductor laser elements is set to 7 m or more.