JPS63202986A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device with small astigmatism and excellent noise characteristics, by setting the length of a current blocking layer in the direction of a resonator as the length wherein loss exceeds gain and laser oscillation does not occur, said current blocking layer being arranged outside a groove perpendicular to the direction of the cavity. CONSTITUTION:A P-type GaAs semiconductor substrate 1 is provided with a groove 9. In the groove 9, an N-type AlxGa1-xAs current blocking layer 9a is formed, on which a P-type AlyGa1-yAs lower clad layer 10a is arranged. Outside the groove 9, an N-type AlxGa1-xAs current blocking layer 9b is formed, on which a P-type AlyGa1-yAs lower clad layer 10b is arranged. As the clad layer 10b is thinner than the clad layer 10b, a light oozing out of an AlzGa1-zAs active layer 5 is liable to be absorbed by the outer part of the groove 9 on the P-type GaAs semiconductor substrate 1 and the N-type AlxGa1-xAs current blocking layer 9b. Therefore, by increasing the light absorption amount of this part, the effective reflectivity distribution in the transversal direction is intensified, and the laser light confinement efficiency is increased. Thereby, astigmatism can be reduced without losing excellent noise characteristics.

Description

[Detailed Description of the Invention] [Industrial Application Field] The invention of B relates to a semiconductor laser device with reduced astigmatism.

[Conventional technology]

FIG. 2 is a perspective view showing the structure of a conventional semiconductor laser device.

In this figure, 1 is a p-type GaAs semiconductor substrate, which is doped with an acceptor such as Zn at a high concentration. 2ban type A I X G 1Ll-X A, s
This current blocking layer is epitaxially grown on a p-type GaA, s semiconductor substrate 1 and doped with a donor such as Te. 3 is a groove for current confinement, which is an n-type A4XGa
, -XAsT5 flow blotter block layer 2 is processed and formed into a live shape, and p-type GaAs semiconductor substrate 1 is exposed. 4 is a p-type A lyGa, yA s lower cladding layer, and an n-type A j XG a, -XA S current blocking layer 2
P-type GaAs is layered on top of the groove 3 for current confinement.
It is electrically connected to the semiconductor substrate 1. 5 is AI
, Gal-.

As active layer, 6 is n-type A I rGa, -rAs lower cladding layer, p-type A e yGa, -yAs lower cladding layer 4. Together with the Al□Ga knee and the As active layer 5, it constitutes a double heterojunction. 7 is the n-type AA,
G al-, As n laminated on the upstream layer 6
The type GaAs cap layers 8a and 8b are electrodes that are in A-mic contact with the n-type GaAs cap layer 7 and the p-type GaAs semiconductor substrate 1, respectively, and are made of, for example, AuGe, Ni,
The main material is Au.

Next, let me explain how it works.

No forward voltage is applied between the electrodes 8a and 8b.
j! zG a, -, As active layer 5 a PNt8
: When this happens, a forward electric field is generated and a current flows. At this time,
The current flows only through the current confinement groove 3 due to the depletion layer generated between the n-type A U, Gal-, As current blocking layer 2 and the p-type ApyGa, □As lower cladding layer 4.

Then, local lateral current confinement and current injection into the A n 2G a, 2A, S active layer 5 occur. Also,
p-type A RyG al-yAs lower cladding layer 4. A
, p2G tLx-zAs active layer5. n-type A n
Since current confinement in the junction direction occurs due to the tuple/telojunction formed with the rG al-rAs lower cladding layer 6, light emission occurs due to efficient carrier recombination. Furthermore, the p-type AlyGal-yAs lower cladding layer'LpA, nzGIL1zAs
Active layer 5. Since light is confined in the junction direction due to the refractive index distribution of the n-type Al, Gal-rA, s lower cladding layer 6, stimulated emission of light is performed efficiently.

In addition, in the groove 3 portion for current confinement, Ai is used.

Part of the light seeping out from the Gat-zAs active layer 5 is n-type A.
The lateral complex refractive index distribution generated by absorption in the n XG al-xA s current blocking layer 2 confines light in the lateral direction, resulting in stable laser oscillation in the lateral mode. and p-type AIyGa, -yA
By setting the thickness of the s lower cladding layer 4 to an appropriate value, the absorption amount of the AStS current blocking layer 2 to the n-type Al' value and l/, A I zG &+-
By guiding the mechanism of recombination and stimulated emission within the zAs active layer 5 to self-oscillation and increasing the oscillation spectrum linewidth, we can obtain a laser operation that is less susceptible to the influence of returned light and has less noise. can.

[Problem that the invention seeks to solve]

In order to increase the oscillation spectrum linewidth and reduce noise, the conventional semiconductor laser device described above is
lJj Al x Gal - 5 In order to have the effect of reducing noise, n-type A, 1-G a 1
□The amount of light absorbed by the As current blocking layer 2 cannot be increased to a constant value. Therefore, the horizontal refractive index distribution cannot be strengthened, and the position of the vertical and horizontal focal points of the laser beam cannot be increased. There was a problem in that the deviation, that is, the astigmatism was large.

The present invention was made to solve these problems, and an object of the present invention is to provide a semiconductor laser device that can reduce astigmatism without losing good low-noise characteristics.

[Means for solving problems]

The semiconductor laser device according to the present invention has a first groove in which a groove perpendicular to the cavity direction is formed except for the vicinity of the end face in the cavity direction.
a conductive type semiconductor substrate; formed on the semiconductor substrate;
A current blocking layer of a second conductivity type having a groove for current confinement in the direction of the resonator, and a first conductivity type having a flat surface formed on the current blocking layer and on the semiconductor substrate in the groove portion for current confinement. a lower cladding layer of B, an active layer sequentially formed on the lower cladding layer of B, and an upper cladding layer of a second conductivity type;
The thickness of the lower cladding layer in the groove perpendicular to the resonator direction is set to be sufficient to generate a self-oscillation effect and expand the spectral line width. The length of the resonator of the current blocking layer in the groove perpendicular to the resonator direction is made long enough for the gain to exceed the loss and cause laser oscillation, and one of the current blocking layers outside the groove perpendicular to the resonator direction is The length in the resonator direction is such that loss exceeds gain and laser oscillation does not occur.

[Effect]

In this invention, the current blocking layer in the groove perpendicular to the resonator direction only produces absorption for producing self-oscillation, and the current blocking layer outside the groove perpendicular to the resonator direction absorbs the laser beam horizontally. Produces absorption for directional confinement.

〔Example〕

FIG. 1 is a perspective view showing the structure of an embodiment of a semiconductor laser device of the present invention.

In this figure, the same symbols as in Fig. 2 indicate the same parts,
A groove 9 is formed on the p-type GaAs semiconductor substrate 1 by, for example, wet etching, orthogonal to the resonator direction. 9a is the n-type A l x G al- in the groove 9;
xA s current blocking layer 9b is the n-type A1. The Ga knee and As current blocking layers are each grown to a uniform thickness by, for example, MO-CVD.

10a is p-type A I yG al-, A in the groove 9;
s lower cladding layer 10b is the p-type Al outside the groove 9.
The yG Al□As lower crack lower layer and the lower Rudd layer are each grown by, for example, a liquid phase epitaxial growth method, and the surfaces are flattened by optimizing the growth conditions.

In addition, the p-type AlyGal-yAs lower cladding layer 10a in the groove 9 formed in the p-type GaAs semiconductor substrate 1
The thickness of the n-type A I
l, and the p-type A e yG al-yA outside the groove 9
When the thickness of the s lower cladding layer 10b and the length of the n-type AlxGa1-XAS current blocking layer 9b on the outside of the groove 9 in the cavity direction are respectively j2+12, t□jt
The relationship between 2#JIP12 is t I> t 2. tl 1
>> In addition to being 211x, the thickness is t when operating the semiconductor laser device.

A value of 11 is thick enough to cause self-oscillation and expand the spectral linewidth, a value of 11 is long enough for gain to exceed loss and cause laser oscillation, and a value of 4□ However, the loss exceeds the gain, and the length is such that laser oscillation is not possible.

Next, its operation will be explained.

In the semiconductor laser device of the invention of B, if a forward voltage is applied between the electrodes 8a and 8b as in the conventional semiconductor laser device, laser light with a wide spectral linewidth and low noise characteristics can be obtained using the same principle. However, in this invention, p-type Ga
A groove 9 is provided in the As semiconductor substrate 1, and n in the groove 9 is
p on type AIX Gat-xAsAs current blocking layer 9a
Type A lyG 111-yA S lower cladding layer 10a
Compared to the film thickness of the n-type A l xG a, - outside the groove 9,
p-type A 1 yG a on xAs current blocking layer 9b,
□Since the film thickness of the As lower cladding layer 10b is thinner, A
The light leaking from the active N5 is transmitted to the outer part of the groove 9 of the p-type GaAs semiconductor substrate 1 and the n-type A I XG a, -XA s current blocking layer 9b.
easily absorbed.

Therefore, by increasing the amount of light absorbed in the portion B, the effective refractive index distribution in the lateral direction becomes stronger, the confinement efficiency of the laser light increases, and the astigmatism becomes smaller.

On the other hand, the film thickness of the p-type Al yGa, -yAs lower cladding layer 10a on the n-type Al, GIL, -XAS current blocking layer 9a in the groove 9 is the same as that of the conventional semiconductor laser device. Therefore, the wide spectral linewidth and the resulting low noise characteristics are not impaired.

In the above embodiments, the conductivity type of the semiconductor substrate is p-type, but the present invention is not limited to this, and the present invention uses a semiconductor substrate of the opposite conductivity type, that is, n-type, and changes the conductivity type of each semiconductor layer. Similar effects can be obtained even if the conductivity types are opposite to each other.

Further, in the above embodiment, a semiconductor laser device using GaAs thread material was described, but the same applies to other 1[-V group compound semiconductor laser devices.

〔Effect of the invention〕

As explained above, the present invention includes a semiconductor substrate of a first conductivity type in which a groove perpendicular to the resonator direction (]0) is formed except in the vicinity of the end face in the resonator direction; a second conductivity type current blocking layer having a current confinement groove in the direction of the current confinement; and a first conductivity type current blocking layer having a flat surface formed on the current blocking layer and on the semiconductor substrate in the current confinement groove portion It consists of a lower cladding layer, an active layer sequentially formed on the lower cladding layer, an upper cladding layer of the second conductivity type, and a cap layer of the second conductivity type, and is formed in the groove perpendicular to the resonator direction. The thickness of the lower cladding layer is set to be sufficient to generate self-oscillation effect and expand the spectral linewidth, and the length of the resonator of the current blocking layer in the groove perpendicular to the resonator direction is set so that the gain and loss are reduced. In addition, the length of the current blocking layer on the outside of the groove perpendicular to the resonator direction was set to a length that would not cause laser oscillation because the loss would exceed the gain. This has the advantage that the lateral refractive index distribution can be strengthened at the end facets, and a semiconductor laser device with small astigmatism and good noise characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of an embodiment of a semiconductor laser device of the present invention, and FIG. 2 is a perspective view showing the structure of an example of a conventional semiconductor laser device. In this figure, 1 is a p-type GaAs semiconductor substrate, 3 is a groove for current confinement, 5 is A4□Ga am-, As active layer,
6-ban type Al rG al-rAs lower cladding layer,
7 type GaAs chip layer, 8a, 8b electrode, 9
is a groove, 9a and 9b are n-type Al zG &, -XAL
s current blocking layer, 10a, 10b1. ip type A e
yGa, -yA s lower cladding layer. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A semiconductor substrate of a first conductivity type in which a groove orthogonal to the resonator direction is formed except for the vicinity of the end face in the resonator direction; a second conductivity type current blocking layer having a groove; a first conductivity type lower cladding layer formed on the current blocking layer and on the semiconductor substrate in the current confinement groove portion and having a flat surface; The lower cladding layer is composed of an active layer formed in sequence on the lower cladding layer, an upper cladding layer of a second conductivity type, and a cap layer of the second conductivity type. The thickness is set to be sufficient to generate self-oscillation effect and expand the spectral linewidth, and the length of the resonator of the current blocking layer in the groove perpendicular to the resonator direction is set so that the gain exceeds the loss and the laser In addition to having a length sufficient to cause oscillation, the length in the direction of one of the resonators of the current blocking layer outside the groove perpendicular to the direction of the resonator is set to such a length that loss exceeds gain and does not cause laser oscillation. Semiconductor laser device. (2) The thickness of the lower cladding layer in the groove perpendicular to the resonator direction and the length of the current blocking layer in the groove in the resonator direction are respectively t_1 and l_1, and the thickness of the lower cladding layer outside the groove Claim 1 is characterized in that, where the length of the current blocking layer outside the groove and the length of one of the current blocking layers in the resonator direction are respectively t_2 and l_2, t_1>t_2 and l_1>>2l_2. ) The semiconductor laser device described in item 2.