JPS5812389A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser whereof the threshold current is low, the whole of the active region is buried with a matter having a small refractive index, and the device has the characteristic to perform extremely stable fundamental mode oscillation, and at the same time, the device is enabled to be manufactured having favorable reproducibility easily by one time liquid phase growth. CONSTITUTION:An SiO2 film 11 is adhered on the (100) face of an InP insulating substrate 10doped with Fe, an opening is formed as to be formed perpendicularly to the (01-1) face, and the half of the SiO2 film is removed. Then the SiO2 film 11 is removed, a P type InP clad layer 12 is made to grow as to have thickness along the A face to 0.5mum, and then an undoped InGaAsP active layer (lambda=1.3mum)13 is made to grow as to have thickness along the A face to 0.2mum. Then liquid phase growth is performed continuously as to bury the whole with an N type Inp clad layer 14, and as to make the upper part of the upper row part of stair to have 2mum thickness, and the respective layers are made to grow at the same time. When the wafer is put in a vacuum quartz ampoule together with a diffusion source Cd2P3 and is heated, Cd is diffused up to 2.4mum depth, and the diffusion front 16 reaches in the P type InP clad layer 12 (Cd diffusion region 17). Then a P type electrode 18 and an N type electrode 19 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser.
Long-wavelength semiconductor lasers using crystal materials such as InGaAsP are attracting attention as light sources with low transmission loss in optical fibers, and their practical use is progressing. In order to meet these requirements, a semiconductor laser that exhibits stable fast-transverse mode oscillation over a wide range of operating currents, suppresses slow floating oscillations, and exhibits excellent dynamic characteristics is required for practical use. A striped structure for each building was proposed and prototyped.

Among them, Hirai et al. published the Journal of Applied Physics (Journal of Appli
ed Physics) Magazine Volume 51 4539 Negative ~ 45
Reported on page 40 &N le InP/InGaAsP
B H semiconductor laser is made of InGaAsP in the active region.
It has a structure in which a (λ-L 3 μm) layer is surrounded by InP which has a low refractive index and serves as a cladding layer, and a current injection region is provided in a part of the cladding region in contact with the active value range. @
Since the BH semiconductor laser has a cladding layer not only in the vertical direction of the active region but also in the horizontal direction, it has a rectangular refractive index distribution based on the refractive index difference and maintains stable transverse mode oscillation fr. The active region and the flow confinement region coincide, and excellent characteristics can be expected, such as a small current and suppressed relaxation oscillations. However, if the active region remains embedded in the cladding layer, current leaks from the cladding layer adjacent to the active region, which serves as the injecting region, to the cladding 1- adjacent to both ends of the cladding layer.・＼The current was not effectively injected, the threshold current increased, and the concealment percentage was poor (6). To overcome this drawback, a Φ cladding layer having the same electrical characteristics as the current injection region with respect to leakage current is usually used as a blocking layer at both ends of the active region. However, the block layer becomes thicker and '11tflIL
When it comes into contact with the cladding layer serving as the injection region, current flows from the injection protection region to the block layer having the same electrical characteristics, and the leakage current increases rapidly.

On the other hand, when the block layer was thin, the current flowed over the block layer, and there were no blocking young fruits. Therefore, in order to effectively control the programming process, it is necessary to grow the block layer to the same thickness as the active region and to match both ends of the active region, and it is extremely difficult to control this growth.
Therefore, it was impossible to make it with good quality. Furthermore, in the case of BH semicircular bodies, fundamental transverse mode oscillation occurs, so it is necessary to create an active region with a width of 21 mm or less, and to facilitate the growth of block layers, buried cladding layers, etc. However, it is necessary to control the depth and shape of the etching, so it is necessary to control the etching depth and shape.

For this J'L, the one-shot method is relatively easy and can be formed by one liquid phase growth. 6 B H half 41 + racer 1
I nGaAs P/I nP terraced safstrait (TerraccHd 5ubs) with the following structure
trate (T S ) semiconductor laser was developed by Moriaki et al.
of Applied Physics), Volume 19, pages 2191-2196. The above-mentioned TS April laser has an n-InP base formed in a step-like manner.
1nP95y layer, InGaAs)' active layer, p-In
This was created by adding P cladding and continuously adding Haniji.

At this time, in liquid phase growth, i! Since the lateral growth rate in the step shape is P, the layer thickness of the In(JaAsP active layer formed along the step shape is thicker than that in the flat part, and the active layer of the above T8 semiconductor laser is Since the current continues along the stairs to the flat areas above and below, the current is not necessarily concentrated at the oscillation head and is ineffective. The threshold value is 1 compared to the BH semiconductor laser.
The current is more than doubled.

The purpose of the present invention is not only to eliminate the above-mentioned drawbacks and completely block both reactive current and leakage current to reduce the threshold current, but also to trap the entire active region with a material with a small refractive index, thereby reducing the extremely feminine fundamental transverse mode. The object of the present invention is to provide a 1,4-body laser that has excellent properties such as excavation, and at the same time has a structure that can be easily manufactured with good reproducibility by one-time liquid phase growth.

The semiconductor leopard of the present invention consists of at least a first conductive type first cladding 1--an active l---second conductive type@2 cladding 1m on an insulating substrate having a step-like surface. It has a three-layer structure, and the surfaces of at least the first cladding 1- and the active layer maintain a step-like shape, and the first conductive layer is formed in a flat region with a step-like step force). An impurity-introduced region indicating a mold was formed from the surface of the second cladding layer to a depth reaching the first cladding layer, and an electrode was formed on the surface of the second cladding layer corresponding to the surface of this impurity-introduced region and above the stepped portion. It has a structure.

Such a structure can be easily realized by utilizing the difference in crystal growth luck υ due to plane orientation. Example E will be described below, in which the ■-■ family member is used as an insulating substrate.

On the (100) surface of the Kawa-V group insulating substrate, (011
) When a staircase is formed with the A(111) plane as the hypotenuse so as to be perpendicular to the A(111) plane, it becomes the A(111) plane.
The plane and the (111) plane have an angle of 54 and 44 with respect to the (100) plane. When liquid phase growth is performed in this structure, A11
iil is a growth rate of about 3 compared to a flat (100) plane.
(because it's twice as fast)! ! While the first cladding layer and active layer grow steadily in the direction of the A plane, the growth rate on the flat (100) plane, which is the upper step F of the staircase, is slow and the growth layer thickness is extremely thin. It is also a matter of not letting it grow.

When growing from the 1,000 m part to the A side, the active no is thin, so the growth l- tends to be interrupted at the edge part. If the active layer grows and embeds a second layer with a second layer, the active I- grown along the A plane will become a foil surrounded by the cutulad j-, forming the BH chihiro body laser. It has a structure similar to . Especially 1nGaAsP/lnP long wavelength wavelength body 4
In the case of laser beams, the InP insulating substrate becomes the cladding layer.
Pi structure can be easily formed.

Historically, in six previous designs, impurities of the same conductivity type as the cladding layer of the agl were diffused into the lth cladding layer to provide a current pressure inlet, and between the first cladding layer and the second talarad l- Apply a voltage / ) structure. Therefore, in this structure, 1. LiI
Unlike the ``1'S'' P conductor laser in E, the injection current is injected into the active layer that momentarily contacts the M layer from the 1st Hood layer force, and is injected into the active layer by 16 μm. 1 can be ignored.In the flat part of the history, since it is adjacent to the insulating base, there is no <M f-1μ();・ from the active 1-,
In addition, since the active layer in the flat area and the layer thickness of the first layer and layer are extremely thin, the resistance increases in the horizontal direction. The reactive current is also extremely small, and these synergistic results)
Compared to body lasers, lasers below the henchmen can only oscillate at a threshold value.

The above-mentioned superimposed structure does not only use the Hyorin 1 Dojo board, but is also different from the conventional structure.It is necessary to limit the current injection area and reduce the ineffective I4L flow.

On the other hand, with the conventional T8+4 construction, it was difficult to achieve first-class control, and the reduction of the threshold current was rare due to the inability to reduce the threshold current. Moreover, according to the present invention, a 691-t structure can also be manufactured using liquid phase growth, for example, InP.
Taking an insulating substrate as an example, if Br methanol is used as the etching agent, the A-plane orientation can be easily obtained and the reproducibility can be improved.
ft step-like shape is formed, growth is easy, active layer thickness can be freely controlled, and reproducibility is high.

The active region of the semiconductor laser formed according to the present invention is surrounded by a cladding layer as described above, and is made of, for example, InGa.
In the case of AsP/InP semiconductor lasers, the growth thickness of the active region is 0.2 to 0.4 μm, and the length in the lateral direction parallel to the (100) plane is 2 μm to 3 μm or less21. If this is the case, stable fundamental transverse mode oscillation can be maintained. Furthermore, in the conventional T8 structure, not only the stepped portions (some flat portions also tended to emit light), but in the structure according to the present invention, only the active region oscillates, and there is no light stain in both the horizontal and vertical directions within the surrounding cladding layer region. It becomes a concentric point light source, which increases the coupling efficiency with the original fiber.

That is, the present invention has the following young fruits.

(2) Since the semiconductor laser according to the present invention can effectively inject current into the active region, it can oscillate at a low threshold value with less reactive current and leakage current.

■It can be formed by one-time liquid phase growth on an insulating substrate formed in a step-like manner, and has unparalleled excellent reproducibility.0■
Since the entire active region is surrounded by a cladding layer, refractive index guiding is dominant, and extremely stable fundamental transverse mode oscillation can be maintained over a wide current line range. ■The light source can be placed close to the equicentric sun and the coupling efficiency with the fiber can be increased.

An embodiment of the present invention will be described below with reference to the drawings.

One SiOz film 11 is applied on the (H-river) plane of the Fe-doped 1nP insulating substrate 10, a window is opened using a photoresist method so as to be perpendicular to the (011) plane, and half of the S-mount 2 film is smeared off. Next, by etching using 13r methanol solution #111, a step with the A side as a slope is formed (FIG. 1). At this time, the depth between the upper stage of l'i* stage and stage F is 1μ.
Rub ml.

Next, add 5i02i11 and add p-InP layer 1.
2/: I so that the thickness along the -A plane is 0.5 μm
After a while, the undoped 1N (JaAsP active layer (λ=x, aμm) 13 was grown to a thickness of 6.2 mm along the A plane.
/J In to grow. In this case, the growth rate in the A-plane direction is about three times faster than that on the flat (100) plane, so the growth rate on the flat (100) plane is (0.2 μmO, respectively).
p-InP% 0.07 μm InGaAsP L 7
0zJ & costume IJ.

Moreover, the part of the 6 upper ridge that grows from the flat part to the (111) A plane is cut off by the constriction. So p
- The length of the InP cladding layer 12 in the direction parallel to the (100) plane is 1.08 μm.
The length in the direction parallel to the oo) plane is approximately 0.8 μm.

Next, liquid phase growth is continuously performed so that the entire layer is buried with the n-1nP cladding layer 14 so that the top part of the stairs has a thickness of 2 .mu.m, and each layer is yellowed at a glance (FIG. 2).

Next, a window is opened using a temporary photoresist method in which a 5i02 film 15 is formed on the growth surface so as to include the upper step of the stairs and the vicinity of the edge of the 91fi+ plane. Next, the wafer is placed in a vacuum quartz sample chamber with a diffusion source CdgPa and heated at 565°C for 4 hours. Cd is diffused to a depth of 2.4 μm, and the diffusion front 16 reaches the p-InP cladding layer 12.
Diffusion region 17). AuZn was deposited on the Cd diffused surface43
Zero-order In(
8102 of the part located above the jaAsP active area 13
A window is opened in the film 15 using a photoresist method, and AU-Me Ni is vapor deposited and alloyed at 350° C. to form an n-type film 19.

In this situation, the Cd diffusion region and the n-In outside it are
A voltage is applied between the P cladding layers, but the section is short, approximately 2 μm in depth, and has a large bandgap.
Because of the n association, the 'kL flow is effectively introduced into the active region from the p-InP cladding layer.

Although the improvement article has been described with respect to 1nP/InLjaAsP, it can also be applied to other materials such as JaAs/AI GaAs.

1 is a cross-sectional view of a semicircular laser obtained by

In the figure, 10... InP insulating substrate, 11...
...8i0-membrane.

12... p-InP cladding layer, 13...
Undoped 1nGaAsP (15% @, 14
”-n-1nP Kufud 1m.

15...8i0zk, 16...C
dz forgiveness front.

17...-Cd diffusion region, 18...
p-type electrode.

19・・・・・・〇9 Indicates n-type 'wL&
! Color-Arm ~O

Claims (1)

[Claims] A three-layer structure in which at least a first cladding layer and an active layer of @l conductivity type and a second cladding layer and a second cladding layer of a second conductivity type are sequentially formed on an insulating substrate whose surface has a step-like shape, At least the first cladding layer and the active layer have surfaces that maintain the step-like shape, and further include a region doped with an impurity exhibiting @1 conductivity in a flat region away from the step-like step portion. The impurity doped region is formed to a depth of 6 from the surface of the Igtr layer to the first cladding layer, and the surface of this impurity doped region and
Semiconductor laser with an electrode on the surface layer of the @2 layer corresponding to the upper part of the stepped film difference part〇