JPH09298334A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the threshold of an buried hetero-junction laser by burying and growing a first conductivity type semiconductor layer and second conductivity type semiconductor layer, diffusing a dopant into the surface of this semiconductor layer to change it to a first conductivity type one and burying and growing a first and second conductivity semiconductor layers. SOLUTION: A p-type clad layer 2 is grown on a p-type substrate 1 and an undoped MQW active layer 3 an n-type clad layer 4 are grown. A SiO2 film 15 is deposited. After a photolithographic step, a mesa stripe having smooth side faces is formed by etching while using this film 15 as a mask. Its side faces are filled with a Zn-doped p-type InP layer 5 and Si-doped n-type InP layer 6 to form a p-type Zn diffused layer 7 on the surface of the InP layer 6. A Zn-doped p-type InP layer 8 and Si-doped n-type InP layer 9 are grown and the mesa stripe is buried. The SiO2 film is removed and n-type InP layer 10 and n-type InGaAs cap layer 11 are buried flat.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a buried heterostructure semiconductor laser.

[0002]

2. Description of the Related Art In order to reduce the threshold of a semiconductor laser, it is essential to reduce the leak current flowing in regions other than the active region. Conventionally, in a buried hetero (BH; Burried Heterostructure) laser, a pn junction or a high resistance semiconductor layer (Fe and Ti doping, etc.) is used as a current blocking layer,
An example of a BH laser using ap substrate is
Letters Volume 28 Number 19 1992 184
Page 4 (Electronics Letters Vol.28 No.19 1992 p.18
44), metal organic chemical vapor deposition (MOCVD;
There is a pn junction buried type BH laser by the Metalorganic Chemical Vapor Deposition method.

[0003]

When a BH laser with a pn junction is buried in the prior art, the n-type InP buried layer 6 and the n-type InP layers 9 and 10 are easily connected as shown in FIG. nn connection is easily formed), and a current cannot be reduced sufficiently because the current flows through the nn connection.

In the figure, 1 is a p-InP substrate, 2 is a p-InP clad layer, 3 is an MQW active layer, 4
Is an n-InP clad layer, 5 is a p-InP layer, and 8 is a p-
InP layer, 11 is n-InGaAsP cap layer, 12
Is an SiO ₂ film, 13 is an n-electrode, and 14 is a p-electrode.

An object of the present invention is to achieve a low leakage current buried structure without such an nn connection, thereby achieving BH.
The object is to reduce the threshold of the laser.

[0006]

Means for achieving the above object will be described with reference to FIG. A mesa stripe having a smooth side surface shape without an inflection point is formed, and by the buried growth thereof, first the Zn-doped p-type InP layer 5 and then the Si-doped n-type InP layer 6 (n-InP block layer) are formed. Grow continuously. Next, in the same growth apparatus (MOCVD apparatus), Zn
Are diffused to form the p-type InP layer 7 as the surface layer. Then
Even if the growth front of the block layer reaches the top of the mesa, the surface layer becomes the p-type InP layer 7. Therefore, the buried block layer 6 is completely separated from the n-type InP layer 9 or 10 which is to be grown thereabove, and is surrounded by the p-type InP layers 5, 7 and 8 having low mobility. Become.

With such a structure, a leak current flowing in a region other than the active region of the mesa stripe is effectively suppressed, and a low threshold semiconductor laser can be realized.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where the present invention is applied to an InGaAsP-based BH laser will be described with reference to FIGS.

By the metal organic chemical vapor deposition (MOCVD) method, the p-InP substrate 1 (carrier concentration 4 to 6 × 10 ¹⁸ cm
² ) the p-InP clad layer 2 (carrier concentration ~ 1 x 10
¹⁸ cm ~ ² , thickness ~ ² μm) and then undoped InG
aAsP / InGaAs MQW active layer 3 (wavelength 1.3
μm, thickness ~ 0.2 μm), n-InP clad layer 4
(Carrier concentration of 2 × 10 ¹⁸ cm ² and thickness of 1 μm) is grown. At this time, the active layer 3 may be an AND-type InGaAsP bulk active layer and is not limited to the MQW structure.

After that, a SiO ₂ film 15 is deposited by the CVD method, and a photolithography process is performed. Then, by wet etching using the SiO ₂ film 15 as a mask, a mesa having a smooth side surface having no inflection point as shown in FIG. 3 is formed. Forming stripes. The mesa stripe is formed such that the lower part of the SiO ₂ film 15 is etched from the side surface so that the SiO ₂ film 15 has an overhang shape. The active layer width is 1 to 2 μm and the mesa depth is 2.5 to 4 μm.

Next, by MOCVD, the side surface of the mesa stripe is Zn-doped p-I while the SiO ₂ film is deposited.
nP layer 5 (carrier concentration ~1 × 10 ¹⁸ cm ~ ^2, a thickness of 0.5
˜1 μm), and Si-doped n-InP layer 6 (carrier concentration ˜2 × 10 ¹⁸ cm- ² , thickness 0.5-1 μm).

Thereafter, dimethyl Zn (DMZn) was placed in the growth chamber.
And phosphine (PH ₃ ) are introduced to form a p-type Zn diffusion layer 7 on the surface of the n-InP layer 6. At this time, the diffusion is MO
The sample is exposed to air and is not contaminated because it is performed continuously with embedded growth in the CVD device. Although DMZn was used as the Zn diffusion source here, diethyl Z
n (DEZn) may be used.

Next, the Zn-doped p-InP layer 8 (carrier concentration: 2 × 10 ¹⁸ cm- ² , thickness: 1-3 μm), the Si-doped n-InP layer 9 (carrier concentration: 2 × 10 ¹⁸ cm- ² , The thickness was grown to 0.5 μm) and the mesa stripe was embedded.
The n-InP layer 9 is provided to separate the pn junction from the regrowth interface, and the insertion is not particularly limited in the present invention.

Next, after removing the SiO ₂ film, the n-InP
Layer 10 (Carrier concentration ~ 2 × 10 ¹⁸ cm ~ ² , Thickness ~ 2μ
m), n-InGaAsP cap layer 11 (carrier ^{concentration> 5 × 10 18 cm ~ 2} , but flat buried in thick ~2μm).

In the structure buried as described above, even if the growth front of the n-InP layer 6 reaches the top of the mesa, its surface layer becomes the p-type InP layer 7 in which Zn is diffused. . Therefore, the embedded n-type InP layer 6
The (n-InP current blocking layer) is completely separated from the n-type InP layers 9 and 10 and has a low mobility around the p-type I layer.
An ideal block layer structure surrounded by the nP layers 5, 7 and 8 is obtained. In such a structure, a leak current flowing in areas other than the active region of the mesa stripe is effectively suppressed, and a low-threshold semiconductor laser can be realized.

After that, the SiO ₂ film 12 was used to confine the current, and then the n-electrode 13 was formed. Further, the substrate side was polished to a total film thickness of about 100 μm, and then the p-electrode 14 was formed by vapor deposition to form a device. .

In the BH laser according to this embodiment, the oscillation wavelength is 1.3 μm, the threshold current value is 10 to 12 mA, and the slope efficiency is 0.3.
An element of mW / mA 2 was obtained with a high yield, and a semiconductor laser with a low leak current and a low threshold could be realized.

In this embodiment, the application to the semiconductor laser has been described. However, the present invention is not limited to the semiconductor laser and can be applied to other devices that require current confinement.

[0019]

As in the present invention, a mesa stripe having a smooth side surface without an inflection point is embedded by a pn junction, and Zn is grown after the growth of the n-InP current blocking layer.
Is diffused, the surface of the block layer becomes a p-type InP layer. Therefore, even if the growth front of the block layer reaches the top of the mesa, the nn connection can be eliminated, the leak current is small, and a low threshold element for efficiently injecting current into the active region can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser showing one embodiment of the present invention.

FIG. 2 is a sectional view of a semiconductor laser showing a conventional example.

FIG. 3 is an explanatory diagram of a main part of one embodiment of the present invention.

[Explanation of symbols]

1 ... p-InP substrate, 2 ... p-InP cladding layer, 3 ...
MQW active layer, 4 ... n-InP cladding layer, 5 ... pI
nP layer, 6 ... n-InP layer, 7 ... Zn diffusion p-InP
Layer, 8 ... p-InP layer, 9 ... n-InP layer, 10 ... n-
InP layer, 11... N-InGaAsP cap layer, 12
... SiO ₂ film, 13 ... n electrode, 14 ... p electrode, 15 ... S
iO ₂ film.

Claims (4)

[Claims] 1. A multi-layered structure including an active layer is formed on a semiconductor substrate, and the multi-layered structure is processed into a mesa stripe shape having a smooth curved surface with no inflection point, and the mesa side surface is formed of a first conductivity type. A semiconductor device embedded with a semiconductor multilayer film including a semiconductor layer of a second conductivity type and a semiconductor layer of a second conductivity type.
After a conductive type semiconductor layer and then the second conductive type semiconductor layer are embedded and grown, a dopant having the semiconductor layer as the first conductive type is diffused from the surface, and then the first conductive type and the second conductive type are further diffused. A semiconductor device, wherein a conductive type semiconductor layer is embedded and grown. 2. The MOCVD apparatus according to claim 1, wherein first the semiconductor layer of the first conductivity type and then the semiconductor layer of the second conductivity type are buried and grown first, and then the same is grown from the surface in the same apparatus. A method of manufacturing a semiconductor device, wherein a dopant having a semiconductor layer as a first conductivity type is diffused, and then the semiconductor layers of the first conductivity type and the second conductivity type are further embedded and grown. 3. A multi-layer structure including an active layer is formed on a p-type InP substrate, the multi-layer structure is processed into a mesa stripe shape having a smooth curved surface with no inflection point, and the mesa side surface is Z-shaped.
In a semiconductor laser device embedded with an n-doped p-type InP layer and a Si-doped n-type InP layer, p-type InP is first
A semiconductor laser device, wherein a layer, then an n-type InP layer is buried and grown, Zn is diffused from the surface, and then p-type and n-type InP layers are further buried and grown. 4. The MOCVD apparatus according to claim 3, wherein first, the p-type InP layer and then the n-type InP layer are grown by burying, and then Zn is diffused from the surface in the same apparatus. A method for manufacturing a semiconductor laser device in which the p-type and the n-type InP layers are embedded and grown.