JPS641072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried heterostructure semiconductor laser in which an active layer is surrounded by a semiconductor material having a larger energy gap and a lower refractive index.

Buried heterostructure semiconductor laser (BH-LD)
Because it has excellent properties such as a low oscillation threshold current, a stabilized oscillation transverse mode, and the ability to operate at high temperatures, it is attracting attention as a light source for optical fiber communications. As shown in Japanese Patent Application No. 56-166666, the inventors of the present application have reliably developed a method other than a mesa stripe that includes an active layer that recombines light and is sandwiched between two substantially parallel grooves. Invented an In _{1-x Ga x} As y P _1-y BH-LD that can form a current blocking layer, has excellent temperature characteristics, is less susceptible to damage during various substrate processing processes, and has improved manufacturing yields. did. However, in a BH-LD with this structure, if the width of the groove between the mesa stripes containing the active layer that undergoes luminescent recombination is small, the growth rate of the current blocking layer is high in that part, and the p-InP current blocking layer, When laminating the n-InP current blocking layer, the n-InP current blocking layer may grow continuously on the top of the mesa stripe.
This resulted in a decrease in yield. In addition, if the width of the groove is increased to prevent this, the breakdown voltage of the current blocking layer in the groove part cannot be maintained sufficiently, which may increase the leakage current of the BH-LD and cause variations in characteristics. Ta.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, and to provide a BH that has a high breakdown voltage of the current blocking layer, good reproducibility of crystal growth, and significantly improved manufacturing yield.
- To provide LD.

According to the present invention, a multilayer structure semiconductor wafer in which a semiconductor multilayer film including at least an active layer and a second conductivity type semiconductor clad layer is grown on a first conductivity type semiconductor substrate is mesa-etched to a depth deeper than the active layer. In a buried heterostructure semiconductor laser that is formed by forming a stripe and then growing the mesa stripe, a mesa stripe containing an active layer that recombines light is sandwiched between two grooves, and a second conductive layer is formed at the bottom of the two grooves. A first conductivity type semiconductor current blocking layer is formed except for only the upper surface of the mesa stripe, and a semiconductor layer having a smaller energy gap than the first conductivity type semiconductor current blocking layer is formed over the entire surface. As a result, a buried heterostructure semiconductor laser characterized in that buried layers of the second conductivity type are sequentially laminated is obtained.

The present invention will be explained below using drawings showing examples.

FIG. 1 is a sectional view of a BH-LD according to an embodiment. To obtain such a BH-LD, first, an n-InP buffer layer 102 is formed on a (100) n-InP substrate 101, and a non-doped layer corresponding to an emission wavelength of 1.3 μm is formed on the (100) n-InP substrate 101.
In _0.72 Ga _0.28 As _0.61 P _0.39 Two grooves 152 and 15 are formed in parallel to the <011> direction in a multilayer structure wafer in which an active layer 103 and a p-InP cladding layer 104 are sequentially laminated.
3 and mesa stripes 151 sandwiched between them. The width of the grooves 152 and 153 is
The width of the mesa stripe 151 is 2 μm.
Next, a Zn diffusion region 105 is formed while leaving the SiO ₂ film used as an etching mask for the trench. When forming this Zn diffusion region 105, first
- After removing the InP cladding layer by selective etching, Zn is diffused, and after the diffusion In _0.72 Ga _0.28
As _0.61 P _0.39 Selective etching of the active layer results in good melt wetting during the subsequent buried growth, and good crystal growth reproducibility. Embedded growth is performed on the multilayer structure semiconductor wafer obtained in this way,
The n-InP current blocking layer 106 is removed from the top surface of the mesa stripe, followed by the p-In _0.72 Ga _0.28 As _0.61 P _0.39 layer 107, which corresponds to the emission wavelength of 1.3 μm, and the p-InP buried layer 108, which corresponds to the emission wavelength of 1.1 μm. p-
In _0.85 Ga _0.15 As _0.33 P _0.67 electrode layer 109 is laminated to obtain the desired BH-LD. In addition, at this time p-In _0.72
Ga _0.28 As _0.61 P _0.39 Layer 107 is mesa stripe 15
It does not matter if the top surface of 1 is covered. It may also be n-type, but in this case, the mesa stripe 15
Do not cover the top of 1. this
In _1-x Ga _x As _y P _1-y /InP In BH-LD, the two parallel grooves 152 and 153 sandwiching the mesa stripe 151 have a slightly wider width of 10 μm, so the groove During buried growth after etching, the current blocking layer rarely covers the mesa stripe 151, and the reproducibility of crystal growth is improved. In addition, in the conventional example, when the width of the two grooves is widened, the p-n-p-n
Because the breakdown voltage of the structure was not high enough, variations in characteristics sometimes occurred.
p-In _0.72 on top of n-InP current blocking layer 106
By stacking the Ga _0.28 As _0.61 P _0.39 layer 107, the current gain of the p-n-p transistor formed from the epitaxial growth layer side can be reduced, so the breakdown voltage can be made sufficiently high in this area as well. It can be used and has good characteristics.

In an embodiment of the invention, mesa stripe 1
The current blocking layer structure of the groove portions on both sides of 51 is n-InP/p-InP/n-InP/p-In _0.72 Ga _0.28
Since the layer structure As _0.61 P _0.39 /p-InP is applied, the breakdown voltage of the p-n-p-n current blocking structure can be maintained sufficiently high even in this groove portion. Therefore, the two parallel grooves 152 and 153 sandwiching the mesa stripe 151 can be made wider, which reduces the possibility that the current blocking layer covers the mesa stripe during buried growth, making it easier to reproduce crystal growth. Sexuality also improved.

In the example, a BH-LD in the 1 μm wavelength band using an InP substrate with In _1-x Ga _x As _y P _1-y as the active layer was used.
However, the present invention is not limited to this material system, and can be applied to other semiconductor materials. Furthermore, the conductivity type of the semiconductor layer may be such that all p and n conductivity types are changed.

The feature of the present invention lies in the current blocking layer structure of the grooves on both sides of the mesa stripe containing the active layer that emits and recombines. This is because semiconductor layers with small gaps are stacked.
This allows the breakdown voltage of the current blocking layer structure in the trench to be sufficiently high, making it possible to widen the trench, thereby preventing the current blocking layer from covering the mesa stripe during buried growth. This also improved the reproducibility of crystal growth.

[Brief explanation of the drawing]

Figure 1 shows an example of In _1-x Ga _x As _y P _1-y /InP
It is a sectional view of BH-LD. In the figure, 101... n-InP substrate, 102... n-
InP buffer layer, 103...In _0.72 Ga _0.28 As _0.61
P _0.39 active layer, 104...p-InP clad layer, 1
05...Zn diffusion region, 106...n-InP current blocking layer, 107...p-In _0.72 Ga _0.28 As _0.61 P _0.39
Layer, 108... p-InP buried layer, 109...
p-In _0.85 Ga _0.15 As _0.33 P _0.67 Electrode layer, 110...p
111 is an n-type ohmic electrode.

Claims (1)

[Claims] 1 At least an active layer on the first conductivity type semiconductor substrate,
In a buried heterostructure semiconductor laser, a multilayer structure semiconductor wafer on which a semiconductor multilayer film including a semiconductor cladding layer of a second conductivity type is grown is mesa-etched deeper than the active layer to form a mesa stripe, and then buried and grown. The mesa stripe including the active layer that undergoes luminescent recombination is sandwiched between two grooves, and a second conductivity type semiconductor region is formed at the bottom of the two grooves, and only the upper surface of the mesa stripe is sandwiched between two grooves. A semiconductor current blocking layer of a first conductive type is formed except for the semiconductor current blocking layer of the first conductive type, and a buried layer of a second conductive type is sequentially laminated over the entire surface of the semiconductor layer having a smaller energy gap than the semiconductor current blocking layer of the first conductive type. A buried heterostructure semiconductor laser characterized by: