JPS595690A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To facilitate high output power operation and to improve a characteristic yield, in semiconductor laser having a heterogeneous structure, by forming a current block layer structure at a part where the layer is closer to a substrate than an active layer, in addition to a current block layer, which is formed on both sides or in the vicinity of the active layer. CONSTITUTION:A mesa stripe 102 is formed on an N type InP substrate 101. On the substrate 101, a P type InP layer 103, an N type InP clad layer 104, a nondoped In0.72Ga0.28As0.61P0.39 active layer 105 corresponding to an oscillating wavelength of 1.3mum, and P type InP clad layer 106 are sequentially laminated by a liquid phase epitaxial method. In this case, the P type InP layer 103 is not grown on the upper surface of the mesa stripe 2. Mesa etching is performed on said semiconductor wafer. Two etching grooves 107 and 108 and a mesa stripe 109, which separates the grooves, are formed at this time. Embedded growing is performed in the semiconductor wafer, wherein the mesa stripe 109 is formed. Then, a P type InP current block layer 110 and an N type InP current block layer 111 are laminated all-over except only on the surface of the mesa stripe 109. Thereafter, a P type InP embedded layer 112 and an electrode layer 113 are laminated, and finally an electrode is formed.

Description

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

Buried heterostructure semiconductor lasers (BH-LDs) have excellent characteristics such as low oscillation threshold current, stabilized oscillation transverse mode, and high-temperature operation, so they are attracting attention as light sources for optical fiber communications. are collecting. As shown in Japanese Patent Application No. 56-166666, the inventors of the present application have ensured that a current blocking layer is formed around a mesa stripe containing an active layer that recombines light and is formed between two substantially parallel grooves. We have invented a BH-LD that can form . This BH-L
D has excellent temperature characteristics, is less susceptible to damage during various substrate processing processes, and has an improved manufacturing yield. By the way, not only BH-LD in this example, but BH-LD in general
- In LD, leakage current is a problem that cannot be completely eliminated. The above-mentioned BH-LD is also a BH of other types.
-LD also generally uses a semiconductor p-n-p-n current block structure to reduce leakage current as much as possible. However, when attempting to operate with a high optical output of 59 mW or more on one side, the leakage current flowing beside the buried active layer also increases. This leakage current then becomes the gate current in the p-rl-pn current block structure described above, causing breakdown of the current block structure. Correspondingly, the light output also saturates rapidly, and no matter how much the injection current is increased, the light is not effectively injected into the active layer, making it impossible to obtain a high light output. In order to improve such high-output operating characteristics, attempts have been made to cover the area other than the upper part of the active layer with an insulating film, or to diffuse impurities only in the upper part of the active layer, creating a so-called Brenna stripe structure. If it is difficult and has poor reliability, or if the internal current block structure no longer functions effectively, the current will spread greatly toward the substrate side. In other words, in conventional BH-LDs, in contrast to the current blocking structure near the active layer, the current narrowing mechanism was provided on the surface side of the growth layer, so once the pn-pn current blocking structure around the active layer If it no longer works effectively, the optical output will suddenly become saturated. To prevent this, it is sufficient to form another current blocking mechanism closer to the substrate than the active layer.

An object of the present invention is to provide a BH-LD with high manufacturing yield and improved high optical output operating characteristics.

The semiconductor laser according to the present invention has a structure in which a semiconductor wafer has a multilayer film structure in which a semiconductor multilayer film including at least an active layer is laminated on a semiconductor substrate, and is sandwiched between two parallel grooves formed deeper than the active layer. In the buried heterostructure semiconductor laser formed by forming a mesa stripe and then growing the buried heterostructure semiconductor laser, the multilayer structure semiconductor wafer comprises:
It is characterized by having a current block structure in which semiconductor layers of different conductivity types are alternately stacked except at least around the mesa stripe.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated using drawing which shows an Example.

FIG. 1 shows a schematic diagram showing the manufacturing process of a BH-LD which is a first embodiment of the present invention. To obtain such H-LD, first, as shown in (1) in the figure, (100) n-In
Mesa stripes 102 are formed on a P substrate 101 in parallel to the <011> direction. The mesa stripe 102 may have a width of about 10 μm and a depth of about 1 μm.

This can be easily formed by ordinary photophosphorography techniques and chemical ching methods. This mesa stripe 10
On the n-InP substrate 101 on which 2 is formed, a p-1 nP layer 103 is formed by liquid phase epitaxial method (LPE method).
, n-InP cladding layer 104, non-doped Ino72 Gao, zs A50 corresponding to an oscillation wavelength of 1.3 μm
．． 6IP0.39 The active layer 105 and the p-InP cladding layer 106 are sequentially laminated. At this time, the p-InP layer 10
3 should not grow on the upper surface of the mesa stripe 102. This is one of the characteristics of liquid phase growth, and occurs because the side surfaces of the mesa stripe grow quickly, so there are fewer P atoms near the top surface of the mesa, and the degree of supersaturation of the solution becomes smaller. In practice, a device was fabricated in this manner, but for other devices, for example, after growing the p-1nP layer 103, the upper surface of the C mesa stripe 102 was lightly melted back using a solution with an extremely low degree of supersaturation. In this way, a desired semiconductor wafer can be obtained even if the p-InP layer 103 is also stacked on the upper surface of the mesa. The thickness of each semiconductor layer is 3 a for the n-InP cladding layer 104.
m, In O, 72Gao2s ASo, 61P0
The thickness of the 39 active layer 105 is 0.15 μm, and the thickness of the p-InP cladding layer 106 is about 1 μm. Next, the semiconductor wafer thus obtained is subjected to mesa etching as shown in FIG. 1(2). At this time, two pieces of width 10μm and depth 3μm
Etched grooves 107, 108 and a mesa stripe 109 sandwiched between them are formed. The mesa stripe 109 is parallel to the (011> direction, and the mesa stripe 109 is rubbed so that it is located above the first mesa 102.The semiconductor wafer on which the mesa stripe 109 has been formed in this way is buried and grown as desired. B of
1-1-LD is obtained. In the case of embedded growth, p −
InP current blocking layer 110. All n-InP current-current bluffs 111 are stacked except for the top surface of the mesa stripe 109. Furthermore, a p-InP buried layer 112, a p-InP layer corresponding to an emission wavelength of 13 μn1
7z Gao28AS0.61 Po, 39 electrode layer 11
3 is laminated over the entire surface, and finally electrodes are formed.

The BH-LD obtained in this way has a CW oscillation threshold current of 20 mA at room temperature, a differential quantum efficiency of 60 cm, and an optical output from one side of 5 Q mW or more, resulting in a device with good linearity of the I-L characteristic with good reproducibility. Obtained. In this first embodiment, p-InP current current bluff 22 layers 110-InP current current bluff 2 layers 111 are formed in the buried growth stage.
A current blocking layer structure constituted by the p-InP layer 103 was previously formed inside the device. As a result, the leakage current of the BH-LD has been significantly reduced, and high output operation can now be achieved with extremely high reproducibility. In other words, with respect to the current blocking layer structure near the active layer, since the current blocking layer structure is formed closer to the substrate than the active layer, the leakage current when large current is injected can be significantly reduced, resulting in high output operation of BH-LD. became possible.

FIG. 2 shows a second embodiment of the invention. In this case, the first
This embodiment differs from the embodiment in that the p-InP layer 103 is formed by impurity diffusion before epitaxial growth. That is, after selectively diffusing impurities on the n-1nP substrate 101 to form the p-InP layer 103, a semiconductor multilayer film is laminated. Mesa stripes 109 are formed in areas other than where the p-InP layer 103 is formed, as in the first embodiment. In the first embodiment, the p-InP layer 103 was epitaxially grown selectively on areas other than the wide mesa stripe 102 formed on the n-InP substrate 101, but in the second embodiment, a selective diffusion method was used. The ease of manufacture was further improved. In this second embodiment as well, a current blocking layer structure is formed inside the substrate in addition to both sides of the active layer, making it easy to obtain high output operation of the BH-LD. Ta. In this case as well, a BH-LD with characteristics comparable to those shown in the first example was obtained with good yield.

In addition, in the two embodiments of the present invention, both In
P as a substrate and In5-z G with lattice matching to it.
As Asy Although a device with a wavelength band of 1 μm is shown in which the active layer is an active layer, the semiconductor material used is of course not limited to this, and semiconductor materials in the visible light region or semiconductor materials in the wavelength region of around 2 μm can be used. Even if there is, of course it can't be ruled out. Regarding the conductivity type of the semiconductor, an n-type substrate was used, but a p-type substrate may be used to reverse the conductivity types of all other semiconductor layers, and the current blocking layer may be a p-type substrate.
Although the basic structure is based on a current blocking effect using a -n junction, an i-layer or an amorphous semiconductor layer may be used as a current blocking layer. In the example, a simple H-LD structure was shown, but DFB-BH-LD and DBR-BH-L using a diffraction grating as a single mode LD
DL, FD for monitor, and FET for driver.

The present invention can also be applied to a BH-LD in which transistors and the like are decoded.

The feature of the present invention is that in the BH-LD, both sides of the active layer,
Or in addition to the current blocking layer formed around it,
The current blocking layer structure is formed on the side closer to the substrate than the active layer. This resulted in the formation of a double current blocking layer structure, which significantly reduced the leakage current flowing through both sides of the active layer, especially when a large current was injected. Therefore, high output operation of the BH-LD has become much easier than in the conventional type, and the characteristic yield has also improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the manufacturing process of B1-1-LD, which is the first embodiment of the present invention, and FIG. 2 is a sectional view of BH-LD, which is the second embodiment. In the figure, 101 is n-I
nP substrate, 102 is mesa stripe, 103 is p-In
P layer, 104 is n-InP cladding layer, 105 is Ino
, yz Gao, zs ASQ, 61 Po, 39 active layer, 106 is p-InP cladding layer, 107, 108
109 is an etched groove, 109 is a mesa stripe containing an active layer, 110 is a p-1nPil;
-1nP current blocking layer, 112 is p-InP buried layer, 113 is p-In0.72Gao2s ASo, 6
1 Po, 39 electrode layers respectively.

Claims (1)

[Claims] A mesa stripe sandwiched between two parallel grooves formed deeper than the active layer is formed on a multilayer semiconductor wafer in which a semiconductor multilayer film including at least an active layer is laminated on a semiconductor substrate, and then buried. A buried heterostructure semiconductor laser having a current block structure in which conductive type semiconductor layers, which are grown buried heterostructure semiconductor layers, are alternately stacked.