JPS61164287A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a high photo output in a semiconductor laser by a method wherein a p-type substrate is used for the semiconductor laser, the p-type clad layer and a p-type current blocking layer come into contact to each other on the side surface of the mesa striped mount and a semiconductor layer with the small forbidden band width gap is introduced in on the p-type current blocking layer. CONSTITUTION:A p-type InP clad layer 2, an active layer 3 and an n-type InP clad layer 4 are laminated in order on a p-type InP substrate 1. After that, a mesa striped mount 10 is formed. After that, an n-type InP current blocking layer 5, a p-type InP current blocking layer 6 and an In0.78Ga0.22As0.48P0.52 layer 11 are laminated in order excluding the upper surface of the mesa striped mount 10. Then, an n-type InP buried layer 7 and an n-type In0.78Ga0.22As0.48P0.52 electrode layer 8 are laminated over the whole surface. An InGaAsP layer 11 with the small forbidden band width gap is inserted in between the layers 6 and 7, whereby the current gain of the transistor becomes smaller, the turn-ON withstand voltage of the thyristor is not affected so much by the gate current and even when a leakage current 9 runs on the thyristor to some degree, the thyristor is never turned-ON. As a result, injecting current runs effectively into the active layer 3.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a buried heterostructure semiconductor laser.

(Prior art and its problems) Buried heterostructure semiconductor lasers (BH-LDs) have excellent characteristics such as low oscillation threshold current, stabilized oscillation transverse mode, and high-temperature operation. Practical use is progressing as a light source for original fiber communications. - It is hoped that submarine relay optical fiber communication will be put into practical use as a long-distance, high-capacity intercontinental communication system, but the development of an ultra-highly reliable semiconductor laser that is unprecedented for its practical use is required. has become a particularly strong demand.

Conventionally, BH-LDs with various structures have been prototyped, but most of them have mainly used n-type InP substrates. In this
In this method, an InGaAsP active layer is grown on an InP type and operates at an oscillation wavelength of 1.3 μm to 155 μm.
The conditions for forming the electrodes, which have the most important effect on the reliability of the LD, are strict. That is, in order to reduce the ohmic resistance, InGa
- AsP layer is used as an electrode layer, and p of 1×10 crn or more is formed by impurity diffusion or doping during crystal growth.
The metal electrode was formed with V's type impurity concentration and AuZn, TiPt, or CrAu.

In this case, for any electrode material, 400°C to 50°C
Heat treatment was applied at a temperature range of about 0°C.

In such a heat treatment process, the electrode metal material penetrates into the semiconductor layer or stress is introduced, which is considered to have lowered the reliability of the collector.

On the other hand, a highly reliable LD with easy electrode formation has recently been produced by crystal growth on a p-type InP substrate.
Several cases of H-LD have been reported. They mainly form an active layer buried in the V-groove, and are difficult to apply to distributed feedback (DFB) semiconductor lasers and distributed Bragg reflection (DBR) semiconductor lasers, and are difficult to apply to distributed feedback (DFB) semiconductor lasers and distributed Bragg reflection (DBR) semiconductor lasers, and are based on single-axis mode characteristics. Long-distance, large-capacity transmission cannot be fully realized. In addition to this, a Bi(-LD) with a mesa-embedded structure using a p-type InP substrate has been prototyped, but due to an inappropriate current blocking layer structure, there is a large amount of current leakage to areas other than the active layer. However, good characteristics are not obtained.

(Conventional Example) FIG. 5 is a cross-sectional view of a conventional mesa structure BH-LD using a p-type substrate. In this case, K on the p-InP substrate 1
p-InP cladding layer 2. InGaAsP active layer 3
．． After sequentially laminating the n-InP cladding layer 4, the entire mesa stripe 10 is formed by etching, and then the n-InP'E+A block layer 5 is formed by buried growth. p-
Both 4nP current blocking layers 6 are mesa stripes 10
Except for only the top surface, an n-InP buried layer 7 was further grown over the entire surface to form an InGaAsP electrode layer 8. From the viewpoint of transverse mode control, 1.
The thickness was 5 μm and the thickness was 01 μm.

When a positive voltage is applied to the p-side electrode of this BH-LD, a current flows through the active layer 3, and laser rooting occurs above a threshold value due to radiative recombination of carriers. In this case, in addition to the active layer 3, leakage current IL may flow through the current blocking layer 6 as shown in the path of the arrow in the figure. Such leakage current IL flows into the buried layer 7 as shown by the arrow in the structural diagram of the current blocking layer 6 shown in FIG.

Since this has a 1InP npnp thyristor structure, it acts as a gate current, significantly lowering the breakdown voltage. That is, in the conventional structure shown in FIG. 5, there was a problem in that if the injected current was increased beyond a certain level, only the leakage current IL would increase, making it impossible to extract a large optical output.

In the example shown in FIG. 5, although the oscillation threshold current is as low as about 20 mA at a wavelength of 1.3 μm, the saturation tendency of the optical output is strong, and it is difficult to obtain an optical output of 30 mW or more.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned problems and to provide a buried heterostructure semiconductor laser with good characteristics and high reliability.

(Structure of the Invention) The structure of the present invention is a multilayer structure semiconductor wafer in which a semiconductor multilayer film having an active layer sandwiched between at least p-type and n-type cladding layers is laminated on a semiconductor substrate. In a semiconductor laser with a buried heterostructure formed by forming a mesa stripe between the active layer and the active layer, and growing the mesa stripe in a buried manner, the n-type current blocking layer and the side surfaces of the mesa stripe, except for the top surface of the mesa stripe, p in contact with the p-type cladding layer at
A p-type current blocking layer is formed, and a semiconductor layer having a small bandgap is also formed on the p-type current blocking layer.

(Principle of the Invention) In the present invention, leakage current can be suppressed to a low level by making the npnp silicon risk structure not significantly affected by gate current and having a sufficiently large breakdown voltage. This means that it can operate stably up to high output. To this end, a semiconductor layer with a small bandgap is introduced on the current blocking layer to reduce the current gain of the npn or pnp transistor constituting the thyristor.

(Example) Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a structural sectional view of a BH-LD which is the first W flow side of the present invention. To obtain this BH-LD, first, as in the conventional example, a p-InP cladding layer 29 is coated with non-doped InO corresponding to an emission wavelength of 1.3 μm on a p-InP substrate 1.
, 72GaO, 2BAsO061po, 39 active layers 3 with a thickness of 0 and 111 m, and an n-InP cladding layer 4f with a thickness of 1 μm. Mesa stripes 10 are then formed using conventional chemical etching techniques. This mesa stripe 10 has a depth of 3 μm and an active layer 3 with a width of 1.5 μm.
It was formed so that it became m. Thereafter, an n-1nP current blocking layer 5 is formed to a thickness of approximately 0.0 mm except for the upper surface of the mesa stripe 10.
7 μmt pLnP current blocking layer 6 approximately 2 μm thick
.

Non-doped I n O corresponding to an emission wavelength of 1.2 μm
, 78Ga0, 22AS0.48P0.52 layers 11 were sequentially laminated to a thickness of about 0.2t1m, and then n
-InP buried layer 7, emission wavelength 12μ always corresponds to n
-In O,78Gao22A 80.48 Po,5
Two electrode layers 8 were laminated.

In this case as well, the leakage current IL i flowing to the side of the active layer 3
d. The current flows along the path indicated by the arrow in the figure, and acts as the gate current of the 1/J-pnpn structure thyristor as in the conventional example. However, in this case, as shown in Figure 3, b
Since the InGaAsP layer 11 with a small bandgap is inserted into the npn transistor constituting the l''pn thyristor, the current gain of the transistor is small, so that the turn-on withstand voltage of the thyristor is not affected by the gate current. Even if the leakage current 9 flows to some extent, it will not turn on, and the injected current will effectively flow into the active layer 3.

When a BH-LD with such a structure was cut out with a length of 300 μmF, the oscillation threshold current at room temperature CWVt- was 20 mA, the differential singleton efficiency was 60%, the oscillation was performed in the transverse fundamental mode up to 60 mW or more, and the maximum CW operating temperature was as 120℃
Reproducibility of some degree was obtained.

A TiPtAu-based electrode is formed on the n side of this element, and
Even though the heat treatment was performed at a low temperature of 0° C., a sufficiently low value of collector resistance of about 40 was obtained.

In addition, when mounted on a diamond heat sink using AuSn flux, 5 mW at 70°C and 10 mW at 70°C were applied.
When we conducted a reliability test of constant light output drive, the deterioration rate was 1 to 2 x 10 = H-1, 4 to 5 x 10, respectively.
-'H-1 was found to be approximately 10 times more reliable than the conventional element. Furthermore, when we fabricated a DFB-LD using this structure by forming a guide layer with a diffraction grating adjacent to the active layer 3, single-axis mode oscillation of up to 68 mW was obtained at room temperature CW operation, and furthermore, a Farpry-Perot laser We obtained highly reliable results equivalent to

FIG. 2 shows a second embodiment of the present invention.
A cross-sectional view is shown. In this case as well, the entire double heterostructure including the entire active layer 3 was formed on the p-1nP substrate 1, and mesa etching was performed. However, in this case, the n-I n P cladding layer 4 has a thickness of 2 trm, n-Ino, 7aGa
o, 2zASo, 4sP0.52 electrode layer 11 with thickness 05
μm is formed, etched into an inverted mesa structure, and this mesa stripe is 1° = 3.5/j? It was about 7L deep. p-InP current blocking layer 6 mesa stripe 10
It was made to contact the p-InP cladding layer 2 at the side surface.

Further, the final layer of buried growth was a p-InP cap layer 12.

In this embodiment, only the mesa stripe 10 portion of the surface of the shrimp growth layer is n-type, and the rest is n-type. For example, if a TiPtAu electrode is formed, p-In
Since a Schottky barrier is formed between the P cap layer 12 and the electrode, the capacitance component can be made sufficiently small in this portion. Therefore, even with a full-surface electrode structure, high-speed @contact modulation of IGb/s or higher is fully possible. In this case, the leakage current IL will flow along the path shown by the arrow in the figure, but in this case as well, the thyristor structure contains InGaAs with a small band gap.
Because the P layer 11 is formed, it is difficult to turn on,
Therefore, the BH operates stably up to high optical output levels.
-LD was obtained. Similarly, when a laser pellet was cut out and its characteristics were evaluated, results with high performance and high reliability almost equivalent to those shown in the first example were obtained.

In addition, on the flood disaster side, all InP substrates, InG
Although a device with a wavelength band of 1 μm as an a-AsP fz active layer is shown, the device is not limited to this, and GaA7As/
There is no problem in using other semiconductor materials such as GaAsInGaA and s/AjInAs. Furthermore, on the water disaster side, a structure in which all parts other than the mesa stripe 10 are etched and removed is shown, but this is not limited to this, and for example, etched grooves are formed on both sides of the mesa stripe 10, and the etched grooves are formed on the outside. It may be of a structure in which the active layer 3 and the like remain.

(Effects of the Invention) As described above, according to the present invention, in a BH-LD having a mesa drive, a p-type substrate is used, a p-type cladding layer and p2!11. l The current blocking layer is in contact with one side of the mesa stripe, and a semiconductor layer with a small band gap is introduced on the p-type current blocking layer.V
B1-1-Ll) was obtained which had higher optical output, improved characteristics, and significantly improved concentrator reliability than C.

[Brief explanation of the drawing]

Figures 1 and 2 show B of the first and second embodiments of the present invention.
3 and 4 are schematic diagrams of the current block structure of BH-L i) according to the present invention and the conventional example. Figure 5 is a cross-sectional view of the BH-LD according to the conventional example. A structural diagram is shown. In the figure, 1 p-InP substrate, 2 p-InP
3 is an active layer, 4 is an n-1nP cladding layer, and 5 is a n-InP current blocking layer. 61 dp-1nP current blocking layer, 7 n-InP buried layer, 8 InGaAsP electrode layer, 10 mesa stripe, 11 InGaAsP layer, 12 idp-InP cap layer, respectively. Agent Patent Attorney Uchihara 9' - Shiro・・・：

Claims (1)

[Claims] Forming mesa stripes on at least each of the cladding layers and the active layer of a multilayer structure semiconductor wafer in which a semiconductor multilayer film including an active layer sandwiched between at least p-type and n-type cladding layers is laminated on a semiconductor substrate. However, in a semiconductor laser having a buried heterostructure formed by growing this mesa stripe in a buried manner, an n-type current blocking layer and a p-type current blocking layer in contact with the p-type cladding layer on the side surface of the mesa stripe, except for the mesa stripe region, are provided. A semiconductor laser comprising: a current blocking layer; and a semiconductor layer having a smaller bandgap than the current blocking layer formed on the p-type current blocking layer.