JPS62221179A - Embedded semiconductor laser - Google Patents

Abstract

PURPOSE:To contrive not to increase the leakage current even at the time of injection of a high current and to attain a high optical output and a high efficiency in the titled semiconductor laser by a method wherein the laser is composed of a semiconductor substrate, a first buried layer which has a conductivity type opposite to that of the semiconductor substrate and a band gap energy smaller than that of a second buried layer, a second buried layer having a conductivity type opposite to that of the semiconductor substrate, and a third buried layer having the same conductivity type as that of the semiconductor substrate. CONSTITUTION:This semiconductor laser is constituted of a p-type InP substrate 1, an InGaAsP active layer 2, an n-type InP clad layer 3, an insulating film 6 and electrodes 7 and 8; and an n-type InGaAsP first buried layer 11, which is a semiconductor layer having the opposite conductivity type to the conductivity type of the substrate 1 and has a band gap energy smaller than that of an n-type InP second buried layer 12, is interposed between the substrate 1 and the second buried layer 12. A hetero transistor of a p-n-n-P structure is composed of the substrate 1, the buried layers 11 and 12 and a p-type InP third buried layer 13 and the gain is very small. Accordingly, the leakage current can be very lessened even at the time of injection of a high current and a large optical output can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a buried semiconductor laser mainly used as a light source for optical communications.

"Prior Art" In recent years, various buried semiconductor lasers have been developed and put into practical use because they have the advantage of stably performing laser oscillation in a single transverse mode. FIG. 3 is a cross-sectional view showing an example of this type of semiconductor laser, and in this figure, l is p-
rnP substrate, 2 is InGaAsP active layer, 3 is n-1n
P cladding layer, 4 n-InP first buried layer, 5 p-r
The nP second buried layer, 6 is an insulating film, and 7 and 8 are electrodes.

"Problems to be Solved by the Invention" In the conventional buried semiconductor laser described above, as is clear from the figure, the substrate 1 and the first . Second buried layer 4.5
constitutes a p-n-p transistor, and its energy band diagram is as shown in Fig. 4 (a) without bias, and when positive and negative bias voltages are applied to electrodes 8 and 7, respectively When the voltage is applied, the result will be as shown in FIG. 4 (b). In the figure, F indicates the Fermi level and Eg indicates the energy gap.

By the way, when the substrate l and the buried layers 4 and 5 have a transistor structure, the leakage current passing through the buried layers 4 and 5 becomes the base current of the transistor, and as a result, if the leakage current increases beyond a certain level, A large current flows through the buried layers 4 and 5 (the transistors are turned on). Therefore, in conventional buried semiconductor lasers, there has been a problem in that the leakage current passing through the buried layers 4 and 5 increases, especially when the injection current is high, and this reduces optical output and efficiency. . The solid line L1 in FIG. 5 indicates the injection current vs. optical output characteristic of the conventional buried semiconductor laser. As is clear from this figure, as the injection current increases, the slope of the characteristic curve of the conventional laser increases. It gradually becomes smaller and eventually the light output becomes saturated.

This invention has been made in view of the above-mentioned circumstances, and its purpose is to provide an embedded type that can achieve high optical output and high efficiency without increasing leakage current even when a high injection current is applied. The purpose of the present invention is to provide semiconductor lasers.

``Means for Solving the Problems'' This invention provides a buried method in which both sides of a striped active layer formed on a semiconductor substrate are buried with a plurality of buried layers sequentially stacked on the semiconductor substrate. type semiconductor laser, the multiple buried layers are of the opposite conductivity type to the semiconductor substrate.
and a first buried layer having smaller reband gap energy than the second buried layer, and a second buried layer having a conductivity type opposite to that of the semiconductor substrate.
It is characterized in that it is composed of a semiconductor substrate and a third buried layer of the same conductivity type.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing the structure of an embodiment of the present invention. In this figure, l is a p-InP substrate, 2 is [
The nGaAsP active layer, 3 an n-1nP cladding layer, 6 an insulating film, and 7.8 electrodes, these structures are the same as those shown in FIG.

Further, 12 is an n-InP second buried layer, and 13 is a p-1nP layer.
This is the third buried layer, and is the same as the buried layer 4.5 in FIG. The semiconductor laser according to this embodiment is different from the semiconductor laser shown in FIG. That is, in this embodiment, an n-InGaAsP first buried layer 11 is interposed.

In this example, the substrate! and the buried layer If~13 constitute a p-n-n-pi heterotransistor, and its energy band diagram is as shown in FIG. 2 (a) in the case of no bias, and , when positive and negative bias voltages are applied to the electrodes 8 and 7, respectively, as shown in FIG. 2 (b). By the way, at the time of bias, the buried layers 11 to
The leakage current passing through 13 is as shown in Figure 2 (b).
The holes are injected from the substrate l into the first buried layer 11.

However, in this embodiment, the bandgap energy of the first buried layer 11 is smaller than the bandgap energy of the second buried layer 12, resulting in an energy barrier (
A heterobarrier (2) is formed, and this energy barrier prevents holes from diffusing into the second buried layer 12. That is, according to this embodiment, the substrate 1 and the buried layer 11-
The gain of the transistor formed by the transistor 13 is extremely small, so even when a high current is injected, the leakage current can be made extremely small, thereby making it possible to obtain a large optical output. The optical output characteristics of this example are shown in FIG. 5 by a broken line L2.

Note that the bandgap wavelength λ9 of the first buried layer 11 is 1.0 to 1.25 μm when λ9 of the active layer 2 is 1.3 μm.
When λ9 of the active layer 2 is 1.5 to 1.6 μm, a suitable value is about 1.1 to 1.35 μm. Moreover, p (or n) -I nGaAsP is added on the third buried layer I3 to avoid thermal damage and to increase flatness.
The layers may be laminated.

Further, although the above embodiment uses a p-type substrate l, the present invention is also applicable to a semiconductor laser using an n-type substrate. In this case, the conductivity types of the buried layers 11-13 are reversed. Further, the present invention is applicable to GaAs-based semiconductor lasers. Further, the present invention provides a Fabry-Perot type laser,
It is applicable to various semiconductor lasers such as distributed feedback lasers and distributed reflection lasers.

"Effects of the Invention" As explained above, according to the present invention, leakage current can be made extremely small even when a high injection current is applied. This makes it possible to obtain a semiconductor laser with high optical output and high efficiency, which is extremely useful as a light source for long-distance communications. Furthermore, since the semiconductor laser according to the present invention can obtain high output, even if the coupling efficiency with the optical fiber is poor, the output at the end of the optical fiber can be increased, and as a result, coupling with the optical fiber becomes easy. , the span length between repeaters can be made longer. Furthermore, when aging is performed with a constant light output, the higher efficiency allows driving with lower current, improving temperature characteristics and reliability.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of the present invention, and FIG.
Figures (A) and (B) are energy band diagrams of the same embodiment in non-biased and biased states, respectively. Figure 3 is a cross-sectional view showing an example of the configuration of a conventional buried semiconductor laser. Figure 4 (A). ,(
b) are energy band diagrams of the same semiconductor laser in non-biased and biased states, and FIG. 5 is a diagram showing the Kerr injection current characteristics of the semiconductor lasers shown in FIGS. 1 and 3. l... Semiconductor substrate, 2... Active layer, 1
1 Mountain: first buried layer, 12: second buried layer, 13: third buried layer

Claims (1)

[Claims] A buried semiconductor laser in which both sides of a striped active layer formed on a semiconductor substrate are buried by a plurality of buried layers sequentially stacked on the semiconductor substrate,
The plurality of buried layers are of a conductivity type opposite to that of the semiconductor substrate.
and a first buried layer having smaller reband gap energy than the second buried layer, a second buried layer having a conductivity type opposite to that of the semiconductor substrate, and a third buried layer having the same conductivity type as the semiconductor substrate. An embedded semiconductor laser.