JPS6320036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical semiconductor light emitting device that generates a rapidly repeating ultrashort optical pulse train.

It is known that when a small non-emitting region exists within the resonator of a semiconductor laser, a phenomenon called self-pulsation SP occurs, and the optical output becomes pulsed even during DC operation. The laser power drops to near zero with each pulse. Self-pulsation SP is harmful in applications such as optical communications, but because the output is a narrow pulse of less than a nanosecond, it can be applied to excitation light sources for determining optical physical properties. Non-emissive regions that cause self-pulsation SP are formed by dark lines, dark regions, and electron traps that occur as the laser element deteriorates, but these cannot be created intentionally. A tandem laser shown in FIG. 1 has a non-emitting region for the purpose of generating short optical pulses by self-pulsation SP or for use as an optical switch. This laser has a configuration in which two lasers that share a resonator are arranged side by side.

In the tandem laser, as is clear from Figure 1, the two sections A and B have independent currents I ₁ and I _{2 .}
In order to supply current, it is necessary to separate the electrode on one side, and two or more independent current supply sources are required.

The present invention eliminates the above disadvantages, provides a semiconductor laser that is extremely easy to manufacture, and generates a rapidly repeating ultrashort pulse train using a simple driving method. For this purpose, the laser structure is made into a pnpn structure,
The breakdown that occurs at the np junction among the three junctions occurs distributed in the direction of the cavity, and by spatially distributing the current injected into the active layer, a light-emitting region and a non-light-emitting region are formed within the cavity. It is something.

Examples of the present invention will be described in detail below. FIG. 2 shows a semiconductor light emitting device of the present invention. Figure 2a is a perspective view;
FIGS. 2b and 2c are XX' cross-sectional views of FIG. 2a.

In Figure 2a, an n-type GaAs substrate 1 is
Ga0.65Al0.35As layer 2 2μm, P type
Ga0.93Al0.07A ₅ layer 3 0.1μm, P type
A Ga0.65Al0.35As layer 4 with a thickness of 1.3 to 1.5 .mu.m and an n-type GaAs layer 5 for ohmic contact with a thickness of 1.3 to 1.5 .mu.m are sequentially formed by continuous liquid phase epitaxial method. Thereafter, Zn, which is a P-type impurity, is diffused into a stripe region having a width of approximately 15 μm in order to limit the oscillation region or current injection region within the plane of the active layer. However, unlike a normal laser, the Zn diffusion front 7 is stopped in the middle of the n-type GaAs layer 5. In FIG. 2b, the distance between the Zn diffusion front 7 and the P-type Ga0.65Al0.35As layer 4 (P-clad layer) is changed periodically over the cavity length. The depth of Zn diffusion can be changed by changing the depth of Zn diffusion.
After etching the upper surface of the GaAs layer 5 (cap layer) at right angles to the current injection stripes with a period equivalent to W ₁ and a width equivalent to W ₂ , Zn is etched.
It would be better to spread it. W ₁ = 10 μm, W ₂ = 5 μm,
What is necessary is just to set _d1 =0.1-0.2 micrometer, and _d2 =0.2-0.3 micrometer. Figure 2c is an example in which the Zn concentration is changed periodically. Changing the concentration of the Zn diffusion layer in this way is
An oxide film is formed in advance on the top surface of the GaAs layer 5 (cap layer) at right angles to the current injection stripe with a period corresponding to W ₂ and a width equivalent to W ₂ , and the oxide film on the W ₂ portion is removed to perform the first Zn diffusion. Then, the oxide film on the stripe is removed, and a second Zn diffusion is performed over the entire surface of the stripe. The concentration of the front portion of Zn diffusion layer 6a is 5×10 ¹⁹ /cm ³ , and the concentration of the front portion of Zn diffusion layer 6b is 10 ¹⁷ /cm ³ . In addition, Fig. 2 b,
In c, an example was shown in which the Zn diffusion layer was changed periodically.
It may be changed non-periodically. 3 to 5 show the operating characteristics of the semiconductor light emitting device of the present invention. FIG. 3 shows the optical output versus current characteristics. The area indicated by the broken line c is an unstable region where the optical output increases rapidly with a slight increase in current. Figure 4 shows the current I as the oscillation threshold current.
The time waveform of the optical output when set slightly above Ith, that is, I=104 mA, is shown. Period T≒
2.5ns, pulse width △t~300ps, peak output approximately 15m
A W optical pulse train is obtained. FIG. 5 shows the change in pulse repetition frequency when the current is changed. By changing the current
The frequency changes repeatedly from 200MHz to 1GHz.

The above-mentioned operating characteristics can be explained as follows. When Zn is diffused non-uniformly over the cavity length as shown in Figure 2c, the n-type GaAs layer 5 and the p-type
The breakdown of the reverse bias junction of the Ga0.65Al0.35A ₅ layer 4 occurs non-uniformly according to the Zn diffusion profile. Breakdown voltage is n-type GaAs layer 5
Since it is very narrow, about 0.1 μm, it occurs with a reverse voltage of about 2V. Spatial non-uniform breakdown results in non-uniform injection current into the active layer 3. Therefore, a gain region and a loss region are generated over the length of the resonator, and the conditions for the generation of self-pulsation SP are established. The ratio of the light-emitting region (gain region) to the non-light-emitting region (loss region) and the ratio of the respective gain coefficients and loss coefficients can be easily changed by changing the diffusion profile.

As is clear from the above description, considering the planar stripe structure, the semiconductor light emitting device of the present invention can be manufactured in almost the same manufacturing process as the conventional semiconductor light emitting device. Moreover, the operating method and operating means are simple. Ultrashort optical pulses with subnanosecond width and peak power of 10 mW can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a conventional tandem laser, Fig. 2 is a perspective view and cross-sectional view of a semiconductor light emitting device of the present invention, Fig. 3 is optical output vs. current characteristics, and Fig. 4 is a temporal waveform of optical output ( FIG. 5 is a diagram showing pulse repetition frequency versus current characteristics. 1: GaAs substrate, 2: N-clad layer, 3: Active layer, 4: P-clad layer, 5: Cap layer, 6:
Zn diffusion layer, 8: n-type electrode, 9: p-type electrode.

Claims (1)

[Claims] 1. On a compound semiconductor substrate 1 of one conductivity type, a compound semiconductor cladding layer 2 of one conductivity type, a conductive compound semiconductor active layer 3, a compound semiconductor cladding layer 4 of opposite conductivity type, and a compound semiconductor cladding layer 4 of one conductivity type. A compound semiconductor cap layer 5 is sequentially formed, and is formed by diffusion of an impurity imparting reverse conductivity from the surface of the compound semiconductor cap layer 5 of the one conductivity type, and a front 7 of the impurity diffusion is formed in the surface of the compound semiconductor cap layer 5 of the one conductivity type. It is stopped in the middle of the compound semiconductor cap layer 5 and limits the oscillation region within the plane of the active layer 3.
It is a pnpn structure semiconductor laser including a forward p-n junction constituting a light emitting region provided with a stripe region 6 of opposite conductivity type, and the front 7 of the impurity diffusion of the stripe region 6 of opposite conductivity type and the front 7 of the impurity diffusion of the stripe region 6 of opposite conductivity type are connected to each other. The distance of the cladding layer 4 is changed periodically or aperiodically at right angles to the current injection stripe over the cavity length, or the impurity concentration of the stripe region 6 of the opposite conductivity type is changed over the cavity length. By changing the current injection stripe periodically or non-periodically at right angles to the current injection stripe, the current injection stripe is distributed either periodically or non-periodically in parallel to the forward p-n junction and in the cavity length direction of the semiconductor laser. A semiconductor light emitting device characterized by providing a non-uniform reverse bias junction.