JPH0377677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-efficiency semiconductor laser whose threshold current changes little with respect to changes in environmental temperature and whose output level fluctuates little.

High-efficiency semiconductor lasers, which have excellent environmental resistance and whose output level does not fluctuate even when the temperature changes, are desirable as light sources for optical fiber communications, and they can also be operated by integrating semiconductor lasers and electronic elements. Even when heat is generated, the fact that the laser output fluctuates less significantly improves the reliability of the entire device.

As a method of reducing output fluctuations due to temperature changes, a laser structure in which the active layer thickness is reduced to about the de Broglie wavelength of the carrier has been proposed. Here, the de Broglie wavelength λd is a quantity defined by λd = h/p using Planck's constant h and the carrier momentum P. Accordingly, in GaAs, it is about λd ~ 300 Å, which is a small value compared to the carrier diffusion length. It is. In such a thin active layer, electrons and holes become two-dimensional electrons and holes whose motion in the thickness direction is quantized. FIG. 1 schematically shows a band diagram in a state where a forward bias voltage is applied to a semiconductor laser having a double heterostructure and a thin active layer having a thickness of quantum theoretical dimensions. In the same figure,
11 is an n-type semiconductor layer, 12 is an active semiconductor layer, 13
is a P-type semiconductor layer, and 141 and 142 are discrete conduction band energy levels that appear because the active layer has quantum theoretical dimensions. Further, 151 and 152 are discrete valence band energy levels that similarly appear in the valence band, and show a case where two energy levels are formed in the conduction band and two energy levels each in the valence band. The forbidden band widths of the n-type semiconductor layer 11 and the p-type semiconductor layer 13 are larger than the forbidden band width of the active semiconductor layer 12. Compared to a semiconductor laser in which the active layer thickness is slightly thicker than the de Broglie wavelength, in a semiconductor laser as shown in Fig. 1 where the active layer thickness is around the de Broglie wavelength or less, the carrier in the active layer is smaller than the layer thickness. For directional motion, only a small number of energy states are possible, as indicated by discrete energy levels. The fewer energy states a carrier can occupy, the more
As the number of carriers accumulated in individual energy states, especially those related to laser oscillation, fluctuates due to external temperature changes, the temperature dependence of the threshold current and optical output of the semiconductor laser shown in Figure 1 becomes smaller. .

However, since the active layer consists of only one layer and is thin, the carrier density is higher at the same current value than in the case of a normal thick layer, and electrons cross the heterobarrier into the P-type semiconductor layer 13, and holes pass through the n There is a drawback that the current component that leaks into the semiconductor layer 11 and is not related to light emission increases relatively, resulting in a decrease in efficiency.

The present invention eliminates these drawbacks and provides highly efficient,
The purpose of this is to realize a semiconductor laser with a small temperature change in threshold current. The semiconductor layer has a structure in which semiconductor layers having a large forbidden band width are alternately stacked, and side surfaces parallel to the propagation direction of light propagating through the active semiconductor layer are covered with the semiconductor layer having a larger forbidden band width than the active semiconductor layer. However, current is injected into the active semiconductor layer through this semiconductor layer.

This will be explained in detail below using the drawings.

FIG. 2 shows an embodiment of the present invention. In the figure, 21 is a semi-insulating GaAs substrate, 221,
222, 223, 224 and 225 are high resistance
AlxGa ₁ −xAs, 231, 232, 233 and 2
34 is GaAs and serves as an active semiconductor layer. 24 is n ⁺ type
AlyGa ₁ -yAs, 25 is P ⁺ type AlyGa ₁ -yAs, 26
is a p-type electrode, and 27 is an n-type electrode. However, 0
≦x≦1, 0≦y≦1. The axial direction of the resonator is perpendicular to the plane of the paper. Semi-insulating in manufacturing
High resistance is achieved by molecular beam growth on GaAs substrate 21.
AlxGa ₁ −xAs221 was grown to about 1 μm, and then
GaAs231, 232, 233 and 234 and high resistance _AlxGa1 -xAs222, 223 and 224 are grown alternately to a thickness of about 150 Å, and then high resistance
AlxGa ₁ -xAs225 is grown to about 1 μm. After that, n ⁺ type AlyGa ₁ −yAs24 and P ⁺ type AlyGa ₁ −yAs
Remove the part marked 25 by etching and place it there.
N ⁺ type AlyGa ₁ −yAs is grown in vapor phase, and Zn is selectively diffused only in the left part to form P ⁺ type AlyGa ₁ −yAs.
25, and finally electrodes 26 and 27. In this example, GaAs23 becomes the active semiconductor layer.
The layer thicknesses of layers 1, 232, 233 and 234 are approximately 1/2 of the de Broglie wavelength. The current flows from the electrode 26 to P ⁺ AlyGa ₁ −yAs 25 and GaAs 23
n ⁺ type through 1,232,233 and 234
AlyGa ₁ -yAs 24 flows to the electrode 27. high resistance
AlxGa ₁ −xAs221, 222, 223, 224
And the forbidden band width of 225 is GaAs231, 232,
It is larger than the forbidden band width of 233 and 234, and the band diagram in the layer thickness direction shown by the dashed line in FIG.
As shown in the figure, GaAs231, 232, 23
Discrete energy levels are generated in the conduction band and valence band of 3 and 234. However, the figure shows a case where two energy levels are generated in each of the conduction band and the valence band. The active semiconductor layer is n ⁺ Al ₁ −yGayAs24 and P ⁺ Al ₁ −yGayAs, which have a large forbidden band width in the direction parallel to the layer thickness where current is injected.
Since it has a double heterostructure sandwiched by 25, carriers are efficiently injected into the active semiconductor layer and oscillation occurs. n ⁺ Al ₁ −yGayAs24 and P ⁺ Al ₁ −
By injecting current laterally into the active semiconductor layer through yGayAs 25, carriers can be injected efficiently and uniformly. Even if you try to inject carriers by flowing a current vertically (= stacking direction) through multiple active semiconductor layers, it is difficult to inject carriers uniformly into each active semiconductor layer, and this method is difficult to inject carriers uniformly into each active semiconductor layer. It is difficult to sufficiently realize the characteristic of reducing the size. Therefore, performing current injection from the lateral direction is an essential component of the present invention. Furthermore, since a semiconductor laser with horizontal injection can have a planar structure, it is easier to integrate it with electronic devices compared to a semiconductor laser with vertical current injection. In a conventional semiconductor laser in which the active semiconductor layer is thin and consists of a single layer, and the active layer is thin as shown in the band diagram shown in Figure 1, as the injected current increases, a reactive current that does not contribute to light emission crosses the heterobarrier. However, according to this embodiment, the active semiconductor layer consists of four layers, so even with the same current value, the carrier density per active layer is reduced to 1/4. As a result, active semiconductor layers 231, 232, 233 and 234
The number of holes crossing the heterobarrier between n ⁺ Al ₁ −yGayAs 24 is reduced, and similarly the active semiconductor layer 231,
232, 233 and 234 and P ⁺ Al ₁ −yGayAs2
Since the number of electrons crossing the heterobarrier between 5 and 5 is reduced, current components that do not contribute to light emission can be reduced.

As described above with the specific examples, according to the present invention, a semiconductor laser with high efficiency and small temperature change in threshold current can be realized, and is particularly effective when a material with a small heterobarrier is used.

[Brief explanation of drawings]

Figure 1 is a band diagram of a conventional semiconductor laser, Figure 2 is a band diagram of a conventional semiconductor laser.
The figure shows one embodiment of the present invention, and FIG. 3 is a band diagram thereof. 11 is an n-type semiconductor layer, 12 is an active semiconductor layer, 1
3 is a P-type semiconductor layer, 141 and 142 are conduction band energy levels, 151 and 152 are valence band energy levels, 21 is a semi-insulating GaAs substrate, 22
1,222,223,224 and 225 are high resistance
AlxGa ₁ −xAs, 231, 232, 233 and 2
34 is GaAs, 24 is n ⁺ type AlyGa ₁ −yAs, 25 is
P ⁺ type AlyGa ₁ -yAs, 26 and 27 are electrodes.

Claims (1)

[Claims] 1. A multilayer structure in which active semiconductor layers having a thickness of approximately or less than the de Broglie wavelength of electrons and holes and semiconductor layers having a larger forbidden band width than the active semiconductor layer are laminated alternately, and The structure includes a structure in which a plane parallel to the propagation direction of light propagating in the active semiconductor layer is covered with a semiconductor layer having a larger forbidden band width than the active semiconductor layer, and the active semiconductor layer is passed through the semiconductor layer. 1. A semiconductor laser comprising means for injecting current into the semiconductor laser.