JPS6019158B2 - semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting device such as a semiconductor laser, which modulates generated light and is suitable for use in optical communication.

The relationship between current 1 and optical output L in a typical semiconductor laser is as shown in characteristic line A in FIG. In the figure,
The sudden rise of characteristic line A at the point of current 1 indicates that this is a threshold and oscillation has started. As is clear from the figure, the semiconductor laser has already emitted spontaneous emission light L before starting oscillation. If, for example, pulse modulation is to be applied to the actual optical output of such a semiconductor laser, if the modulation signal Ms is applied with a bias up to the threshold point, the optical output Wut will be obtained as shown in the figure.
By the way, since this optical output LoM includes a component of spontaneous emission light L, it is not possible to have a large on/off ratio, the resistance to noise is low, and malfunctions are likely to occur.

The present invention reduces spontaneous emission light to almost zero at threshold current,
This makes it possible to obtain a semiconductor light emitting device with a high light on/off ratio, and this will be explained in detail below.

FIG. 2 is a side sectional view of a main part of an embodiment of the present invention.

In the figure, 1 is the substrate, 2 is the cladding layer, 3 is the active layer,
4 is a clad layer, 5 is a cap layer, 6 and 7 are metal electrodes,
8 each indicate a saturable absorption layer.

The most distinctive feature of this embodiment is that a saturable absorption layer 8 is formed on at least one of the open surfaces of the semiconductor laser from which light is to be emitted.

In this way, all the light output before the function value can be absorbed by the saturable absorption layer 8, and the spontaneous emission light L, shown in FIG. 1, can be made almost to a value close to zero, and, When the semiconductor laser starts oscillating and the optical power rises, the light absorption by the absorption layer 8 is saturated, so that light is emitted to the outside.
Therefore, part 1. The L characteristic is the characteristic line B seen in Figure 1.
As shown, the light on/off ratio becomes extremely good.
The operation that malfunctions due to the presence of noise is eliminated. By the way, colored glass can be used as the material for the saturable absorption layer 8, and it can be processed by sputtering, CVD (Chemical
It may be formed into a film by applying the vapor deposition method. In addition, it is also possible to use a semiconductor material that absorbs light other than colored glass, but if this is used, the external efficiency after oscillation, that is, the ratio of the amount of light that can be emitted to the outside to the amount of internally generated light, will be slightly smaller. Become. In addition, if forming the saturable absorbent layer 8 directly on the hair surface causes problems, for example, as shown in FIG. It may also be configured as a sandwich.

In this case, considering the respective thicknesses of the silicon dioxide layer 9 and the steelable absorption layer 8, these layers are equivalently the same as when they are not formed. Since the curvature of o increases the skin reflectance, it is also effective in reducing the threshold current.

In this configuration, when a semiconductor material is used as the saturable absorption layer 8, if a level is created within the band of the semiconductor, the semiconductor material is selected so that the optical energy of a predetermined wavelength is between the levels, This allows saturable absorption of light to occur depending on whether the level is filled with carriers excited by light irradiation. Since a semiconductor has a higher refractive index than silicon dioxide, the structure shown in FIG. 3 can have an extremely high reflectance, theoretically reaching 100%. It goes without saying that the higher the reflectance, the lower the dark value current. Note that, for example, in the case of only a saturable absorption layer made of a gallium abrasive (DaAs) layer, the light reflectance is 30%.
That's about it. As can be seen from the above explanation, according to the present invention, a saturable light absorbing layer is formed on at least one of the male surface, which is the light emitting surface of the semiconductor laser. Spontaneous emission light can be reduced to almost zero, the on/off ratio of emitted light can be increased, and high-quality optical communication that is less susceptible to noise and the like becomes possible.

In addition, by forming a saturable absorbing layer or sandwiching the layer with layers of materials with a lower refractive index, the light reflectance at the male surface is improved and the threshold current is reduced. It is possible to improve its characteristics such as increasing the temperature of the battery, and furthermore, it is possible to extend its life.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the 1·L characteristics of a semiconductor laser;
The figure is a side sectional view of the main part of an embodiment of the present invention, and FIG. 3 is a side sectional view of the main part of another embodiment. In the figure, 1 is the substrate, 2 is the cladding layer, 3 is the active layer,
4 is a cladding layer, 5 is a cap layer, 6 and 7 are electrodes, and 8 is a saturable absorption layer. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A semiconductor light-emitting device comprising a light saturable absorption layer formed on at least one light-emitting surface to absorb spontaneously emitted light generated before the start of laser oscillation.