Light emitting semiconductor diode

DETAILED DESCRIPTION As is shown in FIG.
1, two semiconductor layers 39, 40 are formed on a semiconductor substrate 43 using conventional semiconductor technology.
The first layer 39, of n conductivity type GaAs doped with Te about 1 .
mu.
m thick, has a high impurity concentration (5.
times.
10.
sup.
18 cm.
sup.
-.
sup.
3) and a narrow forbidden band gap.
The second layer 40, of Ga.
sub.
0.
7 Al.
sub.
0.
3 As doped with Sn about 2 .
mu.
m thick, has an impurity concentration (1.
times.
10.
sup.
18 cm.
sup.
-.
sup.
3) lower than that of the first layer 39.
The substrate 43 of Ga.
sub.
1-x Al.
sub.
x As (x.
ltoreq.
0.
3) doped with Zn about 150 .
mu.
m thick has an impurity concentration of 1.
times.
10.
sup.
18 cm.
sup.
-.
sup.
3.
The second and third layers form a p-n junction 41 therebetween.
The first layer 39 has a high impurity concentration and a narrow forbidden band so that the metal electrodes disposed thereon can form good ohmic contact with the first layer.
On the other hand, the second layer 40 has a low impurity concentration so that a high internal quantum efficiency can be obtained.
The substrate has a crystal composition ratio x giving a forbidden band gap determined by the wavelength of the light to be obtained near the p-n junction 41.
The crystal composition ratio increases with increasing distance from the p-n junction.
Ring-shaped portions of layers 39 and 40 are transformed into p conductivity type by selectively diffusing zinc so as to form a high impurity concentration p conductivity type layer 38 about 5 .
mu.
m thick, as illustrated in FIG.
2.
The remaining parts of the first and second layers having a diameter of about 160 .
mu.
m form the first and second semiconductor regions 46 and 42, respectively.
A phosphosilicate glass film 51 having a thickness of between 4000 and 6000 A is desposited on the first region 46 and the high impurity concentration p conductivity type layer 38.
A number of perforations are formed in the central part of the phosphosilicate glass film 51 on the first region 46 by well-known photolithographic techniques