Staas & Halsey
Semiconductor device
 A semiconductor device comprises an n-type emitter layer, a p-type base layer formed in contact with the n-type emitter layer, a first collector layer formed in contact with the base layer, and having a bandgap substantially equal to that of the p-type base layer, and a second collector layer formed in contact with the first collector layer, and having a bandgap wider than that of the first collector layer, the first collector layer having such a thickness that kinetic energy of electrons injected from the p-type base layer and flowing in the first collector layer is substantially 1.0 to 1.5 times the bandgap of the first collector layer at an interface between the first collector layer and the second collector layer. Electrons injected into the base layer can flow at very high speed in the first collector layer, because the first collector layer has a narrow bandgap. In addition, the avalanche breakdown never takes place in the first collector layer, because kinetic energy of the electrons is lower than substantially 1.0 to 1.5 times the bandgap of the first collector layer. 
Fujitsu Limited
H
H01L
inventional
Hiroshi
Yamada