Semiconductor device

Claim 2

A semiconductor device comprising: an emitter layer having a first conductivity type and a first energy band gap and a second energy band gap greater than the first energy band gap; a base layer having a predetermined conductivity type, provided on the emitter layer, and having a third energy band gap less than said first band gap of the emitter layer defining a heterojunction surface between the emitter layer and the base layer so that there is a discontinuity between conduction band edges of the emitter layer and the base layer so as to form an energy barrier therebetween so that hot electrons can be injected into said base layer from said emitter layer; one of comb-shaped and lattice-shaped base electrodes, formed adjacent to the heterojunction surface; and a collector layer having the first conductivity type, provided on the base layer.

Claim 3

A semiconductor device according to claim 1, further comprising: an emitter contact layer formed on said emitter layer opposite to said base layer, wherein the band gap of said emitter layer gradually increases from the emitter contact layer to the base layer.

Claim 4

A semiconductor device according to claim 1, wherein the order of the position of the emitter layer, the base layer, and the collector layer is reversed.

Claim 5

A semiconductor device according to claim 1, wherein Schottky junctions are formed between said electrodes and said base layer, and between said electrodes and said emitter layer.

Claim 6

A semiconductor device according to claim 1, further comprising an insulator layer formed between said electrodes and said base layer and said emitter layer.

Claim 7

A semiconductor device according to claim 1, wherein said electrodes are formed so as to not ohmicly contact the base layers and the emitter layer.

Claim 8

A semiconductor device comprising: a first emitter layer having a first conductivity type and comprising a first compound semiconductor; ax second emitter layer having first and second surfaces, the first surface formed on the first emitter layer and having the first conductivity type, the second emitter layer comprising a second compound semiconductor and having a first energy band gap at the first surface and a second energy band gap at the second surface being larger than the first energy band gap; a base layer formed on the second surface of said second emitter layer having the first conductivity type, a band gap less than the first band gap so that hot electrons can be injected into said base layer from said second emitter layer and comprising the first compound semiconductor; electrodes comprising one of comb-shaped and lattice-shaped electrodes, formed in the base layer; and a collector layer formed on the base layer, having the first conductivity type and comprising the first compound semiconductor.

Claim 9

A semiconductor device comprising: a first emitter layer having a first conductivity type and comprising a first compound semiconductor; ax second emitter layer having first and second surfaces, the first surface formed on the first emitter layer and having the first conductivity type, the second emitter layer comprising a second compound semiconductor and having a first energy band gap at the first surface and a second energy band gap at the second surface being larger than the first energy band gap; a base layer formed on the second surface of said second emitter layer having the first conductivity type, a band gap less than the first band gap so that hot electrons can be injected into said base layer from said second emitter layer and comprising the first compound semiconductor; electrodes comprising one of comb-shaped and lattice-shaped electrodes, formed in the base layer; and a collector layer formed on the base layer, having the first conductivity type and comprising the first compound semiconductor.

Claim 10

A semiconductor device according to claim 7, wherein the first compound semiconductor comprises GaAs and the second compound semiconductor comprises Al x Ga 1-x As, where 0≦x≦1.

Claim 11

A semiconductor device according to claim 7, wherein the first compound semiconductor comprises In y Ga 1-y As, where 0≦y≦1, and the second compound semiconductor consists of one of In p and Al z In 1-z As, where 0≦z≦1.

Claim 12

A semiconductor device according to claim 7, wherein a band gap of said second emitter layer gradually increases from the junction between the first emitter layer and the second emitter layer, at which the energy level is approximately equal to an energy level of a conduction band edge of the first emitter layer, to the junction between said second emitter layer and said base layer.