Patent ID: 7242038

Claim:
A heterostructure bipolar transistor, comprising: a substrate made of InP; a collector layer formed on said substrate and made of a compound semiconductor containing indium and phosphorus; a base layer formed on said collector layer and made of a p-type compound semiconductor containing gallium, arsenic, and antimony, said base layer containing carbon added as a dopant; an emitter layer formed on said base layer and made of a n-type compound semiconductor containing indium, aluminum and phosphorus; wherein at least one GaAs (x) Sb (1-x) layer is used in said base layer and at least one In (1-y) Al (y) P layer is used in said emitter layer, where x and y represent an As content and an Al content, respectively, in a mixed crystal composition; wherein said As content x is in the range of 0.45≦x≦0.55 and said Al content y is in the range of 0<y≦0.25, with x and y satisfying the formula 0.49x+1.554y>0.36; wherein a composition ratio of indium to aluminum in said emitter layer is in a range within which a potential energy in a conduction band edge of said emitter layer close to said base layer side is higher than that in a conduction band edge of said base layer.