Heterojunction bipolar transistor with inversion layer base

Claim 1

A bipolar semiconductor device comprising: a first semiconductor region of a first conductivity type; a second semiconductor region having two opposing surfaces and having between said two opposing surfaces a thickness sufficient to suppress carrier tunneling through said second semiconductor region and for majority carriers to be transported through a conduction band of said second semiconductor region which contacts at one of said two opposing surfaces the first semiconductor region, has a bandgap wider than that of the first semiconductor region and forms an energy barrier with respect to minority carriers of the first semiconductor region; a conductive region in contact with the other surface of the second semiconductor region at said other surface to form a barrier height less than 0.5 eV with respect to majority carriers of the first semiconductor region; and an electrically induced layer with conductivity type opposite to the first conductivity type formed in the operating state in a surface portion of the first semiconductor region in contact with the second semiconductor region on which the conductive region contacts, wherein carriers supplied from the conductive region and transported through a conduction band of the second semiconductor region reach the first semiconductor region across the electrically induced layer to cause the conductive region to act as an emitter, the electrically induced layer to act as a base and the first semiconductor region to act as a collector of a transistor.