SEMICONDUCTOR MATERIAL FOR ELECTRONIC DEVICE AND SEMICONDUCTOR ELEMENT USING SAME

摘要

An epitaxial substrate having a bipolar transistor structure comprises a collector layer (3), a base layer (4) and an emitter layer (5) on a GaAs substrate (2). The base layer (4) is composed of a lower base layer (41) and an upper base layer (42) having a desired carrier concentration, and a low carrier-concentration layer (43) having a low carrier concentration. The low carrier-concentration layer (43) is formed between the lower base layer (41) and the upper base layer (42), and has a function of ballast. Either of the lower base layer (41) and the upper base layer (42) may be omitted. Electrons pass through the low carrier-concentration layer (43) more easily as the temperature increases, so that the low carrier-concentration layer (43) functions to increase the amplification factor. Consequently, the transistor characteristics can be thermally stabilized.