Transistor-based measurements of electron injection currents in p-type GaAs doped 1018–1020 cm−3

Abstract

Measurements of electron currents injected into p+-GaAs are presented for molecular beam epitaxially grown material doped from 2×1018 to 8×1019 cm−3 with Be. The collector current versus base-emitter voltage characteristics of n-p+-n GaAs homojunction bipolar transistors are analyzed, and the results are interpreted in terms of the quantity (n0Dn), where n0 is the equilibrium minority-carrier concentration and Dn is the minority-carrier diffusion coefficient. The results are consistent with earlier measurements of (n0Dn) made using metalorganic chemical vapor deposited p+-n GaAs solar cells, Zn doped as heavily as 1×1019 cm−3. The large electron injection currents observed are interpreted as evidence for significant effective band-gap shrinkage. These effects must be accounted for in the modeling and design of GaAs-based heterojunction bipolar transistors and solar cells.