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 np+‐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.

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AppL Phys. Lett. 56 (2), B January 1990



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