Electrical measurements of bandgap shrinkage in heavily dopedp-type GaAs

Electron currents injected intop ⁺ -GaAs were measured by analyzing the collector current versus base-emitter voltage characteristics ofn-p ⁺ -n GaAs homojunction transistors. This technique facilitates accurate determination of electron injection currents forp-type GaAs doped greater than 10²⁰ cm⁻³. Previous experiments used a diode-based, sequential etch technique to demonstrate that so-called bandgap shrinkage effects substantially increase the electron current injected into p⁺-GaAs. However, the diode-based technique was limited to dopant concentrations ≤10¹⁹ cm⁻³. Using the homojunction transistor-based technique described in this paper, we report a similar enhancement of the electron current injected intop-type GaAs doped as heavily as 8 × 10¹⁹ cm⁻³.