Effects of heavy impurity doping on the np product in p-GaAs

Abstract

Heavy impurity doping has a strong effect on the np product, or n/sup 2//sub ie/, in p-GaAs. The authors' initial work made use of a successive etch technique to extract the electron injection current, in p-n diodes and to measure n/sup 2//sub ie/D/sub n/ up to N/sub A/ approximately=10/sup 19/ cm/sup -3/. The authors have used a new approach, analysis of the collector current in n-p-n homojunction bipolar transistors. Because this approach isolates the current of interest, it offered increased accuracy and allowed the extension of the measurements to N/sub A/ approximately=10/sup 20/ cm/sup -3/. The new measurements confirm the diode-based data below 10/sup 19/ cm/sup -3/ but show that its extrapolation above 10/sup 19/ cm/sup -3/ would yield incorrect results. The authors' previous work on the implications of effective bandgap shrinkage for GaAs-based solar cells is reassessed in light of the more recent data.<>