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

Heavy impurity doping has a strong effect on the np product, or n²_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 n² _ieD_n up to N_A≈10 ¹⁹ cm^-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_A≈10²⁰ cm^-3. The new measurements confirm the diode-based data below 10¹⁹ cm^-3 but show that its extrapolation above 10¹⁹ cm ^-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