Spectroscopy of impurity levels by measuring the microplasma turn on probabilities in GaP/Zn,O/diodes

The modifying effects of the avalanche breakdown on the space charge density of the depletion layer of GaP/Zn,O/p-n junctions have been studied by the double square pulsed method. The thermal-emission time constant of the impurity levels may be determined from measurements of the microplasma turn-on probability vs the time interval between the two pulses. By making these measurements at various temperatures, one can find the activation energy and also the thermal-capture cross-section of the impurity levels. The analysis of the breakdown-voltage variation with time and temperature permits one to draw conclusions about the type of the individual levels (minority or majority-carrier trap) and also about the impurity impact ionization. Five impurity centers were identified in the temperature interval 77–140°K; among them two centers which might be responsible for the anomalous short minority carrier lifetime, i.e., the low quantum efficiency of the red GaP lamps.