Abstract
Diffused junctions prepared from GaP grown by the rotating floating‐zone technique exhibit microplasma breakdown and accompanying light emission at 298°K at defects due to dislocations and a precipitated second phase. At 77°K this mechanism does not occur in the same bias range. Instead, at higher reverse bias, breakdown and light emission occurs from many spots which form a gross spiral pattern when the junction plane is normal to the growth axis. The breakdown regions correspond to local fluctuations in impurity concentrations produced during growth, these fluctuations being introduced at one point during each rotation of the floating‐zone ingot. The shape of the solid‐liquid interface during growth agrees well with that predicted from the dimensions of the spiral pattern and the growth parameters.