Recombination Centers in Gamma-Irradiated Arsenic-Doped Germanium

A comprehensive investigation has been performed of the properties of recombination centers introduced in As-doped Ge by Co60 gamma rays. Materials of three resistivities were used: ~0.2, ~1 and ~8 Ω-cm. Measurements of lifetime versus temperature were made at low excess densities following various anneals. Numerous measurements of lifetime as a function of excess density with temperature as a parameter and with different annealing histories were performed. The position of the recombination center was observed to shift slightly with anneal temperature from Ev + 0. 346 ±.005 eV for room temperature stable defects to 0. 322 ±0.003 eV for samples which have been annealed in the range of ~70°C to ~120°C. These values are based on excess density measurements and assume unity statistical weight. The possible error from this assumption is estimated to be ±0.02 eV. The variation of electron capture probability with temperature was indicated by comparison with temperature dependence data; it varies approximately as T3/4. The hole-to-electron capture probability ratio near room temperature is 400 ±30 %. The arsenic atom appears to play no significant role in the process of recombination center creation or annihilation.