Recombination Parameters in Low-Resistivity Gamma-Irradiatedn-Type Germanium

Abstract

Detailed studies of recombination in $\ensuremath{\sim}0.2\ensuremath{-}\ensuremath{\Omega}$ cm As- and Sb-doped ${\mathrm{Co}}^{60}$ $\ensuremath{\gamma}$-irradiated Ge are reported. The principal experimental techniques used were measurement of the variation of minority-carrier lifetime with temperature (at low excess density) and with excess density (using temperature as a parameter). The temperature dependence of the electron capture probability ${c}_{n}$ was obtained for both dopant cases. The hole capture probability ${c}_{p}$ was found, in both cases, to be approximately independent of temperature over the range examined. For Sb-doped material at 323\ifmmode^\circ\else\textdegree\fi{}K, the recombination-center energy-level position (neglecting statistical weight) was found to be 0.361\ifmmode\pm\else\textpm\fi{}0.005 eV above the valence band, with a possible slight temperature dependence corresponding roughly to one-half the variation of the band gap with temperature. The capture-probability ratio $\frac{{c}_{p}}{{c}_{n}}$ at this same temperature was 740. For the As-doped case, two different levels appear to dominate the recombination process in annealed and unannealed low-resistivity material. The energy-level positions relative to the valence band (neglecting statistical weight) are 0.327\ifmmode\pm\else\textpm\fi{}0.005 and 0.37\ifmmode\pm\else\textpm\fi{}0.01 eV at room temperature for the annealed and unannealed samples, respectively. The corresponding capture-probability ratios are 650 and 810. As in the case of Sb doping, the energy level appears to shift with temperature at about one-half the rate of the shift in band-gap energy.