Photothermal ionization spectroscopy of acceptors in high purity germanium

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Abstract
The results obtained by photothermal ionization spectroscopy on acceptors in high-purity germanium are presented. The distribution of the residual acceptor impurities, boron and aluminum, in high-purity germanium crystals are studied by lightly doping the crystals with gallium, and using semiconductor statistics to determine the relative concentrations of the shallow acceptors from their relative peak heights in the spectra. Under the conditions of growth (SiO2 crucible, H2(g) ambient) the distributions of aluminum and boron do not follow the equation for normal segregation The distribution profiles of aluminum indicate that it is being removed from the melt during growth while the distribution profiles of boron are usually consistent with boron being added to the melt during growth. Data were taken with a high resolution (0.10 cm−1) Fourier transform spectrometer. Transition energies are tabulated for the acceptors observed. Three new shallow acceptors are reported. Two have D transitions at 60.20 and 64.69 cm−1, respectively. The other acceptor has a split ground state with D transitions at 69.12 and 73.77 cm−1. The deepest acceptor observed was neutral copper with a binding energy measured to be 348.9 cm−1 (43.27 meV).