Impurities in High-Purity Germanium as Determined by Fourier Transform Spectroscopy

Fourier Transform Spectroscopy in the wave number range between 0 and 125/cm1 (0 to 15 meV) was used to determine the impurities producing shallow energy levels in high-purity germanium. The sensitivity of the method is sufficient to detect impurities at a concentration of 109/cm3 with excellent signal to noise ratio and the selectivity (energy resolution) allows a clean separation of all shallow levels. So far only net-concentrations can be observed so that it was necessary to measure n- and p-type material separately. The elements boron, gallium and indium appear to follow the expected segregation laws, while aluminum seems to be homogeneously distributed in the whole crystal. It has proven difficult to investigate n-type material due to the inability to produce low-noise electron-injecting contacts at the measuring temperatures (6 to 11°K).