Photothermal ionization spectroscopy of donors in high-purity germanium

The results of narrow linewidth (0.10 cm−1 FWHM) photothermal ionization spectroscopy (PTIS) investigations of shallow donors in high-purity germanium are reported. The donors observed include phosphorus, arsenic, lithium, a hydrogen-oxygen complex, and three lithium-related complexes. One lithium-related complex designated D(Li,Y) is reported here for the first time. Within experimental accuracy, energies of the excited states with respect to the conduction band are the same for all donors. Fourteen different 1S→excited state transitions (five previously unreported, two others seen for the first time in PTIS from the ground state) have been observed. The Zeeman effect was used to help identify these levels. PTIS lines from the ground state to 2P0 and 3P0 were found to be relatively weak but their intensity was in good agreement with the intensity calculated by means of the Cascade theory. In as-grown samples, linewidth broadening of group V donors was observed that depended on the square root of the dislocation density (etch pit density) and with features expected from deformation potential theory.