Photoluminescence and photoconductivity of Si- and Ge-rich SiGe bulk crystals

We have investigated Si- (0 less than or equal to x less than or equal to 0.13) and Ge-rich (0.90 less than or equal to x less than or equal to 1) Si1-xGex bulk crystals by photoluminescence and photoconductivity measurements. The small linewidths of the near band edge luminescence of less than 4 meV demonstrate the high quality of the crystals. Luminescence linewidth, line shape, and intensity ratios of transitions with and without phonon participation reveal a stronger influence of alloy effects on excitons on the Ge-rich side compared with the Si-rich side. Photoconductivity spectra of boron doped Si-rich and phosphorus doped Ge-rich Si1-xGex crystals show the influence of alloy composition and alloy fluctuations on the impurity levels. The shift of the photoconductivity spectra with increasing Si or Ge concentration indicates the change of the ground state energy of the impurity with changing alloy composition. (C) 1998 American Vacuum Society.