Observation of additional excited-state lines of indium in silicon

Absorption spectra in the region 1100 to 1300 ${\mathrm{cm}}^{-1\mathrm{}}$ for silicon which has an indium concentration of approximately 4.2 × ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are presented. The spectra were obtained with both grating and Fourier-transform spectrophotometers. Previously unreported indium excited-state lines are observed, and the existence of a line previously reported as weak or doubtful is confirmed. The energy-level spacings for the additional indium lines are shown to be in good agreement with the energy-level spacings for the corresponding boron, aluminum, and gallium lines.