Far infrared spectroscopy of semiconductors at large hydrostatic pressures

The combination of high resolution far infrared spectroscopy and large hydrostatic pressures produced by diamond anvil cells (DAC) offers a unique approach to the study of dopants, defects, and bandstructure related properties of semiconductors. The problem of small optical throughputs typical of DACs has been solved. Using this unique tool, we have obtained several new results, including the discovery of a local vibrational mode of the DX center in GaAs:Si and the demonstration that the DX center is a negative-U defect. We have also discovered the first evidence of DX centers in InP and studied the ground to bound excited state transitions of shallow impurities in GaAs at pressures at which GaAs is an indirect bandgap semiconductor with its conduction band minimum near the X symmetry point.