PHOTOTHERMAL DEFLECTION SPECTROSCOPY OF HYDROGENATED AMORPHOUS-SILICON AT LOW ENERGIES AND AT LOW-TEMPERATURES

Hydrogenated amorphous silicon (a-Si:H) films are studied by the photothermal deflection spectroscopy (PDS) system, extending the pump beam energy to 0.45 eV and the measurement temperature to 77 K. It is shown that the optical absorption of Coming 7059 glass as substrates are superimposed on the below-gap absorption of a-Si:H films with a low defect density. High-purity quartz with a low impurity and OH radical density is needed for measurements on high-quality a-Si:H. In a-Si:H and a-Si3N4:H the overtone modes of Si-H and N-H stretching vibrations are observed at wavenumbers of 4000-4300 and about 6650 cm(-1) respectively. The extra absorption peaks around 4500 cm(-1) correspond to the optical absorption in the high-pressure gaseous H-2. The techniques for PDS at 77 and about 4.2 K are demonstrated and the sensitivities old at these temperatures are about 5 x 10(-5) and about 10(-3) respectively. The radiative recombination quantum efficiencies of a-Si:H at 300 and 77 K are estimated from PDS using the photoluminescence fatigue effect of a-Si:H with high-power light irradiation. The efficiencies obtained at 300 and 77 K are less than 2 and 12-36% respectively.