S. Nonomura et al., PHOTOTHERMAL DEFLECTION SPECTROSCOPY OF HYDROGENATED AMORPHOUS-SILICON AT LOW ENERGIES AND AT LOW-TEMPERATURES, Philosophical magazine. B. Physics of condensed matter. Structural, electronic, optical and magnetic properties, 69(2), 1994, pp. 335-348
Hydrogenated amorphous silicon (a-Si:H) films are studied by the photo
thermal 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 su
perimposed on the below-gap absorption of a-Si:H films with a low defe
ct density. High-purity quartz with a low impurity and OH radical dens
ity 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) respectivel
y. The extra absorption peaks around 4500 cm(-1) correspond to the opt
ical absorption in the high-pressure gaseous H-2. The techniques for P
DS 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 an
d 77 K are estimated from PDS using the photoluminescence fatigue effe
ct of a-Si:H with high-power light irradiation. The efficiencies obtai
ned at 300 and 77 K are less than 2 and 12-36% respectively.