EVIDENCE OF WEAK PHONON COUPLING TO THE SI-H STRETCHING MODES IN A-SIH

We have observed that the infrared-active stretching modes of hydrogen in device-quality a-Si:H films are redshifted as the temperature incr eases. Over the range of temperatures studied, 100-600 K, the shift is approximately linear with temperature, 0.035 cm-1 K-1, and shows a to tally reversible behavior. We have established that changes in the pol arization of the material, via changes of the dielectric constant with temperature, can lead to small shifts, but cannot explain the magnitu de of the experimentally observed effect. We compare our results with a similar observation made on well defined hydrogen-terminated Si surf aces. In that case, the shift was attributed to the coupling of the hy drogen stretching motion with lower-frequency phonons. We propose that an analogous coupling mechanism is present in the a-Si:H structure.