Phonon spectroscopy measurements at amorphous films

Abstract

Phonon spectroscopy measurements were used to examine the scattering of high frequency phonons (300 GHz-1 THz) in amorphous materials. The experiments were done with the use of time and frequency resolved measurements of the phonon transmission behaviour through amorphous single films of different thicknesses. The typical film thicknesses were of the order of 10 nm. In contrast to the pure amorphous semiconductors Si and Ge our experiments show inelastic phonon scattering processes in the case of SiO 2 and Si:H. This inelastic phonon scattering also occurs when the pure semiconductors Si and Ge are prepared in an O 2 or H 2 atmosphere, but is missing when the preparation process is done in an N 2 atmosphere. In films of the pure semiconductors a-Si and a-Ge we only found evidence to elastic scattering processes. In further experiments at heated a-Si:H samples we could examine the atomical bonded hydrogen to be the center of the inelastic phonon scattering.