Thermal Conductivity and Specific Heat of Thin-Film Amorphous Silicon

We report the thermal conductivity and specific heat of amorphous silicon thin films measured from 5-300 K using silicon-nitride membrane-based microcalorimeters. Above 50 K the thermal conductivity of thin-film amorphous silicon agrees with values previously reported by other authors. However, our data show no plateau, with a low T suppression of the thermal conductivity that suggests that the scattering of long wavelength, low Q vibrations goes as Q2. The specific heat shows Debye-like behavior below 15 K, with theta(D) = 487 +/- 5 K, and is consistent with a very small contribution of tunneling states in amorphous silicon. Above 15 K, the specific heat deviates less from Debye behavior than does its crystalline allotrope, indicating no significant excess modes (boson peak) in amorphous silicon.