Thermal Expansion and Gruneisen Parameters of Amorphous Silicon: A Realistic Model Calculation

TL;DR

This paper models the thermal expansion and Gruneisen parameters of amorphous silicon, revealing suppressed diversity in parameters, large negative values in certain modes, and lower, sample-dependent thermal expansivity compared to crystalline silicon.

Contribution

It provides a realistic model calculation of thermal properties in amorphous silicon, highlighting differences from crystalline silicon and the impact of localized modes.

Findings

Gruneisen parameters are less diverse in amorphous silicon.

High-frequency localized and low-frequency resonance modes have large negative Gruneisen parameters.

Thermal expansivity in amorphous silicon is lower and sample dependent.

Abstract

Using a realistic model, the mode Gruneisen parameters and the temperature dependent coefficient of linear thermal expansion are calculated for amorphous silicon. The resulting values of the Gruneisen parameters differ from the crystalline case in having all diversity suppressed, except for a minority of high-frequency localized and low-frequency resonance modes. The latter have very large, mostly negative Gruneisen parameters (up to -31), caused by volume driven internal strain. As a result, the values for thermal expansivity are lower than those of crystalline silicon and are sample dependent.