Polaron transport of amorphous semiconductors with embedded crystallites

TL;DR

This paper models the electronic transport in amorphous semiconductors with embedded crystallites, revealing how crystallite size and carrier concentration influence conductivity and thermoelectric properties near room temperature.

Contribution

It introduces an effective-medium approach to analyze how embedded crystallites affect transport properties in amorphous semiconductors, highlighting the role of trapping and mobility.

Findings

Crystallites can trap carriers when their energy is lower than the amorphous phase.

Electrical conductivity can be suppressed or enhanced depending on carrier concentration.

Seebeck coefficient remains unaffected by crystallite growth.

Abstract

Near-room-temperature electronic transport of annealing induced semiconducting crystallites embedded within its amorphous counterpart is treated within the effective-medium approach. As such, the mixtures transport coefficients become smooth functions of those of its two components. Carrier mobilities in the crystallites are assumed much larger than those of the amorphous phase. Nonetheless, crystallites act as macroscopic traps when their carriers energies lie below those in the amorphous phase. Then the mixtures dc conductivity falls below that of the amorphous phase at low enough carrier concentrations. However, with increasing carrier concentration the shifting chemical potential diminishes this trapping effect enabling crystallites larger mobilities to drive the mixtures electrical conductivity above that of the amorphous phase. Meanwhile the Seebeck coefficient remains insensitive to the annealing-induced introduction and growth of embedded crystallites. These features are qualitatively similar to those reported for an amorphous organic polymer with annealing-induced embedded crystallites.