# Thermal conductivity for III-V and II-VI semiconductor wurtzite and zinc-blende polytypes: the role of anharmonicity and phase space

## TL;DR

This study uses ab initio calculations to analyze and predict the thermal conductivity differences between cubic and hexagonal phases of semiconductors, considering anharmonicity and phase space effects, and explores tuning these properties in nanowires.

## Contribution

It introduces a predictive method for determining the more conductive phase in semiconductors based on anharmonicity and phase space, advancing understanding of thermal transport in different crystal structures.

## Key findings

- Cubic phase exhibits higher anharmonicity than hexagonal.
- Accessible phase space favors hexagonal phase conductivity.
- Nanowire diameter can tune the ratio of thermal conductivities.

## Abstract

We calculate the lattice thermal conductivity ($\kappa$) for cubic (zinc-blende) and hexagonal (wurtzite) phases for 8 semiconductors using $\textit{ab initio}$ calculations and solving the Phonon Boltzmann Transport Equation, explaining the different behavior of the ratio $\kappa_{\rm hex}/\kappa_{\rm cub}$ between the two phases. We show that this behavior depends on the relative importance of two antagonistic factors: anharmonicity, which we find to be always higher in the cubic phase; and the accessible phase space, which is higher for the less symmetric hexagonal phase. Based on that, we develop a method that predicts the most conducting phase---cubic or hexagonal---where other more heuristic approaches fail. We also present results for nanowires made of the same materials, showing the possibility to tune $\kappa_{\rm hex}/\kappa_{\rm cub}$ over a wide range by modifying their diameter, thus making them attractive materials for complex phononic and thermoelectric applications/systems.