General Conditions for Axis Dependent Conduction Polarity

TL;DR

This paper provides a theoretical framework with criteria to identify materials exhibiting axis-dependent conduction polarity, enabling thermoelectric applications without heterojunctions.

Contribution

It derives necessary and sufficient inequalities for ADCP based on thermopower analysis across various materials and verifies them with known ADCP materials.

Findings

Derived transparent inequalities for ADCP emergence.

Verified band-structure characteristics of known ADCP materials.

Provided a set of generic criteria for predicting ADCP in materials.

Abstract

Axis-Dependent Conduction Polarity (ADCP) refers to the phenomenon in which electrical transport within a single material is p-type along one crystallographic direction and n-type along the perpendicular direction. This behavior enables a variety of thermoelectric applications that do not require a heterojunction between two different materials. In this work, we investigate ADCP theoretically and derive a set of generic and quantitative criteria for identifying and predicting materials that exhibit ADCP. Specifically, by analyzing the thermopower for generic metals, semimetals, and semiconductors, we obtain transparent inequalities that are both necessary and sufficient for the emergence of ADCP. Moreover, we review known ADCP materials and verify that their band-structure characteristics and relaxation parameters are consistent with the inequalities derived here.