Polarization and polarization induced electric field in nitrides - critical evaluation based on DFT studies

TL;DR

This study uses DFT calculations to evaluate the polarity of group III nitrides, comparing different polarization models and their implications for electric fields and surface termination effects.

Contribution

It provides a critical evaluation of polarization calculation methods in nitrides, proposing a physically sound approach that accounts for surface termination and electric field reversal.

Findings

Berry phase polarization solutions vary with volume selection

Surface termination influences polarization and electric field direction

Physically consistent polarization values depend on boundary conditions

Abstract

Density Functional Theory (DFT) calculations were used to evaluate polarity of group III nitrides, such as aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN) providing physically sound quantitative measure of polarity of these materials. Two different approaches to polarization of nitride semiconductors were assessed and the conclusions have been used to develop models. It was shown that Berry phase formulation of the electron related polarization component provides a number of various solutions, different for various selection of the simulated volume. The electronic part gives saw-like pattern for polarization. A total number of these solutions, related to well known scaling of the geometric phase, is equal to the number of valence electrons in the system. Summation with similar pattern for ionic part provides several polarization values. Standard dipole density formulation depends on the selection of the simulation volume in periodic continuous way. Using a condition of continuous embedding into the infinite medium, and simultaneously, the zero surface charge representation at crystal boundary provides to physically sound solution. This solution is corresponding to maximal and minimal polarization values and also corresponds to different physical termination of the crystal surfaces, either bare or covered by complementary atoms. This change leads to polarization and electric field reversal. The polarization and related fields in finite size systems were obtained.