Direct experimental determination of the spontaneous polarization of GaN

TL;DR

This paper introduces a universal optical method to directly measure the spontaneous polarization in GaN crystals using emission energies from stacking faults, validated by theoretical calculations, providing a precise value for Psp.

Contribution

The study presents a novel experimental approach combining spectroscopy and electrostatic modeling to accurately determine GaN's spontaneous polarization without assumptions.

Findings

Measured Psp of GaN as -0.022±0.007 C/m².

Validated experimental results with density-functional theory calculations.

Provided a universal method applicable to other wurtzite semiconductors.

Abstract

We present a universal approach for determining the spontaneous polarization Psp of a wurtzite semiconductor from the emission energies of excitons bound to the different types of stacking faults in these crystals. Employing micro-photoluminescence and cathodoluminescence spectroscopy, we observe emission lines from the intrinsic and extrinsic stacking faults in strain-free GaN micro-crystals. By treating the polarization sheet charges associated with these stacking faults as a plate capacitor, Psp can be obtained from the observed transition energies with no additional assumptions. Self-consistent Poisson-Schroedinger calculations, aided by the microscopic electrostatic potential computed using density-functional theory, lead to nearly identical values for Psp. Our recommended value for Psp of GaN is -0.022+/-0.007 C/m^{2}.