Theoretical and experimental investigation of optical absorption anisotropy in $\beta$-Ga2O3

TL;DR

This study combines experimental optical absorption measurements with theoretical analysis to investigate the anisotropy of the optical bandgap in monoclinic $eta$-Ga2O3, revealing polarization-dependent shifts in the bandgap edge.

Contribution

It provides a comprehensive analysis of optical absorption anisotropy in $eta$-Ga2O3$ combining experimental data with advanced theoretical methods, highlighting the polarization-dependent bandgap shifts.

Findings

Bandgap edge varies with light polarization and crystal orientation.

Polarization along the ac plane shows the lowest bandgap onset at 4.5-4.6 eV.

Polarization along b shifts the bandgap onset up by 0.2 eV.

Abstract

The question of optical bandgap anisotropy in the monoclinic semiconductor $\beta$-Ga2O3 was revisited by combining accurate optical absorption measurements with theoretical analysis, performed using different advanced computation methods. As expected, the bandgap edge of bulk $\beta$-Ga2O3 was found to be a function of light polarization and crystal orientation, with the lowest onset occurring at polarization in the ac crystal plane around 4.5-4.6 eV; polarization along b unambiguously shifts the onset up by 0.2 eV. The theoretical analysis clearly indicates that the shift of the b onset is due to a suppression of the transition matrix elements of the three top valence bands at $\Gamma$ point.