# Band-to-band transitions, selection rules, effective mass and exciton binding energy parameters in monoclinic \beta-Ga2O3

## TL;DR

This study combines experimental ellipsometry and advanced density functional theory to analyze the anisotropic optical and electronic properties, including excitonic effects and effective masses, of monoclinic 2O3, providing detailed insights into its band-to-band transitions.

## Contribution

It introduces a comprehensive eigen polarization model for dielectric response analysis and compares experimental results with state-of-the-art DFT calculations for 2O3.

## Key findings

- Identification of polarization-dependent critical point structures.
- Determination of anisotropic effective mass parameters for electrons and holes.
- Quantification of exciton binding energies consistent with experimental data.

## Abstract

We employ an eigen polarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic \beta-Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75 eV--9 eV. The eigen polarization model permits complete description of the dielectric response, and we obtain single-electron and excitonic band-to-band transition anisotropic critical point structure model parameters including their polarization eigenvectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using a recently proposed Gaussian-attenuation-Perdue-Burke-Ernzerhof hybrid density functional, and we present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their exciton binding energy parameters, in excellent agreement with our experimental results. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions, where the observed transitions are polarized closely in the direction of the lowest hole effective mass for the valence band participating in the transition.