Nonradiative quenching of EPR signals in germanium-doped AlGaN: evidence for DX-center formation

TL;DR

This study combines experimental photo-EPR measurements and first-principles calculations to demonstrate that germanium acts as a DX-center in AlGaN, affecting its electronic and magnetic properties.

Contribution

It provides the first direct evidence of Ge as a DX-center in AlGaN through combined experimental and theoretical approaches.

Findings

EPR signals appear only after photoexcitation

Thermal annealing reduces the EPR signal

The critical temperature for quenching varies with Al content

Abstract

We present photo-electron paramagnetic resonance (EPR) measurements and first-principles calculations that indicate germanium (Ge) is a DX-center in AlGaN. Our photo-EPR measurements on Ge-doped AlGaN samples show no EPR spectra in the dark, while persistent EPR spectra is observed upon photoexcitation with photon energies greater than ~1.3 eV. Thermally annealing the samples decreased the EPR signal, with the critical temperature to quench the EPR signal being larger in the lower Al-content sample. Using detailed first-principles calculations of Ge in AlGaN, we show all of these observations can be explained by accounting for the DX configuration of Ge in AlGaN.