Gallium concentration dependence of room-temperature near-bandedge luminescence in n-type ZnO:Ga

TL;DR

This study explores how increasing gallium doping in n-type ZnO films affects their optical properties, revealing a systematic blueshift in absorption and enhanced near-bandedge photoluminescence at room temperature, with effects explained by potential fluctuations.

Contribution

It provides new insights into the doping-dependent optical behavior of ZnO:Ga, highlighting the relationship between donor concentration and luminescence characteristics.

Findings

Absorption edge blueshifts with increased Ga doping.

Room-temperature near-bandedge PL intensity generally increases with doping.

Potential fluctuations due to donor distribution cause Stokes shift and PL broadening.

Abstract

We investigated the optical properties of epitaxial \textit{n}-type ZnO films grown on lattice-matched ScAlMgO$_4$ substrates. As the Ga doping concentration increased up to $6 \times 10^{20}$ cm$^{-3}$, the absorption edge showed a systematic blueshift, consistent with the Burstein-Moss effect. A bright near-bandedge photoluminescence (PL) could be observed even at room temperature, the intensity of which increased monotonically as the doping concentration was increased except for the highest doping level. It indicates that nonradiative transitions dominate at a low doping density. Both a Stokes shift and broadening in the PL band are monotonically increasing functions of donor concentration, which was explained in terms of potential fluctuations caused by the random distribution of donor impurities.