Thickness dependence of the strain, band gap and transport properties of epitaxialIn2O3 thin films grownon Y-stabilised ZrO2(111)

Abstract

Epitaxial films of In2O3 havebeen grown on Y-stabilised ZrO2(111) substrates by molecular beam epitaxy over a range of thicknesses between 35 and420 nm. The thinnest films are strained, but display a ‘cross-hatch’ morphologyassociated with a network of misfit dislocations which allow partial accommodationof the lattice mismatch. With increasing thickness a ‘dewetting’ process occursand the films break up into micron sized mesas, which coalesce into continuousfilms at the highest coverages. The changes in morphology are accompanied by aprogressive release of strain and an increase in carrier mobility to a maximum value of73 cm2 V − 1 s − 1. The optical band gap in strained ultrathin films is found to be smaller than for thickerfilms. Modelling of the system, using a combination of classical pair-wise potentials and abinitio density functional theory, provides a microscopic description of the elasticcontributions to the strained epitaxial growth, as well as the electronic effects that give riseto the observed band gap changes. The band gap increase induced by the uniaxialcompression is offset by the band gap reduction associated with the epitaxial tensile strain.