Determination of Mg composition in MgxZn1−xO alloy: Validity of Vegard’s law

Abstract

Vegard’s law and inductively coupled plasma atomic emission spectrometry were employed to determine the Mg composition in MgxZn1−xO layers deposited on 6H–SiC substrates. With the increase of Mg composition in MgxZn1−xO layers, the c-axis length decreased by 5.2048−0.072x, while the a-axis length increased to 3.2491+0.047x. The lattice constants estimated by Vegard’s law and a theoretical model exhibited an uncertainty of ∼3% that has been attributed to the ∼2% lattice misfit in the MgO∕ZnO materials system. Localized exciton peaks of MgxZn1−xO alloy in photoluminescence (PL) measurements disappeared completely, while the neutral donor-acceptor pair and 1-longitudinal optical-phonon energies decreased rapidly with the increase of Mg composition. These PL data do not comply with Vegard’s law. The asymmetric behavior in the MgxZn1−xO alloy is the subject of locally disordered Mg potential fluctuations and an artifact of the cMgO and aMgO lengths calculated theoretically.