Accurate experimental determination of the Poisson’s ratio of GaN using high-resolution x-ray diffraction

Moram, M A and Barber, Z H and Humphreys, C J

Abstract.

An accurate Poisson’s ratio value of 0.183±0.003 for a typical c-axis-oriented GaNfilmgrown by metal-organic vapor-phase epitaxy deposition has been determined using a wafer bending apparatus combined with high-resolution x-ray diffractionlattice parametermeasurements. The precision of this method has improved ten fold over typical methods used for thin film samples, enabling future study of the effects of doping, compositional changes, or structural defects on the Poisson’s ratio of GaN. The obtained Poisson’s ratio value is lower than most calculated values, which is attributed to the presence of strain-relieving edge dislocations in the GaN sample. Unstrained filmlattice parameters can also be found using this method, and are shown to be a=3.1884±0.0002Å and c=5.1850±0.0002Å (assuming an unstrained c/a ratio of 1.6262). A brief review of Poisson’s ratio and unstrained lattice parameter values for GaN in the literature is also given.

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Department of Materials
Imperial College London
Royal School of Mines
Exhibition Road
London, SW7 2AZ - UK