Equations of state for ZnO and MgZnO by high pressure x-ray diffraction

Abstract

MgZnO alloys are potentially important semiconductors for UV optoelectronics and other applications. Since device heterostructures are under significant strain, it is important to determine the elastic properties of these materials, in the bulk and nanoscale. In this work, the equations of state were obtained for ZnO and MgxZn1-xO alloys under hydrostatic pressure, using x-ray diffraction. The equations of state were found to be insensitive to Mg content up to x = 0.2. The pressure dependence of the c/a ratio also did not depend on Mg content, within experimental uncertainty. Combining these results with previous ultrasonic measurements, the following elastic constants were determined to be valid for wurtzite MgxZn1-xO (x≤ 0.2): C11 = 207 GPa, C12 = 118 GPa, C33 = 210 GPa, and C13 = 106 GPa. These elastic constants yield a bulk modulus of 143 GPa and c/a slope of -3×10-4GPa-1. Nanocrystals showed the same bulk moduli as their bulk counterparts. However, nanocrystals showed consistently steeper c/a slopes, suggesting subtle differences in their elastic constants.