Optical properties and structural phase transitions in MgxZn1-xO under hydrostatic pressure

This article reports on the optical properties under pressure of MgxZn1-xO (x < 0.13 +/- 0.2) thin films deposited on mica and fluorite substrates by pulsed-laser deposition. The absorption edge of the semiconductor alloy is measured in both the ambient pressure wurtzite phase and the high-pressure rock-salt phase for several Mg contents. In wurtzite MgxZn1-xO, a larger value of the band-gap is clearly correlated of cation d-levels to the valence band maximum state as the Mg content increases. The wurtzite-to-rock-salt transition pressure is observed to decrease from 9.5 +/- 0.2 (pure ZnO) to 7.0 +/- 0.2 GPa (for x = 0.13), with an almost linear dependence on the Mg content. The same linear dependence on x, with virtually the same slope, is also found for the rock-salt-to-wurtzite reverse transition in the pressure down-stroke. For x . 0.13, the rock-salt phase is observed to be metastable at room pressure, after a pressure cycle up to 15 GPa.