High conductivity of Ga-doped rock-salt ZnO under pressure: Hint on deep-ultraviolet-transparent conducting oxides

This letter reports on transport and optical experiments under pressure in thin films of Ga-doped ZnO in both the wurtzite and rock-salt phases. The conductivity of heavily Ga-doped ZnO thin films is shown to decrease by only a factor of 2 in the wurtzite-to-rock-salt phase transition, occurring at about 11.5 GPa, while the optical gap increases from 4 to more than 5 eV. Ga-doped rock-salt ZnO is shown to behave as a deep-ultraviolet-transparent conducting oxide, with resistivity values as low as 10−3Ωcm. The analysis of Burstein–Moss shift and free carrier absorption in rock-salt ZnO yield an estimation of the electron-hole reduced effective mass and electronic dielectric constant. Given the similarity between the electronic structures of rock-salt ZnO under pressure and rock-salt MgxZn1−xO at ambient pressure, this alloy could be a good deep-ultraviolet-transparent conducting oxide.