Computer Simulation On Structural, Electronic And Optical Properties Of ZnO And Its Alloys

ZnO and ZnO-based alloys have gained increasing interests in the semiconductor research community because of their large direct band-gap and large exciton binding energy which account for their potential applications in optoelectronic devices. There have been large quantities of researches on the optoelectronic properties of the stable wurtzite phase and its high-pressure phase transitions. Recently, the successful reservation of the high-pressure cubic phase to ambient condition as a metastable phase has provided a wonderful advantage for extending the optoelectronic properties. We thus focus on the physical properties of the metastable phase in this work. And as a result, some important references to the technologic applications of this important material are provided.In this work, the theoretical calculations are performed using the first-principles pseudopotential method, in which we employ the PW-91 function of the generalized gradient approximation available in the CASTEP code together with plane wave basis sets for expanding the periodic electron density.The structural, electronic and the optical properties for wurtzite, zinc-blende and metastable rock-salt ZnO are comparatively investigated in detail. A negative differential conduction effect is predicted for the metastable rock-salt ZnO. The stronger electron-photon coupling and the wider optical response region in the metastable rock-salt ZnO make it more suitable for optical applications especially in the extremely short-wave region (25³5 nm). The optical mechanism of the metastable cubic phase of the orderedMg_xZn_1-xO alloy (x<33%) at ambient condition is investigated and compared to those of the wurtzite phase. The cubic alloy is determined to have a stronger electron-photon coupling, an optically more sensitive Mg 2p state, a larger static dielectric constant, and two metallic response regions, which also suggests more promising applications in optoelectronic devices. The existence of Mg provides a wonderful advantage for the optional modulation of the high energy response region.