The structural,energetic,and electronic properties of lattice highly mismatched ZnY1-x O x(Y = S,Se,Te) ternary alloys with dilute O concentrations are calculated from first principles within the density functional theory.We demonstrate the formation of an isolated intermediate electronic band structure through diluted O-substitute in zinc-blende ZnY(Y = S,Se,Te) at octahedral sites in a semiconductor by the calculations of density of states(DOS),leading to a significant absorption below the band gap of the parent semiconductor and an enhancement of the optical absorption in the whole energy range of the solar spectrum.It is found that the intermediate band states should be described as a result of the coupling between impurity O 2p states with the conduction band states.Moreover,the intermediate bands(IBs) in ZnTeO show high stabilization with the change of O concentration resulting from the largest electronegativity difference between O and Te compared with in the other ZnSO and ZnSeO.
Zinc oxide(ZnO) is a compound semiconductor with a direct band gap and high exciton binding energy.The unique property,i.e.,high efficient light emission at ultraviolet band,makes ZnO potentially applied to the short-wavelength light emitting devices.However,efficient p-type doping is extremely hard for ZnO.Due to the wide band gap and low valence band energy,the self-compensation from donors and high ionization energy of acceptors are the two main problems hindering the enhancement of free hole concentration.Native defects in ZnO can be divided into donor-like and acceptorlike ones.The self-compensation has been found mainly to originate from zinc interstitial and oxygen vacancy related donors.While the acceptor-like defect,zinc vacancy,is thought to be linked to complex shallow acceptors in group-VA doped ZnO.Therefore,the understanding of the behaviors of the native defects is critical to the realization of high-efficient p-type conduction.Meanwhile,some novel ideas have been extensively proposed,like double-acceptor co-doping,acceptor doping in iso-valent element alloyed ZnO,etc.,and have opened new directions for p-type doping.Some of the approaches have been positively judged.In this article,we thus review the recent(2011-now) research progress of the native defects and p-type doping approaches globally.We hope to provide a comprehensive overview and describe a complete picture of the research status of the p-type doping in ZnO for the reference of the researchers in a similar area.
The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding(1) the development of high-quality epitaxy techniques,(2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and(3) the design, realization,and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an isovalent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO.Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk.
