First-principles Studies Of N-In And N-Mg Codoping ZnO Under High Pressure

Defects and impurities will have impact on the physical properties amongsemi-conduct materials, and they play a decisive role about semi-conduct application.ZnO in the range of10GPa is a direct band gap semi-conduct and the width of bandgap is3.37eV, which in principle allow ZnO to have important impacts in the blueand UV regions. Therefore, researchers pay more attention to ZnO. However, there isserious doping asymmetry problems in ZnO system, that is, ZnO system can be dopedeasily p-type and not n-type. It is impossible to achieve relative application in the blueand UV regions. Thus, achieving better p-type ZnO becomes the focus of researchinterest.We use codoping method to design p-type ZnO (N-In and N-Mg codope ZnO).The electronic properties and the formation enthalpy, blind energy and ionizationlevels of ZnO codoped with indium and nitrogen are calculated by first principlesdensity-functional theory (DFT) at0and10GPa. The (In-N) complex at10GPaproduces fully occupying dopant band on the valence band maximum (VBM) ofwurtzite ZnO. Under the pressure of10GPa, more nitrogen atoms tending to blind the(In-N) system lead to the (In-xN)(x=2-4) with more acceptors and slightly largertransition levels than the same complexes at0GPa, indicating that the pressure canimprove the concentration of acceptors in defect state. The formation enthalpy iscalculated by using N2O and the formation enthalpy of In-xN decreased with theincrease of N, and the formation enthalpy of In-4N is lowest. At the10GPa， theformation enthalpy of complexes In-3N and In-4N is lower than that of0GPa, indicating that the solubility of the two complexes increase. But the formationenthalpies of In-2N and In-N increase, and the pressure decrease the solubility of thetwo complexes. At0GPA, the ionization energies of In-xN are lower than the singledopant, and these values slightly increase with pressure. Under the high pressure, thecomplexes In-xN except (In-4N)3-convert from repulsive interactions to attraction.Among the (In-xN) complexes at0and10GPa, the cluster (In-4N) at10GPa has alowest formation enthalpy for N2O source of nitrogen.The (In-2N) complex of highpressure prefers to bind other N atoms on the nearest O location at different chargestates, indicating that the defect pairs can be stable under high pressure. At10GPa,the (In-4N) complex has the lower formation enthalpy, slightly larger ionization levelsand better binding energy, which can produce more stable p-type conductivity thanthe complexes under zero pressure.The formation enthalpy of MgZnat10GPa is higher than that at0GPa, whichindicates high pressure can reduce the solubility in the range of10GPa. The MgZnreduces the coupling interaction between p and d orbits, because it introduces Mgatoms with no d orbits to occupy Zn atoms in ZnO system. By the analysis of DOSabout complex (N-4Mg), its valence band maximum is decided by the energy of porbit in the system. Although the concentration of N element is less than O element inthe complexes, it has more contributions than O element by analyzing the contributionof different elements’ p orbit, and these will contribute to forming p-type conductivity.Comparing with the condition of0GPa, the complex (N-4Mg) at10GPa has thestability of defect pairs. The complex (N-4Mg) under the high pressure has lowerionization levels and the bond ability of N atoms is stronger than the bond ability of Oatoms. By calculating the formation enthaplies of complex (N-4Mg) at differentpressure, we found that the pressure can reduce the solubility of defect pairs.