The Hybrid Density Functional Theory Study Of Wurtzite Semiconductors Under High Pressure

Structural phase transition, band structure and elastic properties of wurtzitesemiconductors under hydrostatic pressure are systematically studied via firstprinciples calculations. Compared with Generalized Gradient Approximation (GGA)and Local Density Approximation (LDA), we use the HSE06range-separated hybridfunctional and have a result that it is better to calculate the energy gap by usingHSE06rather than Density Functional Theory (DFT). The energy gap calculated withHSE06is close to experimental value. Several results reveal that if we take no accountof the specific values, they have same tendency and properties. Meanwhile we draw aconclusion that:(1) The wurtzite semiconductors have a structural phase transition under hydrostaticpressure. The results exhibit behavior that wurtzite phase which is stable state changesto graphite-like phase which is non-stationary and can be called h-MgO phase. Thisphase transition is similar with the large uniaxial compressive strains and the largebiaxial tensile strains.(2) At the process of structural phase transition of wurtzite semiconductors, bandstructures are also changed from direct band gap to in-direct band gap. For instance,before the phase transition ZnO have a direct band gap which CBM and VBM areboth at, and after the phase transition Eg have a suddenly increasing at H point invalence band. Here P=58GPa and ZnO changed from direct band gap to in-directband gap.(3) With the increasing of hydrostatic pressure, calculated results review that theenergy gap increase along with the pressure. This is different with the uniaxial andbiaxial strains. At these two conditions Eg decreases when strains increase, especiallythe Eg of GaN in the large biaxial compressive strains decrease to zero so as to muchstrong electrical conductivity.(4) The super-cell materials have wide spread applies in the fields of photoelectricitydevices. We calculated the properties of AlGaN which has a structure of1×1×2. Andits results show that it has a similar properties with wurtzite semiconductors. Thetheoretical calculated function of energy gap: Eg(x)=6.2x+3.4(1-x)-x(1-x). Whenx=0.5, then Eg=4.55eV, and our experimental result is3.90eV.