Invited talk abstract

Growth of GaN under high pressure-high temperature conditions allows to obtain large size high quality GaN single crystals. These crystals have high concentration of free electrons, most likely due to high concentration of O impurity replacing nitrogen in N sublattice. Incorporation of oxygen impurity during high pressure growth of GaN single crystals will be investigated. It will be shown that the dissolution of oxygen in liquid gallium leads to dissociation of O2 molecule. The dissociation process proceeds without energy barrier. Doping of Mg during growth leads to change of electric properties of GaN crystals - they become highly resistive. Mg-doping changes morphology of GaN plate-like crystals. The physical properties of GaN:Mg crystals will be reviewed and compared with undoped GaN crystals. Beryllium doping is considered as an alternative route to p-type of GaN. The doping with Be during growth increases resistivity of Be doped GaN. However optical properties of Be doped GaN crystals are different. These properties will be compared with Ng-doped and undoped GaN crystals.