Influence of crystallization front direction on the Mg-related impurity centers incorporation in bulk GaN:Mg grown by HNPS method

We studied the incorporation of Mg-related impurity centers in GaN crystals depending on the direction of the crystallization front. Two series of GaN crystals - (i) undoped and (ii) Mg-doped - were grown by High Nitrogen Pressure Solution (HNPS) method under otherwise identical conditions. Each series contained four samples with (101¯0), (112¯0), (202¯1¯) and (202¯1) orientations. The low-temperature photoluminescence (PL) spectroscopy was used for characterization of the obtained crystals. The observed differences in the PL spectra of GaN:Mg crystals suggested that Mg incorporation in GaN grown by HNPS method depends considerably on the orientation of crystallization front. The concentration of Mg impurity incorporated into the GaN crystals subsequently increases for the following sequence of planes: (101¯0), (112¯0), (202¯1¯) and (202¯1). For (101¯0), (112¯0) and (202¯1¯) planes the blue band is related only to ON - MgGa donor-acceptor pair (DAP) transitions, while for (202¯1) plane the incorporation of Mg-H complexes occurs additionally to the formation ON - MgGa DAP.