Structural and optical inhomogeneities of Fe doped GaN grown by hydride vapor phase epitaxy

We present the results of cathodoluminescence experiments on a set of Fe doped GaN samples with Fe concentrations of 5x10(17), 1x10(18), 1x10(19), and 2x10(20) cm(-3). These specimens were grown by hydride vapor phase epitaxy with different concentrations of Fe. The introduction of Fe is found to promote the formation of structurally inhomogeneous regions of increased donor concentration. We detect a tendency of these regions to form hexagonal pits at the surface. The locally increased carrier concentration leads to enhanced emission from the band edge and the internal T-4(1)(G)-(6)A(1)(S) transition of Fe3+. In these areas, the luminescence forms a finely structured highly symmetric pattern, which is attributed to defect migration along strain-field lines. Fe doping is found to quench the yellow defect luminescence band and to enhance the blue luminescence band due to the lowering of the Fermi level and the formation of point defects, respectively.