Poster abstract

P-type conduction of GaN is typically obtained by Mg doping which acts as an acceptor. High acceptor concentrations are necessary for many applications but compensation effects limit the achievable free hole concentrations, especially in the samples grown by metal organic vapour phase epitaxy (MOVPE). We studied several series of GaN samples grown by MOVPE and Molecular beam epitaxy (MBE) doped with different Mg concentrations by photoluminescence (PL), Hall and SIMS measurements. For the MOVPE samples a saturation of the hole density vs Mg concentration was observed. The PL was strongly dependent on the Mg concentration. For low doped samples the donor acceptor pair recombination at 3.26 eV was observed, while in the medium/highly doped samples a band at 2.9/2.7 eV dominated. In the MBE samples, independent of the Mg concentration, both bands were seen with rather constant intensity ratios. Also no saturation of the free hole concentration was observed. A first model to gain understanding on the compensation behaviour in MOVPE GaN:Mg was developed by Kaufmann et al [1]. We extended these calculations by considering the formation energies of defects such as VN, VNH and H [2] and also by taking into account the differences between these two growth processes (like temperature and hydrogen presence). The good agreement, between these calculations and our experimental results, allows us to formulate a model explaining the compensation mechanism in MOVPE and also in MBE GaN:Mg.

[1] U. Kaufmann, P. Scholtter, H. Obloh, K. Kohler, Phys. Rev. B 62, 10867 (2000) [2] Chris G. Van de Walle, Phys. Rev. B 56, 10020 (1997)