Doping and defect studies of epitaxial gallium nitride

The doping characteristics and defect structure of vapor grown epitaxial GaN were investigated to determine the applicability of thermodynamic models. The doping studies indicated that an equilibrium thermodynamic model successfully describes the experimental behavior of impurity incorporation, solubility limits, compensation, native defect formation, and codoping phenomena in GaN. Hydrogen was found to play a critical role in these processes.; To characterize the doping behavior, epitaxial layers were grown by atmospheric pressure metalorganic vapor phase epitaxy and doped with Mg, Si, and O in a H2 atmosphere. Dopant concentrations were quantified with secondary ion mass spectroscopy (SIMS), and carrier concentrations were measured by Hall effect. Deep level defect concentrations and ionization energies were characterized with steady state photocapacitance and deep level optical spectroscopy.; The incorporation behavior and solubility limits of Mg and Si were analyzed in terms of the thermodynamic model. The linear dependence of the Mg incorporation on the dopant partial pressure was attributed to the formation of Mg-H complexes. Experimental solubility limits of 5 x 1019 cm -3 for Mg, and 3 x 1019 cm-3 for Si are in agreement with first principles thermodynamic calculations in the presence of H2. The compensating defects in p-type GaN:Mg and n-type GaN:Si were attributed to hydrogen and hydrogen-vacancy complexes by comparing the experimental defect formation energies to first principles calculations.; Codoping was investigated to increase p-type GaN conductivity. Analysis with equilibrium solution theory indicated hydrogen, rather than the deliberately added codopant controls acceptor solubility in vapor grown GaN. A nearly constant hole concentration was observed with Mg-Si Codoping. A pairing model, whereby the average acceptor activation energy decreases to as low as 110 meV, was developed to explain the behavior.; The concentrations of compensating deep levels were analyzed in terms of the model. Using photocapacitance, a multiply charged acceptor at E C-3.2 eV in n-type GaN was indicated by the formation energy dependence on the Fermi level. Lowering the Fermi level with Mg doping altered the dominant defects in p-GaN. Levels at 3.1 and 2.7 eV above the valence band are tentatively attributed to the defects involved in the blue and green photoluminescence band in p-GaN, respectively.