Growth and characterization of freestanding gallium nitride substrates by the hydride-metalorganic vapor phase epitaxy technique

A novel chemistry was investigated and characterized for the atmospheric-pressure deposition of gallium nitride films that combined the advantages of the high crystal quality of metalorganic vapor-phase epitaxy (MOVPE) with the high growth rate of hydride vapor phase epitaxy (HYPE). The limits of the hydride-metalorganic vapor phase epitaxy (H-MOVPE) growth envelope between 500°C and the furnace-limited 950°C were investigated and compared to literature results. Variation of process parameters such as V/III ratio and HCl/Ga ratio was also researched, and the effects upon film quality were tabulated. Films were characterized by growth rate measurement, X-ray diffraction (XRD), atomic force microscopy (AFM), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and photoluminescence (PL). The best results for single-crystalline GaN film growth on sapphire were obtained at 950°C, an ammonia flow rate of 500 sccm, and an HCl/Ga ratio of 2:1.; Thick gallium nitride films were grown upon lithium gallium oxide (LGO) and lithium aluminum oxide (LAO) substrates, which were nearly lattice-matched to gallium nitride. While the films grown upon LGO possessed superior crystal quality and surface morphology, the films grown upon LAO possessed greater mechanical stability and much lower impurity concentrations. Oxygen incorporation, in particular, was very high for films grown upon LGO. Investigation by SIMS revealed evidence of decomposition of the LGO substrate during hydride growth, but no decomposition of the LAO.; Finally, the thermodynamics of both the growth chemistry and nitride solid solutions were investigated. Theoretical variations of growth rate with process parameters were predicted and compared with experiment. While general trends between theoretical and experimental growth rates were similar, the theoretical results were not descriptive of the experimental without arbitrarily increasing the stability of the gallium nitride solid phase. The solid solution behavior of the nitrides was modeled by regular solution theory, using several models for interaction parameters. An empirical model was developed for sole use with nitrides and compared with literature models. Experimental results for the InGaN system proved the model statistically indistinguishable from other published numerical and theoretical models.