Preparation and characterization of thin, atomically clean gallium nitride(0001) and aluminum nitride(0001) films and the deposition of thick gallium nitride films via iodine vapor phase growth

The research conducted for this dissertation involved two tasks important to the achievement of (1) improved interfaces in future III-nitride devices and (2) GaN substrates for homoepitaxial growth of III-nitride films and material device structures. The initial phase of this work determined an effective technique for the removal of oxygen and hydrocarbon contamination from GaN(0001) and AlN(0001) surfaces. Through the combined use of several surface evaluation techniques, a chemical vapor treatment with ammonia in a UHV environment was developed. The optimal conditions for GaN were 860°C for 15 minutes at 10-4 Torr, and for AlN were 1120°C for 30 minutes at 10-4 Torr. The surface microstructures of each material were undamaged, and important electrical and optical properties of the treated surfaces were determined. The technique was adapted to clean the surface of a GaN thin film substrate prior to homoepitaxial growth via metal-organic vapor phase epitaxy (MOVPE). Introducing ammonia into the gas mixture during heating resulted in reduction of the contamination at the interface between the substrate and a subsequently grown GaN film.; Rapid growth of thick GaN films was achieved via the reaction between gallium iodide species and ammonia on various substrates. The iodine and gallium transport rates in the custom reactor were lower than expected from thermodynamic equilibrium calculations due to high gas flow rate relative to the volume of the iodine and gallium sources. The gallium transport remained a function of the iodine flow rate, and the growth rate was a function of the amount of gallium delivered to the seed. The maximum growth rate achieved was 155 mum/hr for 1 hour. Cracking was observed in all films grown via IVPG, even when the substrate was changed from sapphire to SIC. Use of a gold layer as an in-situ mask did not reduce the cracking when the GaN was deposited over the gold layer.