Growth of gallium nitride via iodine vapor phase growth

Thick layers of gallium nitride have been deposited on 1µm thick MOVPE GaN(0001) thin film substrates using a novel vertical iodine vapor phase epitaxy system. The system features three concentric flow zones that separate the reactant gasses until they reached the substrate. Nitrogen flows through the innermost zone and delivers iodine vapor from an external bubbler to the molten Ga maintained at ∼1040 °C and GaI to the substrate; high-purity ammonia flows through the outermost zone; and nitrogen flows through the middle zone to prevent reaction between the growth species at the GaI nozzle. Growth rates greater than 75 µm/hr have been achieved at a V/III ratio of 75. The use of higher V/III ratios resulted in lower growth rates. Optical microscopy of the final growth surfaces revealed spiral hillocks with base diameters as large as 1mm. Increased Ga in the vapor phase resulted in a duplex microstructure containing both hillocks and faceted, oriented crystals overgrowing the hillocks. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)