OMVPE of GaN and AIN films by metal alkyls and hydrazine

Thin films of GaN have been grown on A1₂O₃, Si and GaAs using trimethylgallium and hydrazine (N₂H₄) in N₂ at atmospheric pressure. Growth proceeded by the formation of a room temperature adduct which decomposed to form GaN in the temperature range 425-960°C. Growth coefficients were about 3 μm/mmol (of TMG) for growth temperatures above 650°C. The films grown below 600°C were yellow and polycrystalline on all substrates. Hall mobilities as large as 50 cm²/V·s (n = 1×10²⁰ cm^-3) were obtained for films grown at 900°C with V III = 20. The mobilities were about 1 cm²/V·s (n = 6×10¹⁹ cm^-3) below 650°C. The impurities in the films were O (≈ 2%) and C (<1%) for all growth temperatures. Estimates were made for the room temperature LO and TO phonons of 92 and 67 meV respectively. UV transmission data and the photoresponse of the films show an impurity band about 2.5 ev below the conduction band, probably due to O related defects. A1N was also deposited via the decomposition of an adduct formed by the room temperature reaction between trimethylaluminium and N²H⁴. Films deposited at 575 and 785°C had a rough surface morphology.