In-situ and post-growth investigation of low temperature Group III-nitride thin films deposited via MOCVD

Group III-nitride semiconductors are a special class of materials with unique properties. They are direct bandgap materials, which range from 1.9 eV for InN and 3.4 eV for GaN to 6.2 eV for AlN, making them excellent candidates for optoelectronic devices. The best quality material is grown using Metalorganic Chemical Vapor Deposition (MOCVD) where most processing is developed with a trial and error approach. There is wide agreement that monitoring techniques for process parameters could vastly improve reproducibility and wafer throughput.; The first part of this research focused on the real-time, in-situ monitoring and control of multicomponent gas phase concentrations for the growth of GaN. An optical monitoring technique was developed based upon Ultraviolet Absorption Spectroscopy (UVAS) coupled with Principal Component Regression (PCR). This technique was shown to accurately monitor the pure component partial pressures of two reactant species in a multicomponent gas stream. This monitoring technique was then used in a multivariable feedback control strategy to simultaneously control the gas phase concentrations of Triethylgallium and ammonia diluted in H₂.; This project also focused on several important growth parameters and their effect on the solid phase properties of low temperature buffer layers of GaN and AIN. Growth temperature, V/III molar ratio, and total reactor pressure were investigated to determine effects on stoichiometry, growth rate, microstructure, and morphology. Post-growth analysis was performed using Auger Electron Spectroscopy depth profiling, X-Ray Diffraction, and Scanning Electron Microscopy. Results show that gas phase reactions and adduct formation play a major role in the deposition process at low temperatures. Parasitic gas phase reactions hinder the incorporation of gallium when using Triethylgallium (TEG) as the gallium source. It was found that the gas phase reaction between TEG and ammonia form low vapor pressure polymeric chains which condense out of the vapor phase eliminating most of the reactant species. Excellent, well-characterized AlN buffer layers were deposited using Trimethylaluminum (TMA) and ammonia and were also shown to experience gas phase adduct formation. These intermediate adducts are a necessary step for depositing AlN thin films using TMA and NH ₃ where it was shown to be detrimental for TEG and NH₃ mixtures.