Preparation and Characterization of Thin, Atomically Clean GaN(0001) and AlN(0001) Films and the Deposition of Thick GaN Films via Iodine Vapor Phase Growth

IVPG;HVPE;bulk growth;Surface science

Mecouch, William John ; Dr. Robert F. Davis, Committee Co-Chair,Dr. Robert J. Nemanich, Committee Co-Chair,Dr. Zlatko Sitar, Committee Co-Chair,Dr. George Rozgonyi, Committee Member,Mecouch, William John ; Dr. Robert F. Davis ; Committee Co-Chair ; Dr. Robert J. Nemanich ; Committee Co-Chair ; Dr. Zlatko Sitar ; Committee Co-Chair ; Dr. George Rozgonyi ; Committee Member

University:North Carolina State University

关键词: IVPG;    HVPE;    bulk growth;    Surface science;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/4793/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

The research conducted for this dissertation involved two tasks important to the achievement of (1) increased breakdown fields and improved ohmic and rectifying contacts in future III-nitride devices and (2) GaN substrates for homoepitaxial growth of III-nitride films and material device structures with low densities of defects.The initial phase of this work involved the determination of an effective technique for the removal of oxygen and hydrocarbon contamination from GaN(0001) and AlN(0001) surfaces without damage to the as-received microstructure.It was determined via the combined use of x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, low energy electron diffraction, and atomic force microscopy (AFM) that a chemical vapor treatment with ammonia in an ultrahigh vacuum environment removed this contamination from these surfaces.The optimal conditions for both n- and p-type GaN were 860°C for 15 minutes at 10⁻⁴ Torr.Complete removal of the contaminants from the AlN surface required 1120°C for 30 minutes at 10⁻⁴ Torr .The microstructures of the surfaces of each material were undamaged.Important electrical and optical properties of the treated surfaces were determined, including the band bending, the electron affinity, and the elemental core level positions.The technique was subsequently employed to clean the surface of a GaN thin film substrate previously deposited and contained within a metal-organic vapor phase epitaxy (MOVPE) reactor.The introduction of ammonia into the gas mixture during heating resulted in substantial reduction in the contamination on this substrate, as determined via depth profile secondary ion mass spectroscopy at the heteroepitaxial interface between the substrate and a subsequently grown GaN film.This cleaning procedure also improved the microstructure of the homoepitaxial layer.The rapid growth of thick GaN films was achieved via the reaction between I-containing species and ammonia on various substrates.The concentrations of iodine and gallium transported in the iodine vapor phase growth (IVPG) reactor developed in this program were lower than expected from thermodynamic equilibrium calculations due to a high carrier gas flow rate relative to the volume of the iodine source bubbler and the gallium source.However the gallium transport remained a function of the iodine flow rate, and the growth rate wasa function of the amount of gallium being delivered to the seed.Increasing the growth timedecreased the growth rate within the first hour of growth, indicating that growth transients were present at the initial stages of growth and related to either the instantaneous concentration of iodine in the carrier gas or the temperature of the seed holder.The maximum growth rate achieved was 155 μm/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.