Plasma-assisted liquid phase epitaxy of gallium nitride using molten gallium.

Pulsed plasma;nitrogen radicals;nitrogen concentration;dissolution;recombination;growth

Daniel Felipe Jaramillo-Cabanzo

University:University of Louisville

Department:Chemical Engineering

关键词: Pulsed plasma;    nitrogen radicals;    nitrogen concentration;    dissolution;    recombination;    growth;   

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=4436&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

Next generation semiconductor materials such as Gallium Nitride (GaN) and Silicon Carbide (SiC) are rapidly replacing Silicon (Si) for high power and high frequency applications due to Si’s inherent limitations. Despite the advantages of GaN over SiC, adoption of GaN has been hindered due to the lack of a cost-effective bulk production technique. Thus, the inability to precure native substrates requires GaN-based architectures to be heteroepitaxially synthesized on non-native substrates, such as sapphire and even SiC. This research seeks to develop a cost effective and scalable method to produce low defect, bulk GaN encouraging the adoption of GaN based devices which ultimately will allow reduction of energy losses in the grid. Specifically, two conceptual methods for the growth of bulk GaN will be explored. The first one is a film-based method, which is based on self-oriented growth of GaN films on a melt gallium layer. In this process, a highly oriented GaN film, made by exposing Ga to plasma-activated nitrogen atoms, is epitaxially thickened into a millimeter-thick GaN film via metalorganic chemical vapor deposition (MOCVD) or halide vapor phase epitaxy (HVPE). The second proposed concept is a crystal-based method. In this process, single crystalline GaN crystals are obtained by nucleation of GaN out of a Ga melt when exposed to nitrogen plasma. Later, those crystals are enlarged via plasma-assisted liquid phase epitaxy. As a first step to develop a plasma-assisted liquid phase epitaxy technique the wetting properties of Ga, as well as the interaction between molten Ga and plasma were studied. It was found that both an increment in temperature and the addition of other elements can improve the wettability of Ga by reducing the surface tension of the molten metal. However, these variables were not as effective as the dissolution of nitrogen radicals into the melt. Absorption/desorption experiments indicated a rapid adsorption/dissolution of the gas into the molten metal when gallium was exposed to plasma. The overall interaction between Ga and plasmas is composed of five processes: (1) surface adsorption, (2) diffusion into the bulk, (3) recombination inside the bulk, (4) surface recombination, and (5) desorption of species from the bulk. The concentration of radicals inside the metal is determined by the rate in which each process is completed. The self-oriented growth of GaN crystals on molten Ga was found to be dependent of the ability of Ga to spread. XRD characterization showed that flat GaN films only presented