MOCVD growth of GaN-based high electron mobility transistor structures

University dissertation from Linköping : Linköping University Electronic Press

Abstract: The present work was to improve the overall quality of GaN-based high electron mobility transistor (HEMT) epitaxial structures grown on semi-insulating (SI) SiC and native GaN substrates, using an approach called bottom-to-top optimization. The bottom-to-top optimization means an entire growth process optimization, from in-situ substrate pretreatment to the epitaxial growth and then the cooling process. Great effort was put to gain the understanding of the influence of growth parameters on material properties and consequently to establish an advanced and reproducible growth process. Many state-of-the-art material properties of GaN-based HEMT structures were achieved in this work, including superior structural integrity of AlN nucleation layers for ultra-low thermal boundary resistance, excellent control of residual impurities, outstanding and nearly-perfect crystalline quality of GaN epilayers grown on SiC and native GaN substrates, respectively, and record-high room temperature 2DEG mobility obtained in simple AlGaN/GaN heterostructures.The epitaxial growth of the wide bandgap III-nitride epilayers like GaN, AlN,  AlGaN, and InAlN, as well as various GaN-based HEMT structures was all carried out in a hot-wall metalorganic chemical vapor deposition (MOCVD) system. A variety of structural and electrical characterizations were routinely used to provide fast feedback for adjusting growth parameters and developing improved growth processes.