New process approaches to metalorganic vapor phase epitaxy of III-nitrides for high power HEMTs
type: CreativeWork
description: As a promising candidate for future microwave power devices, GaN-based high-electron mobility transistors (HEMTs) have attracted much research interest. However, group III-nitride growth related issues – predominantly the high defect densities due to lacking lattice matched substrates – limit the quality and life time of the HEMTs. In the AlGaN/GaN heterostructure the GaN buffer layer is particularly important for that matter. Several requirements need to be satisfied, such as high buffer resistivity, low dislocation densities and smooth and defect free interfaces. Poor reproducibility and uniformity of the heterostructure is an additional challenge. Research aim of this work is to develop a MOVPE based growth process that allows the reliable and efficient deposition of high quality material for HEMT devices based on AlGaN/GaN heterojunctions on sapphire substrates. Usage and development of adequate growth control and monitoring instruments is essential to meet these premises. Direct wafer surface temperature determination is a must during growth, though it is challenging for transparent substrates. A new calibration method is demonstrated that uses the in-situ measured, temperature dependent band-gap shift of SiC. This technique allows adjusting any MOVPE system to identical run-by-run wafer temperatures. Using this new temperature determination approach the cause of irreproducibility in an horizontal reactor is investigated. The two major origins of irreproducibility are parasitic deposits that form on the cold reactor walls which allow for insufficient temperature control. Thus, a new deposition approach is introduced that reduces the formation of parasitic depositions, by injecting the metalorganics near the substrate unlike the conventional process. Experiment and modelling verify the suitability of the new growth approach for enhanced reproducibility. The new approach leads to a fourfold reactor uptime. The structural, morphological and electrical characterist…
abstract: As a promising candidate for future microwave power devices, GaN-based high-electron mobility transistors (HEMTs) have attracted much research interest. However, group III-nitride growth related issues – predominantly the high defect densities due to lacking lattice matched substrates – limit the quality and life time of the HEMTs. In the AlGaN/GaN heterostructure the GaN buffer layer is particularly important for that matter. Several requirements need to be satisfied, such as high buffer resistivity, low dislocation densities and smooth and defect free interfaces. Poor reproducibility and uniformity of the heterostructure is an additional challenge. Research aim of this work is to develop a MOVPE based growth process that allows the reliable and efficient deposition of high quality material for HEMT devices based on AlGaN/GaN heterojunctions on sapphire substrates. Usage and development of adequate growth control and monitoring instruments is essential to meet these premises. Direct wafer surface temperature determination is a must during growth, though it is challenging for transparent substrates. A new calibration method is demonstrated that uses the in-situ measured, temperature dependent band-gap shift of SiC. This technique allows adjusting any MOVPE system to identical run-by-run wafer temperatures. Using this new temperature determination approach the cause of irreproducibility in an horizontal reactor is investigated. The two major origins of irreproducibility are parasitic deposits that form on the cold reactor walls which allow for insufficient temperature control. Thus, a new deposition approach is introduced that reduces the formation of parasitic depositions, by injecting the metalorganics near the substrate unlike the conventional process. Experiment and modelling verify the suitability of the new growth approach for enhanced reproducibility. The new approach leads to a fourfold reactor uptime. The structural, morphological and electrical characterist…
author: Steins, Roger
language: eng
keywords: info:eu-repo/classification/ddc/620, Ingenieurwissenschaften, MOCVD-Verfahren, Wide-gap-Halbleiter, Heterostruktur, Nitride, Pyrometrie, HEMT, GaN, MOVPE, III-nitrides, in-stu reflectometry
date published: 2006
date modified: 2026-07-30T19:43:10Z
provider: RWTH Aachen University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Publikationsserver der RWTH Aachen University