In situ optical monitoring of AlGaN thickness and composition during MOVPEgrowth of AlGaN/GaN microwave HFETs

Real-time spectral reflectometry has been implemented to monitor the MOVPE growth of AlGaN/GaN microwave HFET structures. The aim is to monitor and co ntrol the thickness and composition of the thin AlGaN layer during growth. In order to extract useful information from the in situ spectra the optical constants of AlGaN as a function of alloy composition are required at the growth temperature (similar to 1050 degreesC). As the first step to obtaini ng the high temperature optical constants, a room temperature spectroscopic ellipsometry study (energy range 1.65-4.95 eV) has been carried out on thi n AlGaN films of various thickness (30 and 100 nm) and aluminium content (0 .15 and 0.25). The multilayer model of each sample from the ellipsometry st udy is used to generate a reflectance spectrum which is compared with the i n situ spectral reflectometry spectrum of the same sample acquired at room temperature to verify the technique. Further work is in progress to model t he bandgap and optical constants of GaN and AlGaN at growth temperature. Cr own Copyright (C) 2001 Published by Elsevier Science B.V. All rights reserv ed.