AVS 52nd International Symposium
    Electronic Materials and Processing Monday Sessions
       Session EM+NS-MoM

Paper EM+NS-MoM10
Optical and Ellipsometric Studies on InN Layers Grown by High-Pressure CVD

Monday, October 31, 2005, 11:20 am, Room 310

Session: Novel Approaches in Wide Bandgap Semiconductors
Presenter: N. Dietz, Georgia State University
Authors: N. Dietz, Georgia State University
M. Alevli, Georgia State University
M. Strassburg, Georgia State University
V.T. Woods, Georgia State University
U. Perera, Georgia State University
N.A. Stoute, North Carolina State University
D.E. Aspnes, North Carolina State University
Correspondent: Click to Email
The fabrication of emerging detector and emitter structures as well as high-frequency/high-power devices operating at high temperature(s) that are based on group III-nitride compound alloys is presently limited by the challenging difficulties in the growth of high quality In-rich group-III-nitride alloys and heterostructures. Even though recent improvements in MBE-grown InN material established a band gap near 0.65 eV, other data show a band gap near 1.85 eV. The origin of this bandgap difference is not understood. Here, we focus on the analysis of optical data obtained both by absorption spectroscopy and spectroscopic ellipsometry (SE) on InN material grown by high-pressure chemical vapor deposition (HPCVD) in the 10 to 15 bar pressure range as a function of growth temperature, flow rate, and flow ratios of ammonia and trimethylindium (TMI). With HPCVD we can compensate the inherent volatility of nitrogen and stabilize indium-rich conditions and grow group-III-nitride alloys at temperatures comparable to those used for GaN and AlN. The optical data indicate that the decrease in optical absorption edge from 1.85 eV to 0.63 eV is caused by a series of absorption centers appearing at 1.6 eV, 1.35 eV, 1 eV, 0.87 eV and below 0.65 eV. The appearance of these centers correlates with the indium-to-nitrogen ratio, which is controlled through the flow rates of ammonia and TMI. For InN layers grown near 1100 K and molar ammonia/TMI ratios less than 200, an InN absorption edge below 0.63 eV is observed. For material with absorption edges near 1.9 eV a strong peak is observed, which appears to be excitonic in nature.