Phonons on Quantum Epitaxial Structures Based on Wide Band Gap Materials

Abstract

Public «port™ burden for ihii collection of erlormetion a estmatad to average 1 hour per response, including the lime lor warning «struct«™, searching ousting data sources, gathermf| ancminting the data needed, and comple rng arc1 rtirwmng the collection of «formation. Sand commtnti regarding thii burden tatimate or any other aspect of this eduction of mlormalion. «eroding suggestions for raducing this burden, to Washington Headquarters Seros. Dmioraie to-imormation Operations and Reports. 1215 Jefferson Dans rughway. Suite 1204. Arlington. VA 222024302, and to the Office of Management and Budget. Paperwork Reduction Project 10704-0188), Washington, DC 20503. AGENCY USE ONLY (Leave blank)2. REPORT DATE 30 December 1998 REPORT TYPE AND DATES COVERED FINAL March 1997-31 August 2000 TITLE AND SUBTITLE Phonons on Quantum Epitaxial Structures Based on Wide Band Gap Materials AUTHORIS) Mitra Dutta PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)North Carolina State University, Raleigh, NC 27695-8202 SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)U SUPPLEMENTARY NOTESThe views, opinions and/or finding contained in this report are those of the author(s) and should not be construed as an official Department of Army position, policy of decision, unless so designated buy other documentation. 12a. DISTRIBUTION AVAILABILITY STATEMENTApproved for public release; distribution unlimited. 12b. DISTRIBUTION CODE ABSTRACT (Maximum 200 words/Raman scattering studies were performed on III-V Nitride materials including binary crystals, ternary alloys, and superlattices of GaN/AIN and GaN/AlGaN. Our results show that in AlGaN alloys the asymmetric behavior of the E21ineshape arises from random disorder; the E2 phonon does not follow a one mode behavior and the AlGaN films on SiC are under small tensile stress. In the InGaN too the Al mode shows a one mode behavior while two mode behavior may be possible for E2. Possible mode mixing takes place. Evidence of inhomogeneities and spinodal decomposition is seen in these films. Phonon lifetime measurements are made in the binary crystals and in every case we see evidence of two lifetime regions. In the superlattices we see anomalous low temperature behavior that is consistent with a density of states of spectral distribution that is due to the roughness of the interfaces and which agrees with TEM measurements. Finally preliminary measurements demonstrate strong interface phonons in the GaN/AIN superlattices which give good agreement with theory. SUBJECT TERMSWide band gap semiconductors, phonons and their lifetimes. NUMBER OF PAGES 087 Phonons on Quantum Epitaxial Structures Based on Wide Band Gap Materials PrefaceRaman scattering studies were performed on III-V Nitride materials including binary crystals, ternary alloys, and superlattices of GaN/AIN and GaN/AlGaN. Our results show that in AlGaN alloys the asymmetric behavior of the E21ineshape arises from random disorder; the E2 phonon does not follow a one mode behavior and the AlGaN films on SiC are under small tensile stress. In...