IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Tuesday Sessions
       Session SC-TuM

Paper SC-TuM8
Metal-Induced States and Polytype Transformations at SiC Interfaces

Tuesday, October 30, 2001, 10:40 am, Room 124

Session: Semiconductor Interfaces and Thin Films
Presenter: S.P. Tumakha, Ohio State University
Authors: S.P. Tumakha, Ohio State University
L.J. Brillson, Ohio State University
G.H. Jessen, Ohio State University
R.S. Okojie, NASA-Glenn Research Center
D. Lukco, NASA-Glenn Research Center
Correspondent: Click to Email
We have used low energy electron-excited nanoluminescence (LEEN) spectroscopy to probe electronic structure at chemically-treated and metallized 4H and 6H-SiC interfaces. SiC high temperature electronics requires metal contacts with controllable barriers and minimal deep level electronic states. LEEN spectra over incident electron beam energies E from 0.5 to 5 keV identify the presence of localized states and their spatial distribution on a nanometer scale. With increasing E, the electron cascade and resultant generation of free electron-hole pairs peak at increasing depth ranging from 10 nm at 0.5 keV to 200 nm at 5 keV. The resultant band-to-band and band-to-defect luminescence is detected selectively at the intimate metal-SiC interface, the near-interface region extending tens of nanometers into the SiC, or the bulk SiC up to 0.2 microns into the solid. Pt/Ti/SiC junctions were prepared by standard cleaning, oxidation, and etching methods. 6H-SiC exhibits optical emission that varies with depth from the intimate interface and with surface chemical preparation. The depth-dependent spectra exhibit 2.9 eV near band edge (NBE) features of 6H-SiC for bulk excitation vs. a disordered and/or defected region within a few nm of the metal contact. Spectra from the near interface region indicate the existence of a SiC polytype with a higher band gap of ca 3.4 eV - resembling 4H-SiC as well as a discrete deep level, i.e., emission energy = 1.9 eV, for a specific surface treatment. Metal-induced features on 4H-SiC are similar. In addition, oxidation before or after metallization produces 2.5 eV emission extending hundreds of nm into the 4H bulk, characteristic of polytype conversion to 3C-SiC and confirmed by TEM. A strong impurity doping dependence suggests that oxidation or metallization-induced strain drives this transformation. The structural as well as electronic changes at SiC interfaces have significant device and processing implications.