Near-interface traps in n-type SiO 2 /SiC MOS capacitors from energy-resolved CCDLTS
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1246-B09-02
Near-interface traps in n-type SiO2/SiC MOS capacitors from energy-resolved CCDLTS Alberto F. Basile1, Sarit Dhar2,a, John Rozen2,b, Xudong Chen1,c, John R. Williams3, Leonard C. Feldman2,4, and Patricia M. Mooney1 1 Department of Physics, Simon Fraser University, Burnaby, BC V5A 1S6, Canada 2 Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA 3 Department of Physics, Auburn University, Auburn, AL 36849, USA 4 Institute of Advanced Materials, Devices and Nanotechnology, Rutgers University, Piscataway, NJ 08854, USA
ABSTRACT Silicon Carbide (SiC) Metal-Oxide-Semiconductor (MOS) capacitors, having different nitridation times, were characterized by means of Constant Capacitance Deep Level Transient Spectroscopy (CCDLTS). Electron emission was investigated with respect to the temperature dependence of emission rates and the amplitude of the signal as a function of the filling voltage. The comparison between the emission activation energies of the dominant CCDLTS peaks and the filling voltages, led to the conclusion that the dominant trapping behavior originates in the Silicon-dioxide (SiO2) layer. Moreover, a model of electron capture via tunneling can explain the dependence of the CCDLTS signal on increasing filling voltage. INTRODUCTION The channel electron mobility in SiC Metal-Oxide-Semiconductor Field-Effect-transistors (MOSFETs) is a fundamental parameter that determines device performance. Even after many years of research, the effective channel mobility remains more than an order of magnitude lower than the electron mobility in bulk SiC [1]. The comparison between SiO2/SiC interfaces fabricated on different SiC polytypes led to a preliminary understanding of the energy distribution of traps at the oxide-semiconductor interface [2]. The channel mobility was shown to be strongly dependent on the energy gap of the semiconductor, being significantly lower in MOSFETs on the larger band-gap 4H-SiC polytype. The slight reduction in the band-gap energy (EG) from 3.23eV in 4H-SiC down to 3.0eV in 6H-SiC, is accompanied by an increase in channel mobility from barely measurable values in 4H-SiC up to 30cm2/(V·s) in 6H-SiC. The latter, however, is far below the bulk mobility of 300 cm2/(V·s) in 6H-SiC. This observation suggested the presence of a high density of interface states energetically close to the 4H-SiC conduction band energy (EC), but resonant with EC in 6H-SiC. The mobility increase in 4H-SiC to values typical of 6H-SiC, recently achieved by means of post-oxidation annealing in NO gas [3], represents a technological breakthrough and also offers an opportunity to study the nature of these traps [4]. a
Present address: Power Electronics R&D, Cree Inc., Durham, NC 27703, USA Present address: Central Research Institute of Electric Power Industry, Yokosuka, Kanagawa 240-0196, Japan c Present address: Redlen Technologies, Sidney, BC V8L 5Y8, Canada b
The trapping properties at the SiO2/4H-SiC interface in as-oxidized samples have been experimentally characterized by se
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