Full Band Monte Carlo Simulation of Short Channel MOSFETs in 4H and 6H-SiC
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PETERSSON IDepartment of Information Technology, Mid-Sweden University, S-851 70 Sundsvall, Sweden, [email protected] 2 Department of Solid State Electronics, Kungl. Tekniska Hbgskolan (KTH), Elektrum 229, S-164 40 Kista, Sweden 3 Department of Physics and Measurement Technology, Linkiping University, S-581 83 Linktping, Sweden 4 lnstitut fUr Festkbrpertheorie und Theoretische Optik, Max-Wien-Platz 1, 07743 Jena, Germany
ABSTRACT This is a presentation of a full band Monte Carlo (MC) study, which compares electron transport and device performance for 4H and 6H-SiC 100 nm n-channel MOSFETs. The model used for the electrons is based on data from a full potential band structure calculation using the Local Density Approximation (LDA) to the Density Functional Theory (DFT). For the holes the transport is based on a three band k-p model including spin orbit interaction. The two polytypes are compared regarding surface mobilities obtained with the program, as well as transconductance, unit current gain frequency, carrier velocity, I-V characteristics and energy distribution in the channel for the MOSFETs.
INTRODUCTION Silicon carbide (SIC) is considered to be a very promising material for high temperature and high power applications due to its high breakdown voltage and high thermal conductivity. One possibility is the fabrication of high speed integrated MOSFETs in 4H-SiC on a semi-insulating substrate, with the expectation of a reliable and stable operation. An advantage for both 4H-SiC and 6H-SiC is their discontinuous energy spectrum in the conduction band along the c-axis direction, which results in limited carrier heating by the electric field. Another factor tending to lower
the carrier energy is the strong polar optical scattering. CMOS integrated circuits have been fabricated on 6H-SiC [1,2], showing that commercial SiC MOSFETs will be available in the near future. This paper presents a comparison, using a full band Monte Carlo model, of 4H-SiC and 6HSiC regarding the surface mobility and device properties in short channel MOSFETs.
MONTE CARLO MODEL The full band MC program is based on a large lookup table, stored for the irreducible part of the Brillouin zone and containing the energy and energy gradient versus k-vector from the band structure. Between the points represented in the lookup table, the energy values are calculated using a second order cubic spline, and the energy gradient by linear interpolation. The band data in the simulations presented here are based on the calculations in reference [3] and reference [4]. The following scattering processes are considered: acoustic phonon scattering, polar optical phonon scattering, zero and first order optical intervalley phonon scattering and ionised impurity scattering [5,6]. For the acoustic and optical phonons, the coupling constants are obtained by fitting data from bulk simulations to experimental data from references [7] and [8]. As a result the transport properties in the simulations correspond to those in the material used in the referred experim
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