Ž . Diamond and Related Materials 10 2001 12831286 Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC K. Bertilsson a,b,  , E. Dubaric a,b , H-E. Nilsson a , M. Hjelm a,b , C.S. Petersson b a Department of Information Technology, Mid-Sweden Uni  ersity, S-851 70 Sunds  all, Sweden b ( ) Department of Solid State Electronics, Kungl. Tekniska Hogskolan KTH , Electrum, S-164 40 Kista, Sweden ¨ Abstract Ž . Ž The 4H-SiC static induction transistor SIT is a very competitive device for high frequency and high power applications 3  6 . GHz range . The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device.  2001 Elsevier Science B.V. All rights reserved. Ž . Keywords: Device modeling; Metal semiconductor field effect transistors MESFET ; 4H-SiC; 6H-SiC 1. Introduction High-speed SiC devices are today dominated by MESFET transistors for low power and SIT transistors  for high-power electronics 1 . State of the art tech- nology have until now reported SiC MESFETs devices operating with a unity current gain frequency, f  22 T   GHz 2 and SITs with f  7 GHz 3 . T Ž . The SIT vertical MESFET device is already today an interesting high frequency device. Fabricated MES- FETs are faster, but the superior power capabilities of the SIT devices give a promising future for high-speed, high-power electronics.  Corresponding author. Tel.: 46-60-14-89-15; fax: 46-60-14- 88-30. Ž . E-mail address: kent.bertilsson@ite.mh.se K. Bertilsson . The difference between the two structures is schematically presented in Fig. 1. The vertical MES- FET is a device with periodic symmetry and gate fingers at both sides surrounding the channel. The dual-gate operation results in approximately twice the transcon- ductance and cut-off frequency as a MESFET of equal size. The higher transconductance is owing to the dou- ble side depletion of the channel, requiring smaller signal amplitude of V for the same amplitude of I . gs ds A vertical MESFET permits a shorter channel com- pared to a lateral MESFET, since the channel length is defined by the gate metal thickness instead of the Ž . length. The drain-source length L is set by the DS epitaxial layer thickness, and the lithography limits the channel width. A short device with a wide channel is difficult to deplete; the channel length can thus not be decreased to a length significantly shorter than channel 0925-963501$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 9 2 5 - 9 6 3 5 00 00382-4