2-D simulation of GaAs MESFET''s

• Main Authors: Wang, Yo-Jen, 王佑仁
• Other Authors: Lu Shey-Shi
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/99452823973850032026

博士 === 國立臺灣大學 === 電機工程學系研究所 === 86 === Abstract: Two-dimensional simulation of GaAs MESFET''s was presented in this thesis. GaAs MESFET''s have the advantage of having higher speed than Si devices have, so they have been widely used in high-speed applications especially today in wireless communications. Ion-implanted planar gate power MESFET (no recess etching) is suitable for the power amplifier in cellular phones in dual mode operation because it has high efficiency and linearity in the digital mode and good efficiency in the analog mode. However, because the power MESFET is always biased at near pinch-off region for low power consumption, the behavior of the device near pinch-off is very critical for the performance of the amplifier. The most significant phenomena of the MESFET near pinch-off is the substrate leakage. One way to eliminate the substrate leakage is to implant p-type ion (Be) to form a p-type buffer under the channel. Too low Be dose is not sufficient to prevent the substrate leakage, yet too high dose will reduce the saturation current and the breakdown voltage. With the help of two-dimensional simulation, the optimal design of the ion- implanted power mesfet was obtained. Furthermore, V-groove gate MESFET''s were simulated and an interesting mechanism of short channel effect we named the Drain-Induced Carrier Accumulation (DICA) effect was first found. An analytical model for the V-groove gate MESFET was proposed. The model fitted the simulation results very well and it has meaningful parameters. The substrate effects for the V-groove MESFET were simulated also. The devices with three substrates, the undoped GaAs , the undoped AlGaAs and the p- doped substrate, were simulated. For the one with the undoped GaAs substrate, substrate leakage was found; the device with the undoped AlGaAs, DICA effect; and the device with the p-doped substrate, both the substrate leakage and the DICA effect occurred. In addition, ultra-high frequency V-gate MESFET was first proposed to have ft up to 47 Ghz in the optimal condition by 2-D simulation. The device has submicron gate length without resorting to expensive E-beam lithography and delicate multilayer of photoresist. It may be very useful for microwave amplifier in the future.