Modeling Techniques of Submicron GaAs MESFETs and HEMTs

Abstract

This thesis discusses the electrical response of submicron GaAs MESFETs and HEMTs to develop a physical model. Nine different FET models have been presented and their ability to simulate submicron GaAs MESFET characteristics are checked. To demonstrate the validity of a model, I-V characteristics of short channel MESFETs are simulated and compared with experimental data. The accuracy of a model is reported by evaluating its RMS error values. A comprehensive new model is developed to simulate I-V characteristics of short channel GaAa FETs. It has been demonstrated that the proposed model is a comprehensive one, capable of simulating DC characteristics of GaAs MESFETs including those having significant non-ideal Schottky barrier response. The model has also been applied successfully to I-V characteristics of GaAs HEMTs. The Schottky barrier interfacial layer dependent performance of submicron GaAs MESFETs has been discussed by using their output and transfer characteristics. The mobility of carriers, scattering from the channel into the Schottky barrier gate, increases significantly for the devices which have a relatively thicker interfacial layer. The negative effects of increased carriers’ mobility from MESFET Schottky barrier gate are discussed and a plausible explanation is given for reduced barrier lowering in the presence of interfacial layer. Based on the proposed explanation the definition of threshold voltage has been redefined involving the concept of interfacial layer thickness. A technique is developed to estimate intrinsic small signal parameters of GaAs MESFETs and HEMTs. In the proposed technique DC characteristics are first evaluated. Once a good DC match is attained then small signal parameters are evaluated. To check the validity of the proposed technique submicron GaAs MESFETs and HEMTs of varying gate length have been simulated. It has been shown that the proposed method is accurate as well as efficient in estimating AC parameters of GaAs FETs by using their DC characteristics, and could be employed as a useful tool in device simulation software.