Numerical analysis of formation properties of a high-field dipole domain for submicron GaAs field-effect transistor devices

Abstract

A typical 0.3-μm gate-length submicron GaAs metal-semiconductor field-effect transistor (MESFET) is simulated using a complete energy model that solves a complete form of the energy conservation equation, and also using a simplified energy model that only neglects heat flux for electrons. The simulations are carried out with the same device physical and bias conditions, and a transient analysis is made to investigate thermal electron conduction effects on the formation property of a high-field dipole domain in the submicron GaAs MESFET. It is shown that the simplified model leads to the existence of a very unstable Gunn domain oscillating between the gate and drain, but the more accurate complete model gives a stable high-field domain confined well in the gate region due to thermal electron conduction. The crucial reason for this discrepancy between the two results is associated with the capable limits of accuracy in the simplified model. That is, this model gives rise to an unduly large retardation in the energy-gaining rate of electrons in the gate channel, so that the production of the negative differential resistance phenomenon by the electrons is largely delayed under the gate. Therefore, a traveling Gunn domain can be exhibited for submicron GaAs field-effect transistors in the simulation by a simplified energy model. It is demonstrated that even though simplified energy models are capable of reflecting the nonstationary effect of velocity overshoot properly, it is quite improper to apply these for studying device physics related to dipole domain properties; thermal electron conduction plays a pivotal role in forming a stable dipole domain in the submicron GaAs MESFET. In addition, the average effective valley-transition force for channel electrons (a new physical quantity first defined in the paper) is used to show that simplified energy models give a much larger magnitude for the force (approximately 1.8 eV/μm) compared to 1.2 eV/μm given by the complete energy model. Furthermore, the force is given closer to the drain end of the gate in the former models. Therefore, simplified energy models have a high possibility of creating a traveling domain for submicron devices.