Characterization of Gallium-Arsenide Mesfets Fabricated Using Ion-Beam Etching Technology.

The use of ion-beam etching for the controllable formation of very thin active channel layers in GaAs MESFETs is investigated and compared with chemical and plasma etching techniques. The Schottky gate diodes associated with ion-beam-etched surfaces show significant surface damage, a substantial part of which can be removed by annealing. Typical annealed diodes exhibit a barrier height of 0.53 eV and an ideality factor of 1.22. The optimal annealing conditions have been found to be at 400(DEGREES)C for about 2.5 minutes. A modified Schottky theory is presented which includes the effects of surface states and a thin interfacial layer between the metal and semiconductor. This model appears to account for most of the observed behavior. For submicron gate-length MESFETs, the transconductance begins to decrease when the gate bias approaches zero. The occurrence of this current crowding phenomenon depends on the process, the gate metal, and the dimension of the gate. A model is proposed which considers the depletion region under the free surface in a MESFET. This model appears to be able to explain this phenomenon qualitatively very well. A modified MESFET model including the current crowding effect is developed. A channel capacitance term is used to account for the intrinsic delay. The calculated results of this model are compared with the measured MESFET step-response and published two-dimensional device simulations. Good agreement has been obtained. A simple temperature model is also presented and is shown to be accurate by comparing the simulation results with measurements. Utilizing the MESFET model and the network simulation program 'MACMOD', several examples of circuit design are demonstrated.PhDElectrical engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159154/1/8304462.pd