Design criteria for GaAs MESFETs related to stationary high field domains

Using a modified theory of the high-field domains which takes into account the field-dependent diffusion we show that the existence of the high-field domain at drain side of the gate in GaAs MESFETs leads to a new set of design criteria which should be met to achieve the optimum performance. We derive these criteria and estimate the drain-to-source breakdown voltage and the maximum power of the device as functions of the doping density and device dimension. We also estimate the optimum gate length, the thickness of the active layer, the drain-to-gate separation and the doping level as functions of frequency. It is demonstrated that a larger than conventional drain-to-gate separation might be necessary for power devices to house a fully developed highfield domain and to avoid a premature breakdown at the drain. Our estimates indicate that the maximum power at 10 GHz can reach a theoretical limit of about 20 watts for class A operation.     

Composition and submicron structure of thin films of supersaturated Zn x Pb1 − x S solid solutions

Thin films of supersaturated Zn _x Pb_{1 ? x} S solid solutions containing up to 4.1 mol % ZnS have been obtained by hydrochemical deposition. The dependence of the material structure and surface morphology on the film composition has been studied. It is established that an increase in the content of zinc sulfide leads to the growth of grains with a more complicated crystalline structure, the formation of grain boundary fragments with dimensions from 60 to 100 nm, and a modification of the electrical properties of deposited layers.     

Dynamic current-voltage characteristics of III-N HFETs

A comparative study of the dynamic current-voltage (DI-V) characteristics of III-N heterojunction and double heterojunction field-effect transistors (HFETs and DHFETs) reveals that the current and RF power collapse in HFETs arise from modulation of device series resistances under large input signal. A model based on space-charge limited current through the depletion regions formed at the gate edges due to the charge trapping explains the DI-V behavior and other observations related to the RF current collapse in III-N HFETs.     

SiO/sub 2//AlGaN/InGaN/GaN MOSDHFETs

The characteristics of a novel nitride based field-effect transistor combining SiO/sub 2/ gate isolation and an AlGaN/InGaN/GaN double heterostructure design (MOSDHFET) are reported. The double heterostructure design with InGaN channel layer significantly improves confinement of the two-dimensional (2-D) electron gas and compensates strain modulation in AlGaN barrier resulting from the gate voltage modulations. These decrease the total trapped charge and hence the current collapse. The combination of the SiO/sub 2/ gate isolation and improved carrier confinement/strain management results in current collapse free MOSDHFET devices with gate leakage currents about four orders of magnitude lower than those of conventional Schottky gate HFETs.