The semiconductor gallium arsenide (GaAs) has many potential advantages over the more widely used semiconductor silicon (Si). These include higher low field mobility, semi-insulating substrates, a direct band-gap, and greater radiation hardness. All these advantages offer distinct opportunities for implementation of new circuit functions or extension of the operating conditions of similar circuits in silicon based technology. However, full exploitation of these advantages has not been realized. This study examines the limitations imposed on conventional GaAs metal-semiconductor field effect transistor (MESFET) technology by deviations of the semi-insulating substrate material from ideal behavior. The interaction of the active device with defects in the semi-insulating GaAs substrate is examined and the resulting deviations in MESFET performance from ideal behavior are analyzed. A p-well MESFET technology is successfully implemented which acts to shield the active device from defects in the substrate. Improvements in the operating characteristics include elimination of drain current transients with long time constants, elimination of the frequency dependence of g[subscript ds] at low frequencies, and the elimination of sidegating. These results demonstrate that control of the channel to substrate junction results in a dramatic improvement in the functionality of the GaAs MESFET. The p-well MESFET RF characteristics are examined for different p-well doping levels. Performance comparable with the conventional GaAs MESFET technology is demonstrated. Results indicate that optimization of the p-well MESFET doping levels will result in devices with uniform characteristics from DC to the highest operating frequency. / Graduation date: 1991

A complete Gallium Arsenide Metal Semiconconductor Field Effect Transistor (GaAs MESFET) model including deep-level trap effects has been developed, which is far more accurate than previous equivalent circuit models, for high-speed applications in linear integrated circuit design. A new self-backgating GaAs MESFET model, which can simulate low frequency anomalies, is presented by including deep-level trap effects which cause transconductance reduction and the output conductance and the saturation drain current to increase with the applied signal frequency. This model has been incorporated into PSPICE and includes a time dependent I-V curve model, a capacitance model, a subthreshold current model, an RC network describing the effective substrate-induced capacitance and resistance, and a switching resistance providing device symmetry. An analytical approach is used to derive capacitances which depend on Vgs and Vds and is one which also includes the channel/substrate junction modulation by the self backgating effect. A subthreshold current model is analytically derived by the mobile charge density from the parabolic potential distribution in the cut-off region. Sparameter errors between previous models and measured data in conventional GaAs MESFET's have been reduced by including a transit time delay in the transconductances, gm and gds, by the second order Bessel polynomial approximation. As a convenient extraction method, a new circuit configuration is also proposed for extracting simulated S-parameters which accurately predict measured data. Also, a large-signal GaAs MESFET model for performing nonlinear microwave circuit simulations is described. As a linear IC design vehicle for demonstrating the utility of the model, a 3-stage GaAs operational amplifier has been designed and also has been fabricated with results of a 35 dB open-loop gain at high frequencies and a 4 GHz gain bandwidth product by a conventional half micron MESFET technology. Using this new model, the low frequency anomalies of the GaAs amplifier such as a gain roll-off, a phase notch, and an output current lag are more accurately predicted than with any other previous model. This new self-backgating GaAs MESFET model, which provides accurate voltage dependent capacitances, frequency dependent output conductance, and transit time delay dependent transconductances, can be used to simulate low frequency effects in GaAs linear integrated circuit design. / Graduation date: 1991

Originally presented as the author's thesis (Swiss Federal Institute of Technology), Diss. ETH No. 13547. / Summary in German and English. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 89-95). Available also in a digital version from Dissertation Abstracts.

Not available / text

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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