Gallium arsenide floated electron channel field effect transistor

Abstract

In this dissertation, a new GaAs field effect transistor is proposed and fabricated by using selective metal organic chamical vapor deposition(S-MOCVD). The new device is named as Floated Electron Channel Field Effect Transistor(FECFET) because the active channel is separated from the semi-insulating substrate. In order to achieve a novel device structure with very short channel length, the facet shapes dependence on the growth conditions of S-MOCVD is basically used. The lateral growth parameters for the device design are characterized and modeled using the atomic arrangement. From the dc measurement of the fabricated FECFET, it is confirmed that the device has a few advantages as follows. The high transconductance is obtained by achieving the short channel geometry, which is resulted form the carrier saturation velocity enhancement or the velocity overshoot effect. Because the thick n$^+$-layer for source and drain ohmic contacts are separated by a small distance under the gate, the source and the drain resistance are significantly reduced. A low output conductance is also achieved by eliminating the current path flowing through the buffer layer. It is also demonstrated that the device has negligible side-gate effect and the threshold voltage of the device can be controlled by both the recess depth and the mask size. When the device is measured at the microwave frequency range, the current gain cutoff frequency is higher than that of the conventional MESFET at the same gate dimension. As an example, a 1.3$\mu$m-gate FECFET had a current gain cutoff frequency of 19GHz and a maximum oscillation frequency of about 40GHz. Using the small signal equivalent circuit topology of the conventional MESFET``s, the parameters of the fabricated devices are extracted based on the measured s-parameters. From the analysis of the extracted circuit parameters, it is found that one of the most effective circuit parameters is the gate to drain capacitance. The noise properties of...