Analysis and improvement of mm-wave GaAs MESFET's

A two-dimensional computer model, which takes into account the nonstationary conditions, is used to investigate several aspects of the GaAs submicron-gate MESFET. First, this model is used to evaluate the effects of carrier injection into the MESFET buffer-layer. It is shown that the carrier of injection reduces the transconductance and increases the output conductance. One of the ways to reduce the carrier injection is to introduce a potential-barrier between the active-layer and the substrate. Therefore, the MESFET grown on a P-substrate is studied. It is shown that a high acceptor concentration in the substrate depletes large part of the active-layer and greatly reduces the output current. A more flexible design can be obtained by introducing a thin P-layer between the active-layer and the semi-insulating substrate. This model is also used in investigating the traveling Gunn domain phenomenon in GaAs MESFETs. It is shown that traveling domains exist in MESFETs with relatively thick active-layers. The propagation characteristics of these domains are studied in detail. A new structure called Inverted-Gate FET (INGFET) is studied as well. This structure has equal input and output reactances. Hence, it relaxes the restriction on the device width which becomes very severe in the mm-wave range. Another structure that employs carrier injection over a N + i junction and possesses equal input and output reactances is analyzed. It is called Inverted-Gate-Injection FET (INGIFET).