The radio-frequency characteristics of insulated submicron-gate III-N heterostructure field-effect transistors

This dissertation describes large-signal radio-frequency (rf) performance of novel III-N Insulated Gate Heterostructure Field-Effect Transistors (IGHFETs), with particular focus on submicron gate design. It demonstrates that the suppression of the gate leakage currents in the IGHFETs results in the overall improved rf device performance as compared to the conventional Schottky-gate HFETs.; Unique properties of GaN-based devices, such as high electron mobility and saturation velocity, high sheet carrier concentration at heterojunction interfaces, high breakdown field, and low thermal impedance (when grown over SiC or bulk AlN substrates) make them extremely promising for high-power high-temperature applications. An AlGaN/GaN Heterostructure Field Effect Transistor (HFET) is one of the most promising electronic devices, which has been a topic of intensive investigations since the first report in 1991. The III-N based HFET can deliver the rf powers as high as 10W/mm, which is about 10 times higher than those of GaAs based devices. However, the HFET high-power performance is limited by high gate leakage currents. Novel Insulated Gate HFET design resolves this problem by introducing thin dielectric layer between the gate and the channel, which reduces the gate current by several orders of magnitude. The combination of insulated gate design and submicron gate geometry should result in further improvement in the power gain and operation frequencies. However, the rf performance parameters of the submicron gate IGHFETs, have not been studied before. This dissertation presents for the first time the detailed study of small- and large-signal rf characteristics of the IGHFETs. We show both experimentally and theoretically that for the III-N IGHFETs, such key performance parameters as the cut-off frequencies, power gain and power added efficiency are the same as for conventional HFETs, whereas the saturation power, large-signal linearity and rf power stability are superior.