This work reports effects of excited surface states on off current (IOFF) of AlGaN/GaN high electron mobility transistor (HEMT). A detailed mechanism of IOFF increase under white light illumination is studied, emphasizing the role of surface states present on the GaN capping layer. The increase in surface potential under white light illumination and elevated temperatures lead to a decrease in depletion region width. This decrease causes an increased leakage of electrons from source to drain in GaN buffer by reducing punch-through voltage which leads to an increase in IOFF. Left shift in threshold voltage with an increase in intensity of light is also observed which indicates the threshold voltage instability that white light or high temperatures can cause in the device.

This letter reports electrical properties of Al-GaN/GaN high electron mobility transistor (HEMT) with epitaxial Nd2O3 as a gate insulator. The introduction of Nd2O3 between metal and semiconductor in the gate region, results in two orders of magnitude reduction of gate leakage current, which remains unchanged even at higher temperature of 200°C. The Ion/I off also remains constant at 200°C and the transconductance stays at its peak over a significant range of gate bias (4.5 V). This linearity is attributed to the increased electron concentration in channel due to introduction of epitaxial Nd2O3 and the resulting strain on AlGaN barrier layer. The increased 2DEG density also leads to an increase in output drain current from the metal oxide semiconductor(MOS)-HEMT.

This work reports NbN as a schottky gate on AlGaN/GaN high electron mobility transistor (HEMT). We observed a significant reduction of gate leakage current and three order of magnitude improvement in ON/OFF ratio for NbN gated HEMT as compared to that of Ni/Au gated control HEMT sample. We measured an enhancement of transconductance (maximum) in case of NbN HEMT (85 mS/mm) as compared to control sample (78 mS/mm). The all nitride-HEMT also exhibits the better thermal stability at higher temperatures ( 200°C). The subthreshold slope is also seen to decrease from 266 mV/decade for Ni/Au MSHEMT to 72 mV/decade for NbN MSHEMT. Lastly, our study confirms that the use of NbN as a gate could significantly improve the performance of all-nitride AlGaN/GaN HEMT with better threshold voltage stability and reduced hysteresis in transfer characteristics as compared to the conventional metal gated HEMT.