We report on the frequency dependent conductance measurements of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). The properties of the devices with as-deposited and annealed 9-nm-thick Al2O3 gate oxide were investigated. The trap density in the range of 1011 cm−2 eV−1 was evaluated for the nonannealed devices. However, the conductance versus frequency peaks were significantly broader than those expected from theory, which indicates a surface potential fluctuation due to nonuniformities in the oxide charge and interface traps. Additionally, the dependence of the trap state time constant on gate voltage showed a deviation from the expected exponential function. However, the annealed devices (680 °C, 5 min) yielded a slightly lower (∼75%) trap density. Moreover, the conductance versus frequency data and the time constant versus gate voltage dependence of the annealed devices were in full agreement with the theoretical ones. The results show that the frequency dependent conductance analysis can be a useful tool for the characterization of AlGaN/GaN MOSHFETs.

No abstract

The authors report on improved transport properties of Al2O3∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). It is found that the drift mobility in the MOSHFET structures with 4nm thick Al2O3 gate oxide is significantly higher than that in HFETs. The zero-bias mobilities are 1950 and 1630cm2∕Vs for the MOSHFET and HFET, respectively. An ∼40% increase of the saturation drain current in the MOSHFETs compared to the HFETs seems to be larger than expected from the passivation effects. The MOSHFET devices show a higher transconductance (with peak values of ∼115mS∕mm) than the HFETs (∼70mS∕mm). Analysis of the device performance indicates a decrease of the parasitic series resistance together with an enhancement of the effective velocity of the channel electrons in the MOSHFET devices.