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AlGaN/GaN high-electron-mobility transistors (HEMTs) with postpassivation plasma treatment are demonstrated and investigated for the first time. The results show that postpassivation plasma treatment can reduce the gate leakage and enhance the drain current. Comparing with the conventional devices, the gate leakage of AlGaN/GaN HEMTs with postpassivation plasma decreases greatly while the drain current increases. Capacitance–voltage measurement and frequency-dependent conductance method are used to study the surface and interface traps. The mechanism analysis indicates that the surface traps in the access region can be reduced by postpassivation plasma treatment and thus suppress the effect of virtual gate, which can explain the improvement of DC characteristics of devices. Moreover, the density and time constant of interface traps under the gate are extracted and analyzed. [ABSTRACT FROM AUTHOR]

Nonalloyed ohmic contacts regrown by metal-organic chemical vapor deposition are performed on AlGaN/GaN high-electron-mobility transistors. Low ohmic contact resistance of 0.15ω·mm is obtained. It is found that the sidewall obliquity near the regrown interface induced by the plasma dry etching has great influence on the total contact resistance. The fabricated device with a 100-nm T-shaped gate demonstrates a maximum drain current density of 0.95 A/mm at Vgs = 1 V and a maximum peak extrinsic transcondutance Gm of 216 mS/mm. Moreover, a current gain cut-off frequency fT of 115 GHz and a maximum oscillation frequency fmax of 127 GHz are achieved. [ABSTRACT FROM AUTHOR]

In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field (PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility. Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness. This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect. [ABSTRACT FROM AUTHOR]

Microplasmas have attracted more and more attention due to their unique characteristics, and breakdown voltage is an important parameter for microplasma devices, particularly for addressable arrays of microplasma devices. However, small changes in shape or interface would bring obvious change in breakdown voltage. In this paper, five groups of simulations of breakdown voltage were operated under different geometry parameters to develop the trend of breakdown voltage following geometrical size under different operation pressures. The drift–diffusion approximation model is adopted in these simulations. The simulation results show that breakdown voltage will increase with the increase in the microcavity depth and thickness of the dielectric. Therefore, the breakdown voltage will reduce when microcavity width increases. The less is the microcavity size, the less is breakdown voltage, and the higher is the pressure corresponding to minimum breakdown voltage, which shows that the decrease in microcavity size can develop operation pressure and decrease breakdown voltage obviously. [ABSTRACT FROM PUBLISHER]

The electron mobility of the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with the ratio of the gate length to the drain-to-source distance being less than 1/2 has been studied in the temperature range 100 300 K. The measured electron mobility at each testing temperature is obtained by using the capacitance-voltage ( C- V) and current-voltage ( I- V) characteristics measured at the corresponding temperature, and the theoretically calculated temperature-dependent electron mobility is determined by Matthiessen's law, which includes five kinds of important scattering mechanisms. For the prepared sample, the measured electron mobility with respect to the two-dimensional electron gas (2DEG) density was observed to increase to a peak point first and then decrease at each testing temperature. By comparing the measured electron mobility with the theoretically calculated value, the changing trend of the electron mobility at each testing temperature was found to be mainly determined by polarization Coulomb field (PCF) scattering. Particularly at lower temperature, PCF scattering plays a more significant role in the changing trend of the electron mobility. [ABSTRACT FROM AUTHOR]

A simple and effective approach to improve the switching characteristics of AlGaN/AlN/GaN heterostructure field effect transistors (HFETs) by applying a voltage bias on the substrate is presented. With the increase of the substrate bias, the OFF-state drain current is much reduced and the ON-state current keeps constant. Both the ON/OFF current ratio and the subthreshold swing are demonstrated to be greatly improved. With the thinned substrate, the improvement of the switching characteristics with the substrate bias is found to be even greater. The above improvements of the switching characteristics are attributed to the interaction between the substrate bias induced electrical field and the bulk traps in the GaN buffer layer, which reduces the conductivity of the GaN buffer layer. [ABSTRACT FROM AUTHOR]

Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N-polar GaN, the Al metal in Ohmic stacks is found to react with background oxygen more easily, resulting in more AlOx. In addition, the formation of AlOx is affected by the Al layer thickness greatly. The AlOx combined with the presence of AlN is detrimental to the Ohmic contacts for N-polar GaN compared with Ga-polar GaN. With the reduction of the Al layer thickness to some extent, less AlOx and AlN are formed, and lower Ohmic contact resistance is obtained. The lowest contact resistivity ρ of 1.97 × 10−6 Ω·cm2 is achieved with the Al layer thickness of 80 nm. [ABSTRACT FROM AUTHOR]

We report on the temperature-dependent dc performance of AlGaN/GaN polarization doped field effect transistors (PolFETs). The rough decrements of drain current and transconductance with the operation temperature are observed. Compared with the conventional HFETs, the drain current drop of the PolFET is smaller. The transconductance drop of PolFETs at different gate biases shows different temperature dependences. From the aspect of the unique carrier behaviors of graded AlGaN/GaN heterostructure, we propose a quasi-multi-channel model to investigate the physics behind the temperature-dependent performance of AlGaN/GaN PolFETs. [ABSTRACT FROM AUTHOR]