Xun Dong

Monolithic Integration of E/D-Mode AlGaN/GaN MIS-HEMTs

Monolithic integration of enhancement/depletion (E/D)-mode AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) are demonstrated for mixed signal applications. The gate length for the E-mode and D-mode devices are 0.2 μm and 0.35 μm, respectively, and drain current of 496 (Vgs=+5 V) and 720 mA/mm (Vgs=0 V) with a peak transconductance of 147 and 131 mS/mm are measured. Small-signal measurements result matched current-gain cutoff frequency (fT)/maximum oscillation frequency (fmax) of 29.9/55.2 GHz for the E-mode and 27.5/47.5 GHz for the D-mode devices. Direct-coupled FET logic E/D MIS-HEMT inverter and 51-stage ring oscillator are fabricated. The incorporation of gate dielectric enables the inverter a large logic voltage swing of 3.71 V at a supply voltage VDD of 5 V. The 51-stage ring oscillator implemented with 106 transistors shows an oscillation frequency of 427.6 MHz at VDD=5 V, corresponding to a stage delay of 23 ps.

Monolithic integrated enhancement/depletion-mode AlGaN/GaN high electron mobility transistors with cap layer engineering

Monolithic integrated enhancement/depletion (E/D)-mode AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated on an AlGaN/GaN heterostructure with an engineered triple-cap-layer. The energy band of the cap layer is greatly tailored by the polarizations within it, which improves the controllability of D-to-E mode conversion with gate recess. The uniformity of the threshold voltage (Vth) across a 3″ wafer is assessed and the standard deviations of Vth are 0.1 V and 0.14 V for E-mode and D-mode devices, respectively. Direct-coupled field-effect transistor logic E/D HEMT inverter and 17-stage ring oscillator are demonstrated, and the latter shows a oscillation frequency of 201 MHz at a supply voltage of 1 V, corresponding to a propagation delay of 146 ps/stage and a power-delay product of 1.96 pJ/stage.

Identifying Interface States in AlInN/GaN Heterostructure by Photocurrent Method

In order to assess the residual leakage current mechanisms in electronic devices based on AlInN/GaN heterostructures, defect states were investigated by photocurrent method based on a metal-semiconductor-metal structure device. As a result, a continuous distribution of defect levels from 56 to 110 meV below the conduction band of GaN was identified at the AlInN/GaN interface by analyzing photocurrent spectra under different bias voltages and photogenerated carrier transport based on the simulation of electric field distribution. These interface states filled with electrons at zero bias can release electrons at reverse bias and provide a path of gate leakage.

Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr0.52Ti0.48)-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (gm-Vg) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectric constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric.

Dual-gate AlGaN/GaN MIS-HEMTs using Si3N4 as the gate dielectric

We have investigated dual-gate AlGaN/GaN metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) using Si3N4 as the gate dielectric by comparison with single-gate MIS-HEMTs. It is shown that the presence of the second gate induces a slight reduction in the maximum output current, transconductance and breakdown voltage, but with the advantages of 5 dB enhanced power gain and higher f T/f max. Combined with a physics-based device simulation, the breakdown characteristics of the dual-gate device are revealed to be dependent on the second gate. These results demonstrate that the incorporation of dual-gate configuration into the MIS gate is a potential alternative for GaN-based high-power and high-frequency applications.

A 0.15µm gate InAlN/GaN HEMT with thin barrier layer

High quality thin barrier layer In0.18Al0.82N/GaN heterostructure was grown by metal-organic chemical vapor deposition (MOCVD). A 0.15 μm gate InAlN/GaN HEMT was fabricated with 1A/mm drain current at zero gate bias. The device show good pinch-off performance. A high transconductance of 482 mS/mm and current gain cutoff frequency of 80GHz were measured without de-embedding.

Two-terminal electroluminescence of AlGaN/GaN high electron mobility transistors

Electroluminescence (EL) characteristics from reverse-biased Schottky barrier diode are investigated on AlGaN/GaN high electron mobility transistors (HEMT) with different structures. Light emission from devices under high voltage or with high gate leakage current exhibit bluish or reddish color, suggesting different emission mechanism. No obvious EL is observed in AlGaN/GaN/AlGaN double heterostructure at high drain voltage near breakdown. 2D device simulation of the AlGaN/GaN HEMT at high drain voltage shows distinct separation of electrons and holes distribution, eliminating the possibility of direct band-to-band transitions. By comparing the EL image from front side and back side of the wafer, the manufacturing related problems as well as the location of material defects are detected.

InAlN/AlN/GaN HEMTs on sapphire substrate

High quality InAlN/AlN/GaN heterostructure is grown by metal organic chemical deposition (MOCVD) on sapphire substrate. A high two-dimensional electron gas (2DEG) density of 2.5×1013 cm−2 was measured in this structure. To character the electric property of this heterostructure, a 1-μm-long gate InAlN/AlN/GaN high-electron mobility transistors (HEMTs) were fabricated. A maximum output current density of 1.19 A/mm and a peak extrinsic transconductance of 240 mS/mm were measured with the InAlN/AlN/GaN HEMTs. Compare to the normal AlGaN/AlN/GaN HEMTs, the maximum current density and transconductance is greatly improved due to the high 2DEG density and thin barrier layer.