Ray Li

1200-V Normally Off GaN-on-Si Field-Effect Transistors With Low Dynamic on -Resistance

This letter reports high-voltage GaN field-effect transistors fabricated on Si substrates. A halide-based plasma treatment was performed to enable normally off operation. Atomic layer deposition of Al2O3 gate insulator was adopted to reduce the gate leakage current. Incorporation of multiple field plates, with one field plate connected to the gate electrode and two field plates connected to the source electrode successfully enabled a high breakdown voltage of 1200 V and low dynamic on-resistance at high-voltage operation.

High-voltage vertical GaN Schottky diode enabled by low-carbon metal-organic chemical vapor deposition growth

Vertical GaN Schottky barrier diode (SBD) structures were grown by metal-organic chemical vapor deposition on free-standing GaN substrates. The carbon doping effect on SBD performance was studied by adjusting the growth conditions and spanning the carbon doping concentration between ≤3 × 1015 cm−3 and 3 × 1019 cm−3. Using the optimized growth conditions that resulted in the lowest carbon incorporation, a vertical GaN SBD with a 6-μm drift layer was fabricated. A low turn-on voltage of 0.77 V with a breakdown voltage over 800 V was obtained from the device.

An Experimental Demonstration of GaN CMOS Technology

This letter reports the first demonstration of gallium nitride (GaN) complementary metal-oxide-semi-conductor (CMOS) field-effect-transistor technology. Selective area epitaxy was employed to have both GaN N-channel MOSFET (NMOS) and P-channel MOSFET (PMOS) structures on the same wafer. An AlN/SiN dielectric stack grown by metal-organic chemical vapor deposition served as the gate oxide for both NMOS and PMOS, yielding enhancement-mode N- and P-channel with the electron mobility of 300 cm2/V-s and hole mobility of 20 cm2/V-s, respectively. Using the GaN CMOS technology, a functional inverter integrated circuit was fabricated and characterized.

600 V/

This letter reports a GaN vertical trench metal-oxide-semiconductor field-effect transistor (MOSFET) with normally-off operation. Selective area regrowth of n±GaN source layer was performed to avoid plasma etch damage to the p-GaN body contact region. A metal-organic-chemicalvapor-deposition (MOCVD) grown AlN/SiN dielectric stack was employed as the gate “oxide”. This unique process yielded a 0.5-mm2-active-area transistor with threshold voltage of 4.8 V, blocking voltage of 600 V at gate bias of 0 V, and on-resistance of 1.7 Ω at gate bias of 10 V.

1.7~\Omega

Power switches based on GaN-on-Si transistor technology have the advantage of high switching speed and low fabrication cost. This paper reports our recent advancement in device technology which enabled nanosecond switching at one kilowatt, with an unprecedented slew rate of 325 V/ns. The high switching speed opens up pathways for emerging applications such as envelope tracking and wireless power charging.

Normally-Off GaN Vertical Trench Metal–Oxide–Semiconductor Field-Effect Transistor

We report a GaN-on-Si metal-insulator-semiconductor field-effect transistor (MISFET) with normally-off operation and 600-V blocking capability at 200 °C temperature. The temperature-dependences of threshold voltage, on-resistance, and leakage characteristics are discussed.

Normally-Off GaN-on-Si transistors enabling nanosecond power switching at one kilowatt

In a vertical GaN Schottky barrier diode, the free electron concentration n in the 6-μm-thick drift layer was found to greatly impact the diode reverse leakage current, which increased from 2.1 × 10−7 A to 3.9 × 10−4 A as n increased from 7.5 × 1014 cm−3 to 6.3 × 1015 cm−3 at a reverse bias of 100 V. By capping the drift layer with an ultrathin 5-nm graded AlGaN layer, reverse leakage was reduced by more than three orders of magnitude with the same n in the drift layer. We attribute this to the increased Schottky barrier height with the AlGaN at the surface. Meanwhile, the polarization field within the graded AlGaN effectively shortened the depletion depth, which led to the formation of tunneling current at a relatively small forward bias. The turn-on voltage in the vertical Schottky diodes was reduced from 0.77 V to 0.67 V—an advantage in reducing conduction loss in power switching applications.

Normally-off GaN-on-Si metal-insulator-semiconductor field-effect transistor with 600-V blocking capability at 200 °C

Two critical processes within the gate module of GaN-based MOS-HEMT with significant impact on device robustness and performance were identified and are presented in this paper. Specifically, data highlighting the impact of the number of cycles of the atomic layer etching of the AlGaN barrier to recess the gate region and the sequence of the gate dielectric anneal step on device performance are discussed. The optimization of these two critical steps enabled the implementation of a 50A/600V with an off-state leakage current of 455 μA at 600V and on-state resistance of 41mΩ at VGS=2.5V.

Improved performance in vertical GaN Schottky diode assisted by AlGaN tunneling barrier

The main driving force for High Operating Temperature (HOT) detectors is the strong need for low cost, compact IR imaging solution capable of supporting a wide range of military and civilian applications. In the HOT regime where imagers can be cooled with multi-stage thermoelectric coolers, the major portion of the cost is due to the die-level back-end process, from the chip hybridization to final packaging. We present here an approach to achieve significant cost reduction of MWIR imagers by monolithically integrating III-V devices directly on Silicon substrates for wafer-scale fabrication and packaging of focal plane arrays (FPAs). High quality InAs films can be grown on a blanket Silicon wafer by metal-organic chemical vapor deposition (MOCVD) in a low growth temperature regime that complies with the thermal budget of the Si-electronics. High Resolution Transmission Electron Microscopy reveals predominantly oriented, single-crystal-like InAs films, with Σ3(111) twin boundaries, which our band structure calculations predict to be electrically benign. More intriguingly, selective-area growth on SiO2-masked ROIC-like templates is demonstrated with single-crystal-like InAs film nucleation at small Si(001) openings, together with the suppression of unwanted deposition on the dielectric mask. High crystallinity lateral epitaxial overgrowth of the InAs islands and film coalescence is achieved, enabling the potential to fully cover the entire patterned substrate. MBE-grown MWIR devices (λcut-off = 4.1 μm) on blanket InAs/Si templates exhibit a dark current of 2x10-5 A/cm2 , a specific detectivity of 6x1011 Jones and a quantum efficiency (QE) above 60% at 100K. The QE remains constant at high temperatures (<200K) where the dark current approaches that of baseline single-crystal HOT devices grown on native substrates At 230K, it is 6x10-2 A/cm2, yielding a specific detectivity of 1010 Jones.

Critical gate module process enabling the implementation of a 50A/600V AlGaN/GaN MOS-HEMT

Vertical GaN power semiconductors promise higher power with faster switching speeds but the development of this technology has been slowed. This is due to the expense and lack of familiarity with GaN substrates. This paper will detail the functionality of HRLs cutting-edge vertical GaN transistor which is mounted onto a specially made PCB and tested. The testing consists of a static characterization which shows a breakdown voltage of 600 V, as well as the transfer characteristics, output characteristics, and the on-state resistance with respect to current. The device is then switched at various voltages and currents with voltage switching speeds up to 97 V/ns. The device is successfully switched up to 450 V under a 2 A load current.