Chunhong Zeng

Enhancement-Mode Operation of Nanochannel Array (NCA) AlGaN/GaN HEMTs

In this letter, enhancement-mode (E-mode) AlGaN/ GaN high electron mobility transistors (HEMTs) were demon- strated based on lateral scaling of the 2-D electron gas channel using nanochannel array (NCA) structure. The NCA structure consists of multiple parallel channels with nanoscale width defined by electron-beam lithography and dry etching. Because of the improved gate control from the channel sidewalls and partially relaxed piezoelectric polarization, the fabricated 2 μm-gate-length NCA-HEMT with a nanochannel width of 64 nm showed a thresh- old voltage of +0.6 V and a higher extrinsic transconductance of 123 mS/mm, compared to -1.6 V and 106 mS/mm for the conventional HEMT with μm-scale channel width. The scaling of threshold voltages, peak transconductance, and gate leakage as a function of the nanochannel width were investigated. Small-signal RF performance of NCA-HEMTs were characterized for the first time and compared with those of conventional HEMTs.

Room temperature GaN/AlGaN self-mixing terahertz detector enhanced by resonant antennas

This letter focuses on the fabrication and characterization of a terahertz detector integrated with a group of low pass filters and resonant antennas. The detector operates as a self-mixer on GaN/AlGaN high electron mobility transistor (HEMT). At room temperature, a strong dc photocurrent is produced with the aid of the antennas and filters. The responsivity of our HEMT device is estimated to be 53 mA/W and a noise equivalent power of 1 nW/Hz can be achieved at 300 K. In addition, the sensor properties of a similar HEMT detector without filter are tested as a comparison.

Dynamic Characterizations of AlGaN/GaN HEMTs With Field Plates Using a Double-Gate Structure

A novel double-gate AlGaN/GaN HEMT, in which an additional top-gate covers the adjacent regions of a normal gate, was proposed and fabricated for the first time to compare the dynamic characteristics of AlGaN/GaN HEMTs with a source field plate (SFP) and a gate field plate (GFP). During the dynamic characterization, the device was configured in two operation modes: One is the SFP mode with the top gate biased at 0 V, and the other is the GFP mode applying the gate pulse signal on the top gate at the same time. Compared with an AlGaN/GaN HEMT without field plates, both GFP and SFP much improve the dynamic performances. Compared with the SFP, the GFP shows better dynamic performances with a ~ 34% reduction of switch-on delay time and ~ 6% reduction of dynamic on-state resistance. Studying the dynamic characteristics and applying negative voltage on the top gate during the off state, the mechanism differences between the GFP and the SFP are discussed in detail.

Enhanced Device Performance of AlGaN/GaN High Electron Mobility Transistors with Thermal Oxidation Treatment

We systematically investigated the effect of the thermal oxidation treatment on the performance of AlGaN/GaN high electron mobility transistors (HEMTs). The HEMTs with thermal oxidation treatment exhibit four orders of magnitude reduction in gate leakage current, 80% reduction of trap density, and more than two times improvement of off-state drain breakdown voltage, compared with those shown by HEMTs without thermal oxidation treatment. The simplicity in the thermal oxidation treatment process, coupled with the drastic improvement in device performance render the thermal oxidation treatment highly promising for GaN-based microwave power amplifier applications in communication and radar systems.

A Double-Gate AlGaN/GaN HEMT With Improved Dynamic Performance

In this letter, a double-gate AlGaN/GaN high electron mobility transistor operated in a synchronized switching mode is demonstrated, and improved dynamic performances are obtained. The additional gate sits on top of the conventional gate and stretches 2/4 μm to the source/drain electrodes, respectively. A positive voltage pulse is applied to the top gate and is synchronized with the ON-OFF switching pulse applied to the conventional gate. Such a double-gate driving method significantly improves the dynamic performances of the device. Moreover, it allows us to investigate the dynamic on-resistance in the drift region in detail.

Influences of ICP etching damages on the electronic properties of metal field plate 4H-SiC Schottky diodes

Inductively coupled plasma (ICP) etching of 4H-SiC using SF 6 /O 2 gas mixture was studied systematically and the effect of etching was examined by metal field plate SiC Schottky diodes (SBDs).It was found that the etch rate as well as SiC surface morphology were related with ICP power, RF power, pressure, the flow of SF 6 and O 2 .Etching damages (the cone-in-pits and pits) generated at high chuck self-bias were observed, and they were thought to be caused by SiC defects.The degradation of both the reverse and forward I-V performances of SiC SBDs was ascribed to the cone-in-pits and pits.Moreover, the absolute value of forward current is even less than the reverse counterpart in the absolute value voltage range of 0-50 V for SiC SBDs with etching damages.