Optimization of the Field Plate Design of a 1200 V p-GaN Power High-Electron-Mobility Transistor.

This study optimized the field plate (FP) design (i.e., the number and positions of FP layers) of p-GaN power high-electron-mobility transistors (HEMTs) on the basic of simulations conducted using the technology computer-aided design software of Silvaco. Devices with zero, two, and three FP layers were designed. The FP layers of the HEMTs dispersed the electric field between the gate and drain regions. The device with two FP layers exhibited a high off-state breakdown voltage of 1549 V because of the long distance between its first FP layer and the channel. The devices were subjected to high-temperature reverse bias and high-temperature gate bias measurements to examine their characteristics, which satisfied the reliability specifications of JEDEC.

Characteristic Analysis of AlGaN/GaN HEMT with Composited Buffer Layer on High-Heat Dissipation Poly-AlN Substrates.

In this study, an AlGaN/GaN high-electron-mobility transistor (HEMT) was grown through metal organic chemical vapor deposition on a Qromis Substrate Technology (QST). The GaN on the QST device exhibited a superior heat dissipation performance to the GaN on a Si device because of the higher thermal conductivity of the QST substrate. Thermal imaging analysis indicated that the temperature variation of the GaN on the QST device was 4.5 °C and that of the GaN on the Si device was 9.2 °C at a drain-to-source current (IDS) of 300 mA/mm following 50 s of operation. Compared with the GaN HEMT on the Si device, the GaN on the QST device exhibited a lower IDS degradation at high temperatures (17.5% at 400 K). The QST substrate is suitable for employment in different temperature environments because of its high thermal stability.

Badland landscape response to individual geomorphic events.

Landscapes form by the erosion and deposition of sediment, driven by tectonic and climatic forcing. The principal geomorphic processes of badland - landsliding, debris flow and runoff erosion - are similar to those in full scale mountain topography, but operate faster. Here, we show that in the badlands of SW Taiwan, individual rainfall events cause quantifiable landscape change, distinct for the type of rainfall. Typhoon rain reduced hillslope gradients, while lower-intensity precipitation either steepened or flattened the landscape, depending on its initial topography. The steep topography observed in our first survey is inconsistent with the effects of any of the rainfall events. We suggest that it is due to the 2016 Mw 6.4 Meinong earthquake. The observed pattern in the badlands was mirrored in the response of the Taiwan mountain topography to typhoon Morakot in 2009, confirming that badlands offer special opportunities to quantify natural landscape dynamics on observational time scales.

Solid-State Carbon-Doped GaN Schottky Diodes by Controlling Dissociation of the Graphene Interlayer with a Sputtered AlN Capping Layer.

Carbon-doped GaN (GaN:C) Schottky diodes are prepared by controlling the destruction status of the graphene interlayer (GI) on the substrate. The GI without a sputtered AlN capping layer (CL) was destroyed because of ammonia precursor etching behavior in a high-temperature epitaxy. The damaged GI, like nanographite as a solid-state carbon doping source, incorporated the epitaxial growth of the GaN layer. The secondary ion mass spectroscopy depth profile indicated that the carbon content in the GaN layer can be tuned further by optimizing the sputtering temperature of AlN CL because of the better capping ability of high crystalline quality AlN CL on GI being achieved at higher temperature. The edge-type threading dislocation density and carbon concentration of the GaN:C layer with an embedded 550 °C-grown AlN CL on a GI substrate can be significantly reduced to 2.28 × 109 cm-2 and ∼2.88 × 1018 cm-3, respectively. Thus, a Ni-based Schottky diode with an ideality factor of 1.5 and a barrier height of 0.72 eV was realized on GaN:C. The series resistance increased from 28 kΩ at 303 K to 113 kΩ at 473 K, while the positive temperature coefficient (PTC) of series resistance was ascribed to the carbon doping that induced the compensation effect and lattice scattering effect. The decrease of the donor concentration was confirmed by temperature-dependent capacitance-voltage (C-V-T) measurement. The PTC characteristic of GaN:C Schottky diodes created by dissociating the GI as a carbon doping source should allow for the future use of high-voltage Schottky diodes in parallel, especially in high-temperature environments.