No abstract

We have demonstrated Si implantation incorporation into GaN HEMTs with a non-alloyed ohmic contact process. We optimized the power density of pulsed laser annealing to activate implanted Si dopants without a thermal metallization process. The experimental results show that the GaN surface will be reformed under the high power density of the illumination conditions. It provides a smooth surface for following contact engineering and leads to comparable contact resistance. The transmission line model (TLM) measurement shows a lower contact resistance to 6.8×10 −7 Ω•cm 2 via non-alloyed contact technology with significantly improved surface morphology of the contact metals. DC measurement of HEMTs shows better current and onresistance. The on-resistance could be decreased from 2.18 to 1.74 mΩ-cm 2 as we produce a lower contact resistance. Pulsed laser annealing also results in lower gate leakage and smaller dispersion under a pulse I-V measurement, which implies that the density of the surface state is improved.

This paper reports the successful fabrication of a GaN-on-Si high electron mobility transistor (HEMT) with a 1702 V breakdown voltage (BV) and low current collapse. The strain and threading dislocation density were well-controlled by 100 pairs of AlN/GaN superlattice buffer layers. Relative to the carbon-doped GaN spacer layer, we grew the AlGaN back barrier layer at a high temperature, resulting in a low carbon-doping concentration. The high-bandgap AlGaN provided an effective barrier for blocking leakage from the channel to substrate, leading to a BV comparable to the ordinary carbon-doped GaN HEMTs. In addition, the AlGaN back barrier showed a low dispersion of transiently pulsed I D under substrate bias, implying that the buffer traps were effectively suppressed. Therefore, we obtained a low-dynamic on-resistance with this AlGaN back barrier. These two approaches of high BV with low current collapse improved the device performance, yielding a device that is reliable in power device applications.

Over the last five decades, there has been a decline of rural communities in Taiwan due to urbanization expansion. In the past 10 years, the central government has implemented the Rural Regeneration Project (RRP) aimed at revitalization and sustainable development in rural Taiwan. During the project’s implementation, communities have faced several disasters as a result of climate change-induced extreme rainfall events. Perceptions and adaptation practices of climate change-induced extreme events are critical to community sustainability and resilience. The gap between perceived and actual risks that communities experience creates challenges for policy-makers in achieving sustainability goals. This study aims to evaluate the perceived climate change-induced flooding hazard perceptions compared to the scientific projection and actual hazard events in 287 rural communities implementing the RRP. This study revealed consistency in risk perception, in that communities facing high potential exposure to extreme rainfall showed higher awareness of various impacts of climate change. However, when comparing climate actions, communities exposed to low-potential hazard areas had a relatively higher degree of recognition of the benefits of adaptation to climate change. Moreover, 59 rural communities with low awareness and exposed to high potentials of extreme events were widely distributed among hills of western, southern, and northern Taiwan, where compound disasters such as mudslides can occur. This research suggests that there is a need to integrate climate change planning and work with communities to bridge the gap between perceived and actual climate risks. In particular, capacity training, counseling services, and implementation of adaptation practices should be integrated into institutional planning and management for providing assistance in disaster prevention, relief, and post-event restoration; also, encouraging climate actions can directly improve community resilience toward climate change. While investing in the sustainable development of rural communities is largely based on revitalizing economic development, this study revealed the link to ensure resilience and social-ecological sustainability in rural communities under climate change impacts.

Novel nanometer T-gate process has been developed utilizing electron beam (EB) lithography and thermally reflowed resist technique. Through well-controlled EB exposure dosage, heating time and reflow temperature, the resist structures can be efficiently reflowed to form the desired T-gate configuration with dimension ranging from 150 nm to 30 nm. After Ti/Pt/Au metal deposition by electron gun evaporation and lift-off process, the nanometer T-gates with thickness of about 500 nm were formed. With the optimized conditions, ultra-short 30 nm T-shaped gate was clearly demonstrated on the GaAs substrate. This is the smallest T-gate reported with the thermally reflowed technique in the literature so far and can practically be used in the GaAs monolithic microwave integrated circuit (MMIC) fabrications.