Jia-Ching Lin

Improved Output Power of Nitride-Based Light-Emitting Diodes With Convex-Patterned Sapphire Substrates

Nitride-based light-emitting diodes (LEDs) grown on different convex-patterned sapphire substrates are proposed and fabricated. The electrical and optical properties of these LEDs are discussed in detail. It is found that the LED with a ball-shape patterned sapphire substrate has the best crystalline quality and I-V characteristic. On the other hand, on reducing total internal reflection, the LED with hexagonal-shape patterned sapphire substrate (HPSS) has the best performance on output power and external quantum efficiency. In comparison to the LED without patterned substrate, the LED with HPSS has 175% and 165% enhancement on output power and external quantum efficiency, respectively.

Photocatalytic study of zinc oxide with different bismuth doping

The zinc oxides (ZnO) films with different bismuth (Bi) doping were prepared by spray pyrolysis deposition at 450°C with aqueous solution contained zinc acetate and bismuth nitrate precursors. Under ultra-violate light illumination, the photodegradation of methyl orange for these ZnO films were studied. In the singly doped ZnO, the 5% Bi doped ZnO shows the relatively high photocatalytic activity. The reaction rate was achieved and possible reason was discussed. It is found that the raction rate can be enhanced by increasing the surface doping. The absorption coefficient was investigated and possible reason was discussed.

Temperature dependency and reliability of through substrate via InAlN/GaN high electron mobility transistors as determined using low frequency noise measurement

The reliability of a InAlN/GaN/Si high electron mobility transistor device was studied using low frequency noise measurements under various stress conditions. By applying the through substrate via (TSV) technology beneath the active region of the device, buffer/transition layer trapping caused by the GaN/Si lattice mismatch was suppressed. In addition, a backside SiO2/Al heat sink material improved thermal stability and eliminated the vertical leakage current of the proposed device. Applying the TSV technology improved the subthreshold swing slope from 260 to 230 mV/dec, owing to the stronger channel modulation ability and reduced leakage current of the device. The latticed-matched InAlN/GaN heterostructure had a stable performance after high current operation stress. The suppression of buffer/transition layer traps of the TSV device is a dominant factor in device reliability after long-term high-electric-field stress.

Modeling of Fatigue for Cellular Materials

Dimensional arguments are used to analyze the fatigue of cellular materials. A modeling describing the fatigue of foams with or without macrocrack is derived and compared to the existing experimental data of cementitious foams and phenolic foams; agreement is good.

Normally-off matrix layout p-GaN gate AlGaN/GaN power HEMT with a through-substrate via process

Normally-off p-GaN gate AlGaN/GaN high electron mobility transistor (HEMT) on Si substrate with matrix heat redistribution layer (RDL) and through substrate via (TSV) technologies was investigated. Compared to traditional power cell design, the modified matrix heat RDL provides a circular arc layout together with an extra drain pad to reduce rectangular layout induced leakage current and the device total current density was also enhanced. In addition, TSV process beneath the GaN power HEMT active region spreads the heat efficiently and the lattice mismatch induced traps in transition/buffer layer were also removed. Based on the measured results analysis of dynamic RON to DC RON (RDC), the removal of lossy substrate in TSV is also beneficial for improving device switching behavior. Therefore, a high switching speed normally-off GaN power HEMTs together with a superior thermal management was proposed in this study.

Investigation of the (Cu,Ga)InSe2 thin film with different pairs of CuGa/In sputtered layers

Thin film samples of (Cu,Ga)InSe2 (CIGS) were prepared by DC magnetron sputtering and the selenisation process onto soda lime glass substrates. All samples had the same deposition conditions, and the optimal sputtering thickness of samples with one CuGa/In pair and two CuGa/In pairs are also the same. After sample deposition, X-ray diffraction (XRD), scanning electron microscope (SEM) and Hall effect measurements were used to characterize the properties of these samples. From XRD measurement results, excepting an extra small CuSe peak existing in the samples with two CuGa/In pairs, the XRD peaks of all samples are perfectly matched with the phase diagram of CuGa0.3In0.7Se2 material. It was also found that the grain sizes of the samples with one CuGa/In pair are larger than those with two CuGa/In pairs from SEM images. All these observations on samples with two CuGa/In pairs can be attributed to the fact that the less In incorporation in CIGS films, which it has been proven that the sample with low In-to-CuGa ratio has stronger CuSe peak from XRD result. Furthermore, the p-type carrier characteristics can be observed for all samples from Hall measurement results. The carrier mobility and concentration of the samples with one CuGa/In pair can be achieved as high as 15.28 cm2/Vs and as low as 1.50×1016 cm-3, respectively, while the carrier mobility and concentration of the ones with two CuGa/In pairs can be achieved as 6.4 cm2/Vs and 6.27×1017 cm-3, respectively. The results of superior electrical properties of samples with one CuGa/In pair agree well with the observations form XRD and SEM results. In the final, the optimal value of In-to-CuGa ratio during CuGa/In layers deposition in this study is 0.625.

High electron mobility AlGaN/AlN/GaN HEMT structure with a nano-scale AlN interlayer

Epitaxies of AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with different thickness of nano-scale AlN interlayers have been realized by metalorganic chemical vapor deposition (MOCVD) technology. After epitaxy, high resolution X-ray diffraction (HRXRD), temperature-dependent Hall Effect and atomic force microscopy (AFM) measurements were used to characterize the properties of these samples. First, it was found that the Al composition of AlGaN layer increases from 21.6 to 34.2% with increasing the thickness of AlN interlayer from 0 to 5 nm under the same AlGaN growth conditions. This result may due to the influences of compressive stress and Al incorporation induced by the AlN interlayer. Then, we also found that the room-temperature (RT) electron mobility stays higher than 1500 cm2/Vs in the samples within AlN interlayer thickness range of 1.5 nm, on the other hand, the low-temperature (80K) electron mobility drops dramatically from 8180 to 5720 cm2/Vs in the samples with AlN interlayer thickness increasing from 1 to 1.5 nm. Furthermore, it was found that the two-dimensional electron gas (2DEG) density increases from 1.15×1013 to 1.58×1013 cm-2 beyond the AlN interlayer thickness of 1 nm. It was also found that the temperature independent 2DEG densities are observed in the samples with AlN interlayer thickness of 0.5 and 1 nm. The degenerated characteristics of the samples with AlN thickness thicker than 1.5 nm show the degraded crystalline quality which matched the observation of surface defects and small cracks formations from their AFM images. Finally, the 2DEG mobilities of the proposed structures can be achieved as high as 1705 and 8180 cm2/Vs at RT and 80K, respectively.