Shu-Cheng Chang

Use of patterned laser liftoff process and electroplating nickel layer for the fabrication of vertical-structured GaN-based light-emitting diodes

The fabrication process and performance characteristics of a vertical-structured GaN-based light-emitting diode (VM-LED) employing nickel electroplating and patterned laser liftoff techniques are presented. As compared to regular LED, the forward voltage drop of the VM-LED at 20–80 mA is about 10%–21% lower, while the light output power (Lop) is more than twice in magnitude. Especially, the Lop exhibits no saturation or degradation at an injection current up to 520 mA which is about 4.3 times higher than that of the regular one. Substantial improvements in the VM-LEDs performances are mainly attributed to the use of metallic substrate which results in less current crowding, larger effective area, and higher thermal conductivity.

Growth and characterization of tungsten carbide nanowires by thermal annealing of sputter-deposited WCx films

In this letter, the growth of dense W2C nanowires by a simple thermal annealing of sputter-deposited WCx films in nitrogen ambient is reported. Straight nanowires with a density of 250–260μm−2 and length∕diameter in the range of 0.2–0.3μm∕13–15nm were obtained from the 700°C-annealed samples, which exhibit good electron field emission characteristics with a typical turn-on field of about 1.7V∕μm. The self-catalytic growth of W2C nanowires is attributed to the formation of α-W2C phase caused by carbon depletion in the WCx films during thermal annealing.

High-Power GaN-Based Light-Emitting Diodes with Transparent Indium Zinc Oxide Films

Large-area (0.6 mm×0.6 mm–1.5 mm×1.5 mm), high-power GaN-based blue-light-emitting diodes (LEDs) with an indium zinc oxide (IZO) overlay as a transparent conduction layer (TCL) and the effects of the overlayer on light output power (Lop) improvement are investigated. Experimental results show that sputter-deposited IZO TCLs with thicknesses in the range of 100–500 nm have a low resistivity ranging from 12.1–3.1×10-4 Ω-cm and a transparency ≥80% in the visible light range. The benefit obtained from the use of an IZO TCL is much more profound in LEDs of larger chip size; in addition, the optimum IZO TCL thickness is approximately 300 nm. As compared to the case without an IZO layer, under an injection current of 60–1000 mA, a 39–90% improvement in Lop has been achieved from LEDs (1.5 mm×1.5 mm) with a 300-nm-thick IZO TCL.

A vertical-structured Ni/GaN schottky barrier diode using electroplating nickel substrate

In this work, a vertical-structured Ni/u-GaN (2 µm)/n-GaN (1.5 µm) Schottky barrier diodes (SBDs) employing an electroplating nickel substrate and laser lift-off processes is proposed and experimental results are reported. A metal system comprising a Ti/Al/Ti/Au mutilayer structure was used to form ohmic contact to n-GaN. A specific contact resistance as low as 6.64×10-5 Ωcm2 has been obtained after sample thermal annealing in Ar ambient at 800 °C for 30 s. A KOH etching to the u-GaN epilayer after the removal of sapphire was conducted and effect of KOH etching time on the device performance of the fabricated Schottky diodes was also investigated. Vertical-structured GaN SBDs with die size of 400×400 µm2 and Schottky contact area of 200 µm in diameter have been successfully fabricated. The extracted values of Schottky barrier height (ΦB), series resistance (Rs), and ideality factor (η) of the 60-s-KOH etched SBDs were 0.78 eV, 1.9 mΩ, and 1.06, respectively.

Vertical-structured Ni/n-GaN schottky diode with electroplating nickel substrate

For the past decade, most of vertical device applications of GaN were processed by either wafer bonding or direct epitaxy on SiC or GaN wafer. However, the former usually suffers from large strain between GaN and bonding wafer because the high temperature and high pressure bonding process, and the later is not cost effective because of using SiC or GaN substrate. In this work, a novel vertical structure of Ni/n-GaN Schottky barrier diode (SBD) with metallic substrate employing nickel electroplating and laser lift-off (LLO) processes is proposed and its electrical characteristics is reported

Hydrogen and oxygen plasma effects on undoped and n-p compensation-doped single- and multilayer polycrystalline silicon resistor films

In this study, we investigate hydrogen and oxygen plasma effects on undoped and n–p compensation-doped polycrystalline silicon (poly-Si) resistors. The current–voltage (I–V) characteristics, channel resistance (Rp), contact region resistance (Rj), total resistance (RT=Rp+Rj), and activation energy of the poly-Si resistors with different film lengths and passivation layers were measured and analyzed. It is found that the film resistance has been strongly enhanced by either hydrogen or oxygen plasma treatments, which is attributed to the neutralization effect of plasma treatment inside the grain being overridden by the passivation effect at the grain boundary. Moreover, it is seen that both the total resistance and activation energy of undoped intrinsic films are larger than those of n–p compensation-doped films. To realize a high-value poly-Si resistor, a novel multilayer structure is proposed for the first time. Compared with the conventional single-layer structure, it is seen that the relatively smaller grain size in a four-layer structure results in an approximately 25–50% increase in resistance.