[Show abstract][Hide abstract] ABSTRACT: Nitride-based light emitting diodes (LEDs) with sidewall texture and pillar waveguides (STPW) were fabricated using conventional lithography method. With 20-mA injection current, it was found that forward voltages were 3.16 and 3.15 V for the conventional LED and the LED with STPW, respectively. It was also found that 20-mA LED output powers were 8.4 and 10.1 mW for conventional LED and the LED with STPW, respectively. The enhancement is attributed to the out-coupling of lateral waveguide mode in the near horizontal directions
[Show abstract][Hide abstract] ABSTRACT: We present the characteristics of novel GaN-based ultraviolet (UV) Schottky barrier photodetectors (PDs) with a low-temperature (LT-)AlN cap layer. Comparing them with conventional Schottky barrier PDs, it was found that we achieved smaller dark current and larger UV to visible rejection ratio from the PDs with the LT-AlN cap layer. The dark leakage current for the Schottky barrier PDs with the LT-AlN cap layer was shown to be about four orders of magnitude smaller than that for the conventional Schottky barrier PDs. With −5 V applied bias, the measured responsivity and UV to visible rejection ratio are 0.16 A /W and 7.74×102 for the Schottky barrier PDs with the LT-AlN cap layer, respectively. This result can be attributed to the thicker and higher potential barrier when the LT-AlN cap layer was inserted.
Superlattices and Microstructures 01/2006; 40(4):470-475. · 1.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitride-based flip-chip indium-tin-oxide (ITO) light-emitting diodes (LEDs) were successfully fabricated. It was found that the forward voltage and the 20 mA output power of the flip-chip ITO LED were 3.32 V and 14.5 mW, respectively. Although the operation voltage of such a flip-chip ITO LED was slightly larger, it was found that its output power was much larger than those of conventional nonflip-chip LEDs. It was also found that flip-chip ITO LEDs were more reliable.
IEEE Transactions on Advanced Packaging 06/2005; · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The undoped GaN (u-GaN) and two-dimensional electron gas (2DEG) metal–semiconductor–metal (MSM) photodetectors with semi-transparent Ni/Au Schottky barrier contact electrodes were fabricated. It was found that we could achieve a larger Ni/Au transmittance, higher Schottky barrier heights and larger photocurrent to dark current contrast ratios by photo-chemical annealing of these photodetectors in O2. It was also found that the maximum quantum efficiencies were 13% and 57% for the photo-chemical annealing u-GaN and 2DEG photodetectors, respectively. Furthermore, it was found that we could achieve a larger responsivity, a lower noise level and a larger detectivity by using the 2DEG structure.
[Show abstract][Hide abstract] ABSTRACT: Resonant cavity light emitting diodes (RCLEDs) containing nine sheets of self-organized InAs quantum dot (QD) active layers and operating at around 1.3μm are demonstrated. The structure was grown directly on GaAs substrates, which includes selectively oxidized AlOx current apertures and intracavity metal contacts. It was found that the average operating resistance is 60Ω, while the average turn-on voltages is 1.6V. It was also found that temperature coefficient of these RCLEDs was about 0.11nm/°C.
Materials Science and Engineering B 07/2004; 110(3):256-259. · 1.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitride-based light-emitting diodes (LEDs) with textured side walls were fabricated. By using plasma-enhanced chemical vapor deposition SiO<sub>2</sub> layer as the etching mask, we successfully etched the nitride epitaxial layers to achieve wavelike side walls. It was found that such wavelike side walls could mainly enhance the light output at the horizontal directions. With a 20-mA current injection, it was found that the output powers of the LED with textured side walls and normal LED were 9.3 and 8.4 mW, respectively. Furthermore, it was found that such textured side walls will not result in a higher operation voltage.
[Show abstract][Hide abstract] ABSTRACT: GaN epitaxial layers and InGaN/GaN multiquantum well blue light emitting diodes (LEDs) were prepared on both patterned sapphire substrates (PSS) and conventional sapphire substrates. From scanning electron microscopy micrographs of GaN epitaxial layers on PSS, it was found that lateral growth indeed occurred and the lateral to vertical growth rate ratio was around 2. It was also found that we could enhance the LED output power by using lateral epitaxial patterned sapphire. Such an enhancement could be attributed to the reduced dislocation density in the lateral growth regions of the epitaxial layers.
[Show abstract][Hide abstract] ABSTRACT: GaN-based light-emitting diodes (LEDs) with various p-cap layers were prepared. It was found that surface morphologies of the LEDs with 800°C grown cap layers were rough due to the low lateral growth rate of GaN. It was also found that 20-mA forward voltage of the LED with 800°C grown p-AlInGaN-GaN double-cap layer was only 3.05 V. Furthermore, it was found that we could achieve a high output power and a long lifetime by using the 800°C grown p-AlInGaN-GaN double-cap layer.
[Show abstract][Hide abstract] ABSTRACT: Modulation doped Al<sub>0.12</sub>Ga<sub>0.88</sub>N-GaN superlattice structures were used to spread pulse current in nitride-based light emitting diodes (LEDs). Although the 20-mA electroluminescence (EL) intensity of the LEDs with modulation-doped AlGaN-GaN superlattice structures was found to be 10% smaller than that of the conventional LEDs, it was found that LEDs with the AlGaN-GaN superlattice structures could all endure a 2000-V reverse electrostatic discharge (ESD) pulse voltage. Some LEDs can even survive with an 8000-V reverse ESD pulse voltage, which is equivalent to "Class 3B" of Human Body Mode testing.
IEEE Transactions on Electron Devices 01/2004; 51(10):1743-1746. · 2.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: GaN n+–p junction diodes were fabricated by implanting Si atoms into p-GaN. It was shown that we could use these diodes as GaN-based planar photodetectors. It was found that the dark current density of the diodes was around 1.5 μA/cm2 and 50 nA/cm2 at reverse biases of 3 and 1 V, respectively. Spectra response measurements revealed a cutoff wavelength at around 365 nm and a peak responsivity of 0.33 mA/W at 365 nm for the GaN planar n+–p photodetectors. It was also found that the visible rejection ratio was around 260. Furthermore, temporal response measurements revealed that the fall times of these GaN planar n+–p photodetectors were found to be shorter than 0.4 μs.