Chih-Chien Lin

Current spreading of III-nitride light-emitting diodes using plasma treatment

In this study, (CF4+O2) plasma is used to selectively treat the p-type GaN region underneath the bonding pad of the anode electrode of III-nitride light-emitting diodes (LEDs). A more uniform light emission distribution is observed in the far-field pattern of the plasma-treated devices and a 16% enhancement of the output intensity under the same biasing current is obtained. The maximum current that can be applied is also higher for the plasma-treated device. Not only does the plasma treatment of the p-GaN layer lead to a highly insulating region but also it does not degrade the device performance. Results from this study indicate that the plasma treatment is able to improve the current spreading of the III-nitride LEDs.

Changes in surface state density due to chlorine treatment in GaN Schottky ultraviolet photodetectors

A chlorination surface treatment was used to reduce the surface density of states of a n-type GaN surface, which improves the Schottky performances of the resultant metal-semiconductor contact. Using capacitance-frequency measurement, the surface state density of the chlorine-treated GaN surface was about one order less than that without chlorination treatment. The dark current of the chlorine-treated GaN ultraviolet photodetectors (UV-PDs) is 1.5 orders of magnitude lower than that of those without chlorination treatment. The products of quantum efficiency and internal gain of the GaN Schottky UV-PDs without and with chlorination treatment under conditions of −10 V reverse bias voltage at a wavelength of 330 nm were 650% and 100%, respectively. The internal gain in chlorine-treated GaN UV-PDs can therefore be reduced due to a decrease in the surface state density.

GaN-Based Resonant-Cavity Light-Emitting Diodes With Top and Bottom Dielectric Distributed Bragg Reflectors

Dielectric distributed Bragg reflectors (DDBRs) were employed as the top and bottom mirrors to form a Fabry-Pérot resonator of GaN-based resonant-cavity light-emitting diodes. The DDBR consisting of TiO2 and SiO2 dielectric pairs was deposited using an electron-beam deposition system with optical monitoring system to obtain high reflection precisely at blue light wavelength. The pairs of top and bottom reflectors were 9 and 10 that represent high reflection of 93.2% and 95% at a blue wavelength of 448 nm, respectively. An increase of 245% of light output intensity and a decrease of 10 nm of the full-width at half-maximum of the light output intensity were attributed to the resonance effect caused by the top and bottom DDBRs.

Light Output Enhancement of GaN-Based Light-Emitting Diodes Using ZnO Nanorod Arrays Produced by Aqueous Solution Growth Technique

ZnO nanorod arrays were successfully deposited on GaN-based light-emitting diodes (LEDs) using the aqueous solution growth technique. A 20.3% light output enhancement of the LEDs with ZnO nanorod array was obtained at an injection current of 100 mA. With the presence of the ZnO nanorod array, divergence of the light output was reduced and the light output was confined in a smaller escape cone of about 30° rather than 42° of the conventional LEDs. Current-voltage characteristics and electroluminescence measurements confirmed that there was no significant change in electrical and optical properties of these LEDs with ZnO nanorod arrays.

Enhanced Light Extraction Mechanism of GaN-Based Light-Emitting Diodes Using Top Surface and Side-Wall Nanorod Arrays

Using a self-catalyst vapor-liquid-solid mechanism, random indium-tin-oxide (ITO) nanorod arrays were deposited on the top surface and side-wall of GaN-based light-emitting diodes (LEDs) by electron-beam deposition. When the side-wall nanorod arrays and the top surface ITO nanorod arrays were deposited at an oblique-angle of 45°, roughened surface morphology and matched refractive index of 1.6 between air and the p-GaN layer could be obtained. Comparing the conventional LEDs without ITO nanorod arrays, a 34% light output power increase was attributed to the roughened top and side-wall surface morphology and the matched refractive index caused by the ITO nanorod arrays. Not only were the side-wall nanorod arrays used to increase light output power, but the light output divergence angle could be widened by using side-wall nanorod arrays.

Enhanced Light Extraction of GaN-Based Light Emitting Diodes Using Nanorod Arrays

Using a self-shadowing nature, various indium tin oxide (ITO) nanorod arrays were deposited on the surface of GaN-based light emitting diodes (LEDs) by an electron-beam deposition system. The surface morphology and effective refractive index could be controlled by the oblique angle of the deposited ITO nanorod arrays. The surface morphology and the matching refractive index of 1.6 between air and p-GaN layer were obtained for the ITO nanorod arrays with an oblique angle of 45°. Comparing the conventional LEDs without ITO nanorod arrays, the light output power increase of 26.4% is attributed to the surface morphology and the matching refractive index obtained by the ITO nanorod arrays.

Work Function Tailoring of Carbon-Added Tungsten Gate Electrodes

In this work, carbon-added tungsten (W 1-x C x , x ≤ 0.19) and thin carbon layer-inserted tungsten (W top /C/W bottom , the thickness of W bottom is set to be 2 nm and 10 nm) gate stacks are deposited on SiO 2 /Si to fabricate metal-oxide-semiconductor capacitors. Grazing incident angle X-ray diffraction reveals that the W 1-x C x films become amorphous when the concentration of added C is lower than 16 atom %. However, when the C concentration is as high as 19 atom %, a trace of γ phase of tungsten carbide phase appears in the W 0.81 C 0.19 film. No interdiffusion between C-added W and SiO 2 is observed by Auger electron spectroscopy depth profiling. The resistivity of W, W 0.88 C 0.12 , W 0.84 C 0.16 , and W 0.81 C 0.19 are 132, 151, 163, and 337 μΩ cm, respectively. The work function of W 0.81 C 0.19 , W 0.84 C 0.16 , W 0.88 C 0.12 , W, W/C/W (10 nm), and W/C/W (2 nm) on SiO 2 are 4.82, 4.75, 4.73, 4.66, 4.52, and 4.32 eV, respectively. The C-related dipole shows apparent influence on the work function. The leakage current densities of C-added W films are smaller than 2 × 10- 5 A/cm 2 in the range from 0 to 5 × 10 7 V/cm. No significant influence of these gate electrodes on the fixed oxide charge and the leakage behavior of SiO 2 are observed.

The Influence of Si Content on the Work Function of W1 − x Si x ( x ≤ 14 atom % ) Gate Electrodes

W 1-x Si x (W 0.90 Si 0.10 and W 0.86 Si 0.14 ) films are deposited on SiO 2 /Si substrates by cosputtering from W and Si targets to form metal-oxide-semiconductor capacitors. After deposition, the samples are subjected to a thermal anneal at 700°C in flowing N 2 ambient. Only body-centered-cubic W and/or β-W are present in the W 1-x Si x films and no tungsten silicide can be found. However, the lattice constant of W is changed by adding Si and annealing treatment. Work functions of as-deposited W 0.90 Si 0.10 and W 0.86 Si 0.14 are 4.57 and 4.47 eV, respectively. After annealing at 700°C, the work functions of W 0.90 Si 0.10 and W 0.86 Si 0.14 become 4.52 and 4.38 eV, respectively. The connection between the work function and material characteristics of W 1-x Si x is discussed

Mechanisms and high performances of chlorine-treated GaN ultraviolet photodetectors

A chlorination surface treatment was used to reduce the surface states of an n-type GaN surface, which improves the Schottky performances of the resultant metal-semiconductor contact. At a reverse bias of 10V, the dark current of the GaN-based UV-PDs with and without chlorinated surface treated were 28.1nA and 0.59μA, respectively. The dark current of chlorine-treated Schottky UV-PDs was 21 times of magnitude smaller than that of those without chlorination treatment. The product of quantum efficiency and internal gain of the GaN Schottky UV-PDs without and with chlorination treatment under a reverse voltage of 10V at a wavelength of 330nm was 650% and 100%, respectively. The internal gain of chlorine-treated GaN UV-PDs can be reduced due to the improvement of surface state density.

Enhanced vertical emission from GaN based light emitting diode with ZnO nanorod arrays produced by hydrothermal method

In this study, we analyzed the modulated light output from the GaN based light emitting diodes (LEDs) with the incorporation of ZnO nanorod by hydrothermal method. With the ZnO nanorod, the light output from the LEDs increased by 20.2% and more interestingly, output power was more concentrated in a smaller escape cone of~ �� =30 o than that of conventional LEDs with a cone of~�� =42 o . Surface damaging of LEDs was also avoided by the low temperature hydrothermal growth of ZnO nanorod arrays. Experiments and Discussion- The epitaxial layers of the InGaN/GaN multiple quantum well (MQW) LEDs were grown on c-plane sapphire substrate by MOCVD technique. The structure is composed of a 50-nm-thick GaN buffer layer, a 3-µm-thick Si-doped GaN layer (3×10 17 cm -3 ), an undoped InGaN/GaN multiple quantum