Li-Ren Lou

Mechanisms of high quality i-ZnO thin films deposition at low temperature by vapor cooling condensation technique

A comparative mechanism investigation on the structural and optoelectronic properties of i-ZnO thin films, deposited on the silicon substrates at various temperatures were conducted. The experimental results verified that the i-ZnO films deposited at a low temperature have better quality over the conventional high temperature deposited ones. This low temperature deposition by using vapor cooling condensation technique has been successfully used to fabricate optoelectronic devices, such as UV light-emitting diodes and UV photodetectors. The mechanisms responsible for the fact that the low temperature deposited samples had better quality were analyzed in terms of the adsorption/desorption and diffusion of ZnO particles in the growth process.A comparative mechanism investigation on the structural and optoelectronic properties of i-ZnO thin films, deposited on the silicon substrates at various temperatures were conducted. The experimental results verified that the i-ZnO films deposited at a low temperature have better quality over the conventional high temperature deposited ones. This low temperature deposition by using vapor cooling condensation technique has been successfully used to fabricate optoelectronic devices, such as UV light-emitting diodes and UV photodetectors. The mechanisms responsible for the fact that the low temperature deposited samples had better quality were analyzed in terms of the adsorption/desorption and diffusion of ZnO particles in the growth process.

Performance Improvement of ( NH4 ) 2S x -Treated III–V Compounds Multijunction Solar Cell Using Surface Treatment

To improve the conversion efficiency of tandem-type III-V multijunction solar cells, the (NH 4 ) 2 S x -treatment method was used to passivate the surface of the window layer (AlInP) of the cell. The conversion efficiency of the (NH 4 ) 2 S x -treated multijunction solar cell was increased more than 4%. Using X-ray photoelectron spectroscopy and current-voltage measurements, the mechanism of the conversion efficiency improvement is attributed to the reduction of the surface states by sulfidation passivation. It is indicated that the (NH 4 ) 2 S x treatment is an effective method for improving the performance of III-V compound multijunction solar cells.

Investigation of Förster-type energy transfer in organic light-emitting devices with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethy ljulolidin-4-yl-vinyl)-4H-pyran doped cohost emitting layer

Organic light-emitting devices (OLEDs) with cohosted emitter, which is composed of 9,10-di(2-naphthyl)anthracene (ADN) and tris(8-hydroxy-quinolinato) aluminum (Alq3) and doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethy ljulolidin-4-yl-vinyl)-4H-pyran (DCJTB), were fabricated and studied. The efficiency of OLEDs with a cohost emitter was higher than that with a single host emitter. For the cohost emitter with ADN/Alq3 weight ratio of 75:25, the 3.4 cd/A efficiency of the resulted OLEDs was obtained. It is found that the absorption spectra of DCJTB and the emission spectra of Alq3 changed with the composition of the emitter. This phenomenon is attributed to the polarization effect. On the basis of the Forster’s theory, the resulted overlap integral exhibits the highest value for this cohost emitter. The experimental results reveal that the cascade energy transfer plays an important role in the luminance efficiency enhancement of the cohost emitter in OLEDs.

Mechanism Investigation of p-i-n ZnO-Based Light-Emitting Diodes

Using a cosputtering technique to deposit P-ZnO : AlN film and using a vapor cooling condensation system to deposit n-ZnO : In and i-ZnO films on sapphire substrates, thin-film-type ZnO-based light-emitting diodes (LEDs) were fabricated. A Nd : YAG laser with a wavelength of 413 nm is utilized to identify the defect-related emissions of p-ZnO, i-ZnO, and n-ZnO films. The characteristics of i-ZnO layer of ultraviolet (UV) emissions were analyzed using temperature-dependent photoluminescence. The mechanism of the UV electroluminescence emission peak at 3.20 eV observed from the p-i-n ZnO-based LEDs were attributed to the low deep-level defects and the radiative recombination occurred in the i-ZnO layer.

Structure and photoluminescence of Ge nanoclusters embedded in GeOx films deposited using laser assistance at low temperature

Crystalline Ge nanocluster-embedded GeOx films were deposited at low temperature using a laser-assisted plasma enhanced chemical-vapor deposition system. The structural and optical properties of the films deposited under various power densities of the assisting CO2 laser beam were investigated. The size of the Ge nanoclusters decreased and the number density of the Ge nanoclusters increased with an increase in the laser power used in the film deposition. The Ge nanoclusters crystallization was improved with an increase in the assisting laser power. The observed photoluminescence (PL) characteristics, including the spectral position, decay curve, and intensity of the emission bands, can be attributed to the quantum confinement effect. These experimental results verified that the PL emission originated from the recombination of electron-hole pairs in the Ge nanoclusters. Furthermore, the growth process of the Ge nanoclusters was qualitatively studied.

Influence of Deposition Conditions on Silicon Nanoclusters in Silicon Nitride Films Grown by Laser-Assisted CVD Method

Crystalline-silicon-nanocluster-embedded silicon nitride films were deposited at low temperature using a laser-assisted CVD (LACVD) system with various reactant gas flow rates and assisting laser power densities. The photoluminescence (PL) performances of the resultant films were studied, showing a systematic spectra blue shift, and the enhancement of PL intensity with the increase of the reactant NH3/SiH4 gas flow rate ratio and the assisting laser power density used in the film deposition. The spectra blue shift can be ascribed to the decrease of the size of the nanoclusters in the films. It is also deduced that both the reduction of the amount of nonradiative centers in the nanoclusters and the increase of the number density of the nanoclusters in the film are responsible for the enhancement of the PL intensity. The film growth process is also briefly discussed.

GaAs MOS Diodes with the Gate Oxide Formed by PEC Method

Department of Electro-Optical Engineering, National Cheng Kung University, Tainan 701, Taiwan, R. O. C Phone: +886-6-2757575-62393 Fax: +886-6-2362303 E-mail: hylee@ee.ncku.edu.tw Institute of Electro-Optical and Materials Science, National Formosa University, Yunlin 653, Taiwan, R. O. C Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan, R.O.C

ZnO Nanorods-on-GaN Heterojunction Light-Emitting Diode Grown by Vapor Cooling Condensation Method

1.Introduction Zinc oxide (ZnO) is a promissing material for fabricating short-wavelength light-emitting devices, such as LEDs[1] and laser diodes (LDs)[2] due to its wide band gap (~3.37 eV) and high exciton binding energy (~60 meV). Various methods such as chemical vapor deposition, sputter, molecular beam epitaxy and vapor cooling condensation method have been used to deposit ZnO films[3-6]. Recently, because of great interests on the quantum confinement effect and nano-devices, one-diemensional ZnO nanorod-structure has been investigated widely[7,8]. In this study, a vapor cooling condensation method was used to grow ZnO nanorods on p-GaN at low temperature using anodic alumina membrane (AAM) template. The deposited ZnO nanorods were then used to construct two types of nano-heterojunction LEDs. And their electroluminescence was demonstrated and discussed.