Hong Seong Kang

Annealing effect on the property of ultraviolet and green emissions of ZnO thin films

The mechanism of ultraviolet (UV) and green emission of ZnOthin filmsdeposited on (001) sapphire substrates by pulsed laser deposition was investigated by using postannealing treatment at various annealing temperatures after deposition.Structural, electrical, and optical properties of ZnOfilms have been also observed. As the postannealing temperature increased, the intensity of UV (380 nm) peak and the carrier concentration were decreased while the intensity of the visible (about 490–530 nm) peak and the resistivity were increased. The role of oxygen in ZnOthin film during the annealing process was important to the change of optical properties. The mechanism of the luminescence suggested that UVluminescence of ZnOthin film was related to the transition from near band edge to valence band, and green luminescence of ZnOthin film was caused by the transition from deep donor level to valence band due to oxygen vacancies. The activation energy derived by using the variation of green emission intensity was 1.19 eV.

Structural, electrical, and optical properties of p-type ZnO thin films with Ag dopant

p-type ZnO films have been fabricated on a (0001) Al2O3 substrate, using Ag2O as a silver dopant by pulsed laser deposition. The structural property of those films is systematically characterized by observing the shift of (0002) peak to investigate the substitution of Ag+ for Zn+. Narrow deposition temperature for Ag-doped p-type ZnO films has been obtained in the range of 200–250°C with the hole concentration of 4.9×1016–6.0×1017cm−3. A neutral acceptor bound exciton has been clearly observed by photoluminescence emitted at 3.317eV in Ag-doped p-type ZnO thin films.

Investigation on the p-type formation mechanism of arsenic doped p-type ZnO thin film

The photoluminescence spectra of As doped p-type ZnO thin films reveal neutral acceptor bound exciton of 3.3437eV and a transition between free electrons and acceptor levels of 3.2924eV. Calculated acceptor binding energy is about 0.1455eV. Thermal activation and doping mechanism of this film have been suggested by the analysis of x-ray photoelectron spectroscopy. p-type formation mechanism of As doped ZnO thin film is related to the AsZn–2VZn complex model. ZnO-based p-n junction was fabricated by the deposition of an undoped n-type ZnO layer on an As doped p-type ZnO layer.

Synthesis and analysis of Ag-doped ZnO

The solid-solid interaction and thermal decomposition behavior of 2wt% Ag2O in ZnO powder have been investigated by using thermogravimetry analysis and differential thermal analysis. Ag2O, which remained stable in ZnO up to 200°C, was observed to be thermally decomposed to Ag+ ions in the temperature range of 200–250°C, suggesting that Ag+ ions were diffused into ZnO matrix. Based on thermal analysis, ZnO:Ag films have been fabricated on a (001) Al2O3 substrate using specifically synthesized Ag-doped ZnO target by pulsed laser deposition. The effect of (002) peak shift on the structural property of Ag-doped ZnO films has been systematically characterized to investigate the influence of the substitution of Ag+ for Zn+. Ag-doped p-type ZnO films have been successfully grown at a deposition temperature in the range of 200–250°C, which is in good agreement with thermally decomposed temperature for Ag2O to Ag+ in ZnO powder, with hole concentrations of 4.9×1016–6.0×1017cm−3, hole mobilities of 0.29–2.32cm2∕Vs,...

Effect of rapid thermal annealing on electrical and optical properties of Ga doped ZnO thin films prepared at room temperature

Ga doped ZnO (GZO) thin films were prepared by pulsed laser deposition on glass substrate at room temperature. Structural, optical, and electrical properties of these films were analyzed in order to investigate their dependence on oxygen pressure and rapid thermal annealing (RTA) temperature. High quality GZO films with a low resistivity of 2.92×10−4Ωcm and a transparency above 94% were able to be formed at an oxygen pressure of 3×10−2Torr and a RTA temperature of 400°C. A four point probe method, x-ray diffraction, atomic force microscopy, and ultraviolet–near-infrared grating spectrometer are used to investigate the properties of GZO films.

Annealing effect on the structural and optical properties of ZnO thin film on InP

Abstract II–VI semiconducting ZnO thin films have been fabricated by pulsed laser deposition (PLD) process on indium phosphide (InP) (100) substrates. Thin films were annealed at various temperatures in order to study the annealing temperature dependence of the structural and optical properties of ZnO thin film grown on InP substrate. The structural and optical properties were characterized with X-ray diffraction (XRD) and photoluminescence (PL), respectively. In our study, we have found some defect levels from the PL spectra and derived the defect centers activation energy. According to XRD data, it could be thought that the films had some strains but relaxed by annealing processes.

Optical property and Stokes’ shift of Zn1−xCdxO thin films depending on Cd content

Ternary Zn1−xCdxO films were grown on (0001) sapphire substrates by pulsed laser deposition. The energy band gap of Zn1−xCdxO films decreases with increasing Cd content. An increase of Cd content also leads to the emission broadening, absorption edge broadening, and crystallinity degradation. The absorption edge and ultraviolet emission energy shift to lower energy from 3.357eVto3.295eV and 3.338eVto3.157eV, respectively, with increasing Cd content from 0.3% to 3% at 4K. The Stokes’ shift between the absorption and emission is observed and that indicates the increase of exciton localization with Cd content.

Effect of Si Layer in The ZnO Thin Films by Pulsed Laser Deposition

ZnO thin films and ZnO-Si-ZnO multi-layer thin films have been deposited by pulsed laser deposition (PLD). And then, the films have been annealed at 300°C in oxygen ambient pressure. The optical and structural properties changed by Si layer in ZnO thin film. UV and visible peak position was shifted by Si layer. Electrical properties of the films were improved slightly than ZnO thin film without Si layer. The optical and structural properties of ZnO thin films and ZnOSi-ZnO multi-layer thin films were characterized by PL (Photoluminescence) and XRD(X-ray diffraction method), respectively. Electrical properties were measured by van der Pauw Hall measurements.

Effect of Cu Dopant on the Electrical Property of ZnO Thin Films Deposited by Pulsed Laser Deposition

Cu-doped ZnO (denoted by ZnO:Cu) films have been prepared by pulsed laser deposition using 3 wt. CuO doped ZnO ceramic target. The carrier concentrations (1011~1018 cm-3) and, electrical resistivity (10-1~105 cm) of deposited Cu-doped ZnO thin films were varied depending on deposition conditions. Variations of electrical properties of Cu-doped ZnO indicate that copper dopants may play an important role in determining their electrical properties, compared with undoped films. To investigate effects of copper dopants on the properties of ZnO thin films, X-Ray diffraction (XRD), photoluminescence (PL), and Hall measurements have been performed and corresponded.

Neural network based modeling for the growth rate of ZnO thin films on the pulsed laser deposition

In this study the D-optimal design was used to make design matrix in this experiment. Neural networks (NNets) based on the backpropagation (BP) algorithm are applied to the pulsed laser deposition (PLD) process modeling in order to construct the model for the growth rate of the ZnO thin films.