Kea-Joon Yang

Growth and properties of the Cd1−xZnxS thin films for solar cell applications

Cd1−xZnxS (0≤x≤1) thin films have been prepared by the co-evaporation of CdS and ZnS. When the ZnS mole ratio was less than 0.85, the crystal structure of Cd1−xZnxS films was hexagonal with the c axis aligned perpendicular to the substrate. For x>0.85, however, the Cd1−xZnxS films were grown with cubic zincblende structure. As the ZnS mole ratio increased, the lattice constant of Cd1−xZnxS films decreased. The optical band gap of Cd1−xZnxS films varies from 2.41 eV for CdS to 3.48 eV for ZnS with x. The open circuit voltage of Cd1−xZnxS/CdTe solar cells increased with x due to reducing of the electron affinity difference between Cd1−xZnxS and CdTe films, having approximately 830 mV of the maximum value at x=0.35.

Leakage current monitoring and outdoor degradation of silicone rubber

The degradation process of silicone rubber was investigated by leakage current monitoring in the inclined-plane method. A data acquisition system (DAS) with 12-bit, 8-channel analog/ digital (AD) converter was prepared. The maximum erosion depth was measured for use as the degradation indicator. The result suggests that the discharge duration and current waveform are well corresponding with the degradation process. And fast Fourier transform (FFT) analysis from the stored waveform shows that the harmonic ratio I3/I1 corresponds with the initial surface transition from hydrophobic to hydrophilic, and with further progressive degradation. In addition, it may be possible to use cumulative charge and peak pulses as quantitative indicators of failure. Furthermore, the contact angle was adopted for assessing surface degradation. These results indicate that the surfaces are divided into top and bottom areas depending on the degree of exposure to dry band arcing. It seems that the bottom area subjected to most of the dry band arcing contains very short chains of silicone rubber as well as alumina trihydrate fillers, while the top area shows the loss of filler particles.

Characteristics of the CdZnS thin film doped by indium diffusion

Abstract Effects of the thickness of indium films and the annealing temperature on structural, optical and electrical properties of chemically deposited CdZnS films were investigated. The diffusion process of evaporated indium was carried out by heating the sample in air at 150–550 °C for 1 h. X-Ray diffraction patterns of CdZnS films indicate that the minimum thickness and annealing temperature for the formation of an In 2 O 3 layer, which acts as a barrier preventing the out-diffusion of indium and gives a high optical transmittance, are 20 nm and 350 °C, respectively. As the thickness of indium film and the annealing temperature increase, the conductivity of CdZnS films improves and the lowest resistivity of 0.3 Ω-cm is attained for CdZnS films with a 40 nm indium coating and annealed at 450 °C.

Effects of the Growth Temperature on the Properties of CdTe Thin Films for Solar Cell Applications

CdTe films for solar cell application were prepared at various growth temperatures by a vacuum evaporation system having close spacing between the source and substrate. The CdTe thin films had a cubic structure highly oriented with the (111) direction perpendicular to the substrate surface, regardless of the growth temperature. The crystallites are of random shape and reach up to about 2 µm in size with increasing growth temperature. The higher growth temperature contributed to the reduction of dark resistivity from 6 ×107 Ωcm at room temperature to 45.4 ×106 Ωcm at 300°C. The photovoltaic properties of the CdS/CdTe solar cell were considerably improved with the increase in the growth temperature, which was caused by the increase of (111) texture and grain size in CdTe films.

Improvement of Etch Rate and Profile by SF 6 , C 4 F 8 , O 2 Gas Modulation

Deep trench etching of silicon was investigated as a function of RF source power, DC bias voltage, gas flow rate, and gas addition. On increasing the RF source power from 300 W to 700 W, the etch rate was increased from to . The addition of gas improved the etch rate and the selectivity. The highest etch rate is achieved at the gas addition of 12 %, The selectivity to PR was 65.75 with gas addition of 24 %. At DC bias voltage of -40 V and gas flow rate of 30 seem, We were able to achieve etch rate as high as with good etch profile.

Influence of Sputter Power on the Structural and Optical Properties of CdS Films for Photovoltaic Applications

CdS films have been prepared on polycarbonate, polyethylene terephthalate, and Coming 7059 substrates by r.f magnetron sputtering technique at room temperature. A comparison of the properties of the films deposited on polymer and glass substrates was performed. In addition, the influence of the sputter power on the structural and optical properties of these films was evaluated. The XRD measurements revealed that CdS films were polycrystalline and retained the mixed structure of hexagonal wurtzite and cubic phase, regardless of substrate types. As the sputter power was increased from 75 to 150 Watt, the structure of CdS films was converted from the mixed of hexagonal and cubic phase to hexagonal phase. The morphology of CdS films is found to be continuous and dense. Also, the grain of CdS films is larger with increasing the sputter power. The average transmittance exceeded 80 % in the visible spectrum for all films and decreases slightly with the sputter power.

A Study on Properties of ZnO:Al Films on PC Substrate for Solar Cell Applications

Al doped ZnO thin films (ZnO:Al) were deposited on poly carbonate (PC) substrate by rf magnetron sputtering. In addition, the electrical, optical properties of the films prepared at various conditions were investigated. As the sputter power increased, the resistivity of ZnO:Al films decreased, regardless of substrate types. However, the resistivity of the films increased with the sputter pressure. The ZnO:Al films were increasingly dark gray colored as the sputter power increased, resulting in the loss of transmittance. High quality films with resistivity as low as 1.4310 Ω-cm and transmittance over 80 % have been obtained by suitably controlling the deposition parameters.

N2 Plasma Treatment Effects of SiNx Buffer Layer for Low Temperature Process

To adopt thin film transistor (TFT) type FRAM, low temperature process is necessary. SiNx has good properties and advantages as a low temperature processed buffer layer. The SiNx films were grown on the p-Si(100) substrate by the transformer coupled plasma chemical vapor deposition (TCP-CVD). By employing N2 plasma treatment, interface traps such as mobile charges and injected charges were removed, hysteresis of capacitance-voltage (C-V) curve disappeared. After N2 plasma treatment, a leakage current was decreased about 2 orders. The memory window of low temperature processed (at 550°C) metal-ferroelectric-insulator-silicon (MFIS) capacitor was as large as about 1.5 V.

Improvement of Dielectric and Interface Properties of CeO2 Buffer Layer by Using the Metal Seed Layer and N2 Plasma Treatment

In this paper, we investigated the feasibility of cerium oxide (CeO2) films as buffers layer of MFIS (metal ferroelectric insulator semiconductor) type capacitors. CeO2 layer were prepared by a two-step process of a low temperature film growth and subsequent RTA (rapid thermal annealing) treatment. By applying a cerium (Ce) metal seed layer of 4 nm, unwanted SiO2 layer generation was successfully suppressed at the interface between the buffer layer and the Si substrate. After N2 plasma treatment, the leakage current was reduced by about 2-orders. By employing a N2 plasma treatment, we were able to successfully obtain good properties at the interface between the buffer layer and the Si substrate.

Structural and Electrical Properties of Co-evaporated Cu(In 1-x ,Ga x )Se 2 Thin Film Solar Cells with Varied Ga Content

thin films have been considered as an effective absorber material for high efficient solar cells. In this paper, the CIGS thin films with varied Ga content were prepared using a co-evaporation process of three stage. We carry out structure and electrical optical property on the thin film in varied Ga content. CIGS thin films have been characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy-dispersive spectroscopy(EDS), four-point probe measurement, and the Hall measurement. To optimize Ga contents, Ga/(In+Ga) ratio were changed from 0.13 to 0.72. At this time the carrier concentrations were varied from to , and electrical resistivity were varied from to . A strong orientation and a lager grain size were obtained at a Ga/(In+Ga) of 0.3. We were able to achieve conversion efficiency as high as 15.95% with a Ga/(In+Ga) of 0.3.