Dong-Gun Lim

High-density inductively coupled plasma chemical vapor deposition of silicon nitride for solar cell application

Abstract The silicon nitride films were deposited by means of high-density inductively coupled plasma chemical vapor deposition in a planar coil reactor. The process gases used were pure nitrogen and a mixture of silane and helium. Passivated by silicon nitride, solar cells show efficiency above 13%. Strong H-atom release from the growing SiN film and Si–N bond healing are responsible for the improved electrical and passivation properties of SiN film. This paper presents the optimal refractive index of SiN for single layer antireflection coating as well as double layer antireflection coating in solar cell applications.

The effects of a double layer anti-reflection coating for a buried contact solar cell application

Abstract Theoretical and experimental investigations were performed on a double layer anti-reflection (DLAR) coating of MgF 2 /CeO 2 . We investigated CeO 2 films as an AR layer because they have a proper refractive index of 2.46 and demonstrate the same lattice constant as the Si substrate. An optimized DLAR coating showed a reflectance value as low as 1.87% over wavelengths ranging from 0.4 to 1.1 μm. Buried contact solar cells (BCSC) were investigated using the following structure: MgF 2 /CeO 2 /Ag/Cu/Ni grid/n + emitter/p-type Si base/P + /Al. The BCSC efficiency under an illumination of 50 mW/cm 2 measured as high as 19.9% when employing DLAR coatings. MgF 2 /CeO 2 DLAR coatings on the BCSC cell contributed to an increase of the fill factor (from 71% to 75%) and the J sc (from 19.8 mA/cm 2 to 22.6 mA/cm 2 ).

Characteristics of LiNbO3 memory capacitors fabricated using a low thermal budget process

Abstract We investigated LiNbO3 metal ferroelectric semiconductor (MFS) capacitors because of the following advantages: a low interface trap density, a low interaction with Si substrate, and a large remanent polarization. Ferroelectric LiNbO3 thin films were grown directly on p-type Si(100) substrates for metal ferroelectric semiconductor field effect transistor (MFSFET) applications. Low temperature film growth and post rapid thermal anneal (RTA) treatments improved the leakage current of films while keeping other properties almost the same as high substrate temperature grown samples. We reduced the leakage current density of LiNbO3 films from 10−5 A/cm2 to 10−7 A/cm2 with RTA treatment. LiNbO3 MFS capacitors exhibited a breakdown electric field of greater than 500 kV/cm. RTA treatment above 600°C converted LiNbO3 films from amorphous to polycrystalline states with ( 0 1 2 ), ( 0 1 5 ), ( 0 2 2 ), and ( 0 2 3 ) planes. The polycrystalline LiNbO3 MFS capacitors illustrated the ferroelectric switching characteristics with a memory window ranging from 0.6 to 1.9 V. We obtained a remanent polarization of 2.74 μC/cm2 and a coercive field of 170 kV/cm using the LiNbO3 MFS capacitors.

산소플라즈마 전처리된 Polyethylene Naphthalate 기판 위에 증착된 ZnO:Ga 투명전도막의 특성

Transparent conducting oxide (TCO) films are widely used for optoelectronic applications. Among TCO materials,zinc oxide (ZnO) has been studied extensively for its high optical transmission and electrical conduction. In this study, the effectsof O2 plasma pretreatment on the properties of Ga-doped ZnO films (GZO) on polyethylene naphthalate (PEN) substrate werestudied. The O2 plasma pretreatment process was used instead of conventional oxide buffer layers. The O2 plasma treatmentprocess has several merits compared with the oxide buffer layer treatment, especially on a mass production scale. In this process,an additional sputtering system for oxide composition is not needed and the plasma treatment process is easily adopted as anin-line process. GZO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesionbetween the PEN substrate and the GZO film, the O2 plasma pre-treatment process was used prior to GZO sputtering. As theRF power and the treatment time increased, the contact angle decreased and the RMS surface roughness increased significantly.It is believed that the surface energy and adhesive force of the polymer surfaces increased with the O2 plasma treatment andthat the crystallinity and grain size of the GZO films increased. When the RF power was 100W and the treatment time was120 sec in the O2 plasma pretreatment process, the resistivity of the GZO films on the PEN substrate was 1.05×10-3Ω-cm,which is an appropriate range for most optoelectronic applications.

Improving Efficiency of Low Cost EFG Ribbon Silicon Solar Cells by Using a SOD Method

The high cost of crystalline silicon solar cells has been considered as one of the major obstacles to their terrestrial applications. Spin on doping (SOD) is presented as a useful process for the manufacturing of low cost solar cells. Phosphorus (P509) was used as an n-type emitters of solar cells. N-type emitters were formed on p-type EFG ribbon Si wafers by using a SOD at different spin speed (1,000~4,000 rpm), diffusion temperatures (), and diffusion time (5~30 min) in atmosphere. With optimum condition, we were able to achieve cell efficiency of 14.1%.

Properties of the ZnS Thin Film Buffer Layer by Chemical Bath Deposition Process with Different Solution Concentrations and Deposition Time

In this study, chemical bath deposition method was used to grow Zinc sulfide(ZnS) thin films from NH3/SC(NH2)2/ZnSO4 solutions at 90°C. ZnS thin films have been prepared onto ITO glass. The concentrations of ZnSO4 and NH were varied while the concentration of Thiourea was fixed in 0.52 M. Structural, optical, electrical characteristic of ZnS thin films were measured. The physical and optical properties of different ZnS thin films were influenced severely by the concentration of the two reacting chemicals. The optimal concentration of ZnSO4 and NH3 was 0.085 M and 1.6 M, respectively.

Improvement of Efficiency of Cu(In x ,Ga 1-x )Se 2 Thin Film Solar Cell by Enhanced Transparent Conductive Oxide Films

In this study, Sputtering method was used to grow Al-dopes ZnO films on a CIGS absorber layer, in order to examine the effect of TCO on properties of CIGS solar cell devices. Structural, electrical and optical properties were investigated by varied thickness of Al-dopes ZnO films. Also, relation to the application as a window layer in CIGS thin film solar cell were studied. It was found that the electrical and structural properties of ZnO:Al film improved with increasing its thickness. However, the optical properties degraded. Jsc of the fabricated CIGS based solar cells was significantly influenced by the variation of the ZnO:Al window layer thickness. Because ZnO:Al window layer is one of the Rs factors in CIGS solar cell. Rs has the biggest influence on efficiency characteristic. In order to obtain high efficiency of CIGS solar cell, ZnO:Al window layer should be fabricated with electrically and optically optimized.

Growth and Resistance Properties of Carbon Nanowall According to the Variation of Reaction Gas

Graphite electrodes are used for secondary batteries, fuel cells, and super capacitors. Research is underway to increase the reaction area of graphite electrodes. In this study, we have investigated the growth properties of carbon nanowall (CNW) according to the ingredient of gas. Microwave plasma enhanced chemical vapor deposition (MPECVD) system was used to grow CNW on Si substrate with a variety of the reaction gas. The planar and vertical growth conditions of the grown CNWs according to the ingredient of the gas were characterized by a field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The electrical characteristics of CNWs were analyzed using a 4-point probe.

Fabrication of metal-coated carbon nanowalls synthesized by microwave plasma enhanced chemical vapor deposition.

In this study, the coating of synthesized carbon nanowalls (CNWs) with various metal layers (Ni, Cu, and W) was investigated. CNWs were synthesized by microwave plasma enhanced chemical vapor deposition (PECVD) with a methane (CH4) and hydrogen (H2) gas mixture on a p-type Si wafer, and then coated with metal films (Ni, Cu, and W) using an RF magnetron sputtering system with four-inch targets. Different sputtering times (5, 10, 20, and 30 min) were established to obtain different thicknesses of the metal layers with which the CNWs were coated. Field emission scanning electron microscopy (FE-SEM) was used to examine the cross-sectional and planar conditions of the CNWs, and energy dispersive spectroscopy (EDS) was used to analyze the CNW elements. The FE-SEM analysis of the cross-sectional and planar images confirmed that the metal layers were synthesized to a depth of 0.5 μm from the surfaces of the CNWs, and to a greater depth at the ends of the CNWs, irrespective of the deposition time and the metal species. The resistivity of the as-deposited CNWs appeared as 4.18 x 10(-3) Ω cm; that of the metal-coated CNWs was slightly lower; and that of the Ni-coated CNWs was the lowest (1.74 x 10(-3) Ω cm). The mobility of the metal-coated CNWs was almost unchanged, and that of the as-deposited CNWs was 1.23 x 10(3) cm2 V(-1) s(-1).

A Study on Selenization of Cu-In-Ga Precursors by Cracked Selenium

In this study, (CIGS) thin films were prepared on the Mo coated soda-lime glass by the DC magnetron sputtering and a subsequent selenization process. For the selenization process, selenization rapid thermal process(RTP) with cracker cell, which was helpful to smaller an atomic of Se, was adopted. To make CIGS layer, they were then annealed with the cracked Se. Based on this selenization method, we made several CIGS thin film and investigated the effects of In deposition time, and selenization time. Through x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM), it is found that the Mo/In/CuGa structure and the high sputtering power shows the dominant chalcopyrite structure and have a uniform distribution of the grain size. The CIGS films with the In deposition time of 5 min has the best structure due to the smooth surface. And CIGS films with the selenization time of 50 min show good crystalline growth without any voids.