Showing papers by "Junsin Yi published in 2008"

RIE texturing optimization for thin c-Si solar cells in SF6/O2 plasma

Abstract: Dry etching plasma parameters were optimized for texturing single crystalline thin silicon solar cells and hence for high efficiency. In reactive ion etching (RIE) texturing, a low etch depth (~2 µm) was obtained compared with the etch depth that occurred in the wet chemical texturing process. For the flow ratios (SF6/O2) of 2 and 3, needle-like and cylindrical type structured surfaces were obtained. In the RIE process, the effects of working pressure, flow ratio, and etching time on reflectance and electrical properties of single crystalline silicon solar cells were investigated. The textured c-Si wafer with needle-like structure has good antireflectance behaviour. The interface defect density (Dit) in these textured silicon wafers increased with etching time. But an improvement in the reduction of interface trap density was observed through the annealing effect. Single crystalline solar cells with cylindrical type texture have higher values for open circuit voltage, short circuit current and efficiency in spite of a higher reflectance as compared with those needle-like structures. It is observed that the optimized SF6/O2 based chemistry in the RIE method is more suitable for thin crystalline silicon solar cells instead of the conventional wet texturization processes.

Mixed SnO2/TiO2 included with carbon nanotubes for gas-sensing application

Abstract: TiO2 and SnO2 are the well-known sensing materials with a good thermal stability of the former and a high sensitivity of the latter. Carbon nanotubes (CNTs) have also gas sensing ability at room temperature. CNTs-included SnO2/TiO2 material was a new exploration to combine the advantages of three kinds of materials for gas-sensing property. In this work, a uniform SnO2/TiO2 solution was prepared by the sol–gel process with the ratio 3:7 in mole. The CNTs with contents in the range of 0.001–0.5 wt% were dispersed in a mixed SnO2/TiO2 matrix by using an immersion-probe ultrasonic. The SnO2–TiO2 and the CNTs-included SnO2–TiO2 thin films were fabricated by the sol–gel spin-coating method over Pt-interdigitated electrode for gas-sensor device fabrication and they were heat treated at 500 °C for 30 min. FE-SEM and XRD characterizations indicated that the inclusion of CNTs did not affect the particle size as well as the morphology of the thin film. The sensing properties of all as-fabricated sensors were investigated with different ethanol concentrations and operating temperatures. An interesting sensing characteristic of mixed SnO2/TiO2 sensors was that there was a two-peak shape in the sensitivity versus operating temperature curve. At the region of low operating temperature (below 280 °C), the hybrid sensors show improvement of sensing property. This result gives a prospect of the stable gas sensors with working temperatures below 250 °C.

A new vapor texturing method for multicrystalline silicon solar cell applications

Abstract: Multicrystalline silicon (mc-Si) solar cell fabrication is still a key issue, due to its cost effectiveness compared to crystalline silicon (c-Si). In our present work, a new technique called vapor texturing (VT) is adopted, to achieve effective texturing of mc-Si. Saw damage removal with texturing (SDRWT) using acidic solution was performed on p-type mc-Si wafers with resistivity 0.5–2 Ω cm and thickness 210 μm, using HF:HNO3:CH3COOH:DI water in the ratio 8:21:10:8, for 3 min. An etching depth of about 4 μm is achieved on both sides of mc-Si wafers. The SDRWT-treated mc-Si wafers were vapor textured again by HF:HNO3 in the ratio 7:3, with 8 g of Si. The average reflectance of SDRWT-treated-only and SDRWT with vapor textured mc-Si wafers was 22.16 and 6.5%, respectively. The sheet resistance of SDRWT-treated-only and SDRWT with vapor textured mc-Si wafers was 88 and 50 Ω/□, respectively, after phosphorous doping. Subsequent to effective passivation, a sheet resistance of about 45 Ω/□ was achieved for both SDRWT-treated-only and SDRWT with vapor textured wafers. The effective minority carrier lifetime after vapor texturing and SiNx deposition is about 41.35 μs. Based on SEM analysis, surface morphology shows clear changes after each process.

Embedded LTPS flash cells with oxide-nitride-oxynitride stack structure for realization of multi-function mobile flat panel displays

Abstract: In this paper, embedded flash (eFlash) cells were fabricated for realization of multi-functions, such as systems on panels (SOPs) and threshold voltage (VTH) stabilization of flat panel displays (FPDs). Fabrication was via low temperature polycrystalline silicon (LTPS) thin film transistor (TFT) technology and an oxide–nitride–oxynitride (ONOn) stack structure on glass. Poly-silicon (poly-Si) on glass, which was annealed via an excimer laser, has a very rough surface. To fabricate LTPS eFlash cells on glass with a very rough poly-Si surface, plasma-assisted oxynitridation was performed; nitrous oxide (N2O) served as a reactive gas. LTPS eFlash cells have excellent TFT electrical properties, such as VTH, a high On/Off current ratio and a low sub-threshold swing (S). The results demonstrate that eFlash cells fabricated on glass with a rough silicon surface, via an ONOn stack structure, have switching characteristics suitable for data storage, such as a low operating voltage (<±10 V) suitable for mobile FPDs, a threshold voltage window, ΔVTH, which exceeds 2.3 V, between the programming and erasing (P/E) states, over a period of 10 years, and the capacity to retain the initial ΔVTH over a period of 105 P/E operations.

Preparation and characterization of sprayed In2O3:Mo films

Abstract: Transparent conducting oxides (TCO) play a major role in the area of thin film photovoltaics, flat panel displays, organic light emitting diodes and other optoelectronic devices In order to improve the performance of a device, the TCO should have good optical transmittance as well as conductivity In the present study, In2O3:Mo films have been grown by an economic and simple spray pyrolysis method with different molybdenum doping concentrations that vary in the range, 0–12 at% at a substrate temperature of 400 °C The structural and morphological, electrical and optical behaviour of the as-grown layers were studied All the deposited layers showed a body-centered cubic structure with a strong (222) orientation In2O3:Mo films grown with Mo-concentration of 60 at% had the maximum grain size of 90 nm The average optical transmittance of the films was >85% in the visible region The change of grain size, electrical resistivity, carrier mobility and density, optical band gap and figure of merit with doping concentration was reported and discussed (© 2008 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)

Characterization of MONOS nonvolatile memory by solid phase crystallization on glass

Abstract: Solid phase crystallization (SPC) is carried out because of the best uniformity among the various crystallization methods. SPC poly-Si nonvolatile memory (NVM) is expected superior memory property in terms of stable reliability. This paper presents electrical properties of SPC poly-Si NVM on glass. Nonvolatile memory is an ideal portable storage device due to its characteristics of low-power consumption and compact size. Metal/oxide/nitride/oxide/silicon (MONOS) structure memory was fabricated on glass. Silicon oxynitride (SiO x N y ) layer grown by nitrous oxide plasma served as a carrier tunnel layer, silicon nitride (SiN x ) as charge trap region and silicon dioxide (SiO 2 ) for blocking oxide were deposited to fabricate NVM on SPC poly-Si. SiO x N y , SiN x , and SiO 2 films were deposited by using inductively coupled plasma chemical vapor deposition (ICP-CVD). Electrical properties of NVM on glass were analyzed gate voltage–drain current ( V G – I D ) and charge retention property. We obtained the NVM device with the programming voltage of − 12 V, erasing of 11 V, and fast programming/erasing (P/E) time of 1 ms. It has a threshold voltage window memory of about 3.7 V and it still keep a wide threshold voltage window of 2.3 V after 10 years.

Fabrication of textured silicon solar cell using microlens as anti-reflection layer

Abstract: This paper presents facile, reproducible soft-lithographic technique for fabricating textured crystalline silicon solar cell with hexagonally close-packed hemispherical arrays using ordered polymeric microspheres Close-packed monolayers of polymer microspheres were deposited on flat cleaned glass substrate using spin-casting technique The relief structure of highly ordered microspheres successfully generated their negative replica of elastomers Hemispherical microlens arrays were molded by dispensing and curing liquid ultraviolet-curable photopolymers into the negative replica on crystalline silicon solar cell module Sub-micrometer scaled microlens with uniform, cleaned surface morphology were easily reproduced by using the prepared molds, without multi-step engineering processes The microlens-coated crystalline silicon solar cell showed additional increment of 1% in solar cell efficiency, compared to that of SiNx anti-reflection coated one, as well as remarkable decrease of reflectance in SiNx-uncoated solar cell