Won-Ho Son

Characteristics of Hydrogenated Amorphous Silicon Germanium Thin Film Solar Cells by GeH4 Flow Rate

Hydrogenated amorphous silicon germanium alloys thin films had been grown by PECVD method. This article shows characteristics of hydrogenated amorphous silicon germanium thin film solar cells with GeH4 flow rates. The optical bandgap of hydrogenated amorphous silicon germanium alloy decreased from 1.78 eV - 1.54 eV with increasing in GeH4 flow rate from 0 sccm – 100sccm. The various values of Voc, Jsc, FF, and conversion efficiency were measured by the solar simulator. These results show that the conversion efficiency of the a-SiGe:H solar cells was very high when the GeH4 flow rate was 60 sccm.

Hydrogenated amorphous silicon thin film solar cell with buffer layer of DNA-CTMA biopolymer

The characteristics of nip-type a-Si:H thin film solar cells based on DNA-CTMA biopolymer was investigated. The DNA-CTMA was used as the buffer layer in nip-type a-Si:H solar cell. The Eopt of the DNA-CTMA biopolymer was measured with UV-VIS spectrometer. The Eopt of DNA-CTMA was determined as 3.96 eV by the plot of (Ahν)2 versus hν. All films of amorphous materials were deposited by PECVD method. The solar cell with a simple structure of glass/ITO/n-a-Si:H/i-a-Si:H/p-a-Si:H/DNA-CTMA/Al was fabricated. The various values of Voc, Jsc, FF, and conversion efficiency η were measured under 100 mW/cm2 (AM 1.5) solar simulator irradiation. Consequently, the resulting in solar cell showed an enhancement in conversion efficiency η compared to conventional nip-type a-Si:H solar cell without buffer layer of DNA-CTMA biopolymer.

The Optical Properties of a-Si:H/a-SiGex:H Superlattice Structure to Apply Intrinsic Layer in Solar Cell

The hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon-germanium (a-SiGe:H) alloys have been prepared by the plasma enhanced chemical vapor deposition (PECVD) method. The films were grown on corning #1737 glass from the gas mixture of silane and germane. Superlattice thin films consisted of a-Si:H/a-SiGe:H multilayer structure. The UV-VIS Spectrometer analysis of a-SiGex:H alloys and superlattices thin films showed that the bandgap absorption spectra of a-SiGex:H alloys shift to lower photon energy with an increase in the GeH4 flow rate [0–300 sccm] and various a-Si:H [2−10 nm]/a-SiGex:H [2 nm] thickness. The optical bandgap had decreased by between 1.24∼1.71 eV in regards to a-SiGe:H and superlattice thin films.

Improvement of the Electrical Characteristics of a-Si:H TFTs Using the Phosphorus Doping in the Active Layer

This paper suggests a method of phosphorus doping in the active layer to improve the electrical characteristics of hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT). Phosphorus doping in the active layer of a-Si:H was performed by the deposition of a-Si:H through the addition of phosphine gas by plasma enhanced chemical vapor deposition (PECVD). We confirmed that the electrical characteristics of phosphorus doped a-Si:H TFT were improved compared to those of conventional a-Si:H TFT to the extent that the field effect mobility and off current were 0.44 cm2/V•s and 1.53 × 10−12 cm2 when phosphorus was doped by 1 sccm. We investigated the sheet resistance (Rs), root-mean-square roughness (RMS) and density of state (DOS) to demonstrate the improved electrical characteristics. From the results, we confirmed that phosphorus doping in the active layer supplies the electron to use dopant in the channel as well as leads to an improvement of the DOS and higher quality in a-Si:H.

Effect of gradually increasing germane flow rate during the deposition on the performance of a-SiGe:H solar cell

In this paper, we fabricated a hydrogenated amorphous silicon-germanium (a-SiGe:H) thin film solar cell with gradually increasing GeH4 flow rate in order to absorb long wavelength of solar spectrum without stacked structures such as tandem or triple junctions. The thin film solar cell with the a-SiGe:H in its intrinsic layer deposited using 13.56 MHz radical-assisted/plasma-enhanced chemical vapor deposition (RA/PECVD) was characterized according to several conditions of gradually varying GeH4 flow rate. Under AM 1.5 G conditions, open-circuit voltage (VOC), short-circuit current density (JSC), fill factor and efficiency have been investigated. Also, external quantum efficiency (EQE) was measured. As a result, the best value of VOC, JSC and fill factor were 0.42 V, 24.16 mA/cm2 and 0.52, respectively. Efficiency of the solar cell was up to 5.3%, and EQE in the wavelength range of 400–800 nm occupied most of photon absorption.

The Effects of Phosphorus Doping in the a-Si:H and a-SiN:H on the Electrical Characteristics of a-Si:H TFT

The effect of phosphorus doping in hydrogenated amorphous silicon (Si:H) and hydrogenated amorphous silicon nitride (a-SiN:H) for the electrical performances of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) was studied. The phosphorus-doped layers in the a-Si:H and a-SiN:H with various concentrations were deposited by plasma-enhanced chemical vapor deposition (PECVD). We measured the electrical characteristics of a-Si:H TFTs fabricated by one or both phosphorus doping in a-Si:H and a-SiN:H, and then compared these results to conventional a-Si:H TFT. The sheet resistance and surface roughness of the a-SiN:H layers with various phosphorus doping concentrations were investigated to verify the effects of phosphorus doping on the electrical characteristics of the a-Si:H TFTs.

Effects of RF Power and Substrate Temperature on the Performance of Thin-Film Silicon Solar Cells

This article shows the characteristics of pin-type solar cells with different radio frequency (RF) power and substrate temperature (Ts). All films of amorphous materials were deposited by 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) method using a mixture of silane (SiH4) and hydrogen (H2). The SiH4 gas was used as a gas source and the doping process was done by gas admixture of 3% diborane (B2H6) diluted in hydrogen (H2) and 1% phosphine (PH3) diluted in H2 for p- and n-layer, respectively. The effects of deposited parameters on the characteristics of a-Si:H films have been investigated by field emission scanning electron microscope (FE-SEM), dark- and photo-conductivity (σd and σph) measurement and ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometer, respectively. The results showed that the deposition rate of a-Si:H films increased with increasing of RF power and Ts. The optical band gap (Eopt) of a-Si:H films was increased with increasing of RF power from 20–60 Watt, and slightly decreased at RF power of 60–100 Watt. The various values of open-circuit voltage (Voc), short-circuit current density (Jsc), and conversion efficiency were measured by the solar simulator. It was found that a-Si:H films deposited at RF power of 60 Watt and Ts of 200°C are better suited for thin-film silicon solar cell application.

Fabrication and Characteristics of a Varactor Diode for UHF TV Tuner Operated within Low Tuning Voltage

The width of depletion region in a varactor diode can be modulated by varying a reverse bias voltage. Thus, the preferred characteristics of depletion capacitance can obtained by the change in the width of depletion region so that it can select only the desirable frequencies. In this paper, the TV tuner varactor diode fabricated by hyper-abrupt profile control technique is presented. This diode can be operated within 3.3 V of driving voltage with capability of UHF band tuning. To form the hyperabrupt profile, firstly, p+ high concentration shallow junction with of junction depth and of surface concentration was formed using implantation source. Simulation results optimized important factors such as epitaxial thickness and dose quality, diffusion time of n+ layer. To form steep hyper-abrupt profile, Formed n+ profile implanted the source at Si(100) n-type epitaxial layer that has resistivity of and thickness of using p+ high concentration Shallow junction. Aluminum containing to 1% of Si was used as a electrode metal. Area of electrode was . The C-V and Q-V electric characteristics were investigated by using impedance Analyzer (HP4291B). By controlling of concentration profile by n+ dosage at p+ high concentration shallow junction, the device with maximum at -1.5 V and 21.5~3.47 pF at 0.3~3.3 V was fabricated. We got the appropriate device in driving voltage 3.3 V having hyper-abrupt junction that profile order (m factor) is about -3/2. The deviation of capacitance by hyper-abrupt junction with C0.3 V of initial capacitance is due to the deviation of thermal process, ion implantation and diffusion. The deviation of initial capacitance at 0.3 V can be reduced by control of thermal process tolerance using RTP on wafer.

Characteristics of a Double-Tube Structure for the Hydraulic WIM Sensor

Abstract A new hydraulic tube structure for WIM sensor of a new generation is presented in this paper. The double-tube structure has beendeveloped in order to improve the performance of the hydraulic load cell. The double-tube structure hydraulic element could be reducedby 46% in pressure changes according to temperature compared to a single-tube structure. In addition to the nonlinearity can be reducedby 67.19% at the same load condition. The hydraulic load cell shows an excellent linearity and measurement accuracy as the result ofthe static load test. Keywords: Double-tube, Hydraulic load cell, WIM sensor 1. INTRODUCTION Weight-In-Motion (WIM) sensor is used for measuring thedynamic load of a moving vehicle to estimate the correspondingstatic load of the vehicle [1,2]. WIM systems have very importantbenefits in traffic monitoring to reduce accident frequency rates, toreduce fuel consumption and to reduce pavement costs [3,4].Several kinds of WIM sensors have been developed and arecommercially available. A banding plate load cell, the mostcommonly used low-speed WIM sensor, is performed withrelatively high accuracy. However, the installation costs are high,and the accuracy is low in the vehicle traveling at high speed dueto the slow response time [5,6]. A piezoelectric sensor is low cost,but does not work properly at low speeds of less than 20 km/h[7,8]. So far, in spite of high accuracy, hydraulic load cell is usedfor the limited purposes, such as measuring the static load.Because of the pressure in the sensor is significantly changed bythe temperature and that has slow response time by using thecorrugated diaphragm. Therefore, the need for the development ofa new structure is required. In this paper, the proposed hydraulic load cell is composed ofa spring/hydraulic element and a single sensing element. Thehydraulic element was made by SUS304 as the double-tubestructure in order to reduce the pressure changes depending on thetemperature to improve accuracy and to speed up the responsetime. A sensing element detects a change in the internal pressureof the tube caused by an applied load.

Characteristics of a-SiC:H/a-SiGe:H hetero-junction thin film solar cells with and without a-Si:H buffer layer at the p/i interface

This article shows the characteristics on a-SiGe:H based solar cells with various structures. Based on these results, we proposed the a-SiC:H/a-SiGe:H hetero-junction thin film solar cells with a-Si:H buffer layer at the p/i interface to improve the performance of pin-type a-SiGe:H based solar cell. All films of amorphous materials were deposited by 13.56 MHz PECVD method. The effects of deposited parameters on the characteristics of a-SiC:H and a-SiGe:H films have been investigated by ultraviolet–visible–near infrared (UV–VIS–NIR) spectrophotometer. The various values of Voc, Jsc, FF and η were measured under 100 mW/cm2 (AM 1.5) solar simulator irradiation. In the proposed structure, we achieved a higher conversion efficiency than general a-SiGe:H solar cell and a-SiC:H/a-SiGe:H hetero-junction thin film solar cells without a-Si:H buffer layer at the p/i interface. Based on results obtained from this study, we discuss the roles of a-Si:H buffer layer in a-SiC:H/a-SiGe:H hetero-junction thin film solar cells.