In this study, the effect of thickness on the Sn-doped β-Ga₂O₃ thin films was investigated. β-Ga₂O₃ is a next-generation material for power semiconductors and optoelectronics owing to its remarkable properties, such as an ultra-wide bandgap, excellent thermal and chemical stability, and large breakdown voltage. However, its inherently low conductivity can be limiting in applications that require high conductivity; therefore, improving the conductivity of β-Ga₂O₃ is important. In this study, Sn-doped β-Ga₂O₃ thin films with various thicknesses were deposited on β-Ga₂O₃ substrates. All the fabricated samples exhibited β-phase with a uniform and dense surface and transmittance of above 80% in the visible region. In particular, the 100 nm samples showed the highest carrier concentration and mobility and the lowest resistivity. Thus, these findings are expected to play an important role in improving the performance of devices by controlling the thickness of thin films.

Passivation quality is mainly governed by epitaxial growth of crystalline silicon wafer surface. Void-rich intrinsic a- Si:H interfacial layer could offer higher resistivity of the c-Si surface and hence a better device efficiency as well. To reduce the resistivity of the contact area, a modification of void-rich intrinsic layer of a-Si:H towards more ordered state with a higher density is adopted by adapting its thickness and reducing its series resistance significantly, but it slightly decreases passivation quality. Higher resistance is not dominated by asymmetric effects like different band offsets for electrons or holes. In this study, multilayer of intrinsic a-Si:H layers were used. The first one with a void-rich was a-Si:H(I₁) and the next one a-SiO_x:H(I₂) were used, where a-SiO_x:H(I₂) had relatively larger band gap of ~2.07 eV than that of a-Si:H (I₁). Using a-SiO_x:H as I₂ layer was expected to increase transparency, which could lead to an easy carrier transport. Also, higher implied voltage than the conventional structure was expected. This means that the a-SiO_x:H could be a promising material for a high-quality passivation of c-Si. In addition, the i-a-SiO_x:H microstructure can help the carrier transportation through tunneling and thermal emission.

We investigated the growth of Al_xGa_1-x)₂O₃ thin films on c-plane sapphire substrates that were grown by mist chemical vapor deposition (mist CVD). The precursor solution was prepared by mixing and dissolving source materials such as gallium acetylacetonate and aluminum acetylacetonate in deionized water. The [Al]/[Ga] mixing ratio (MR) of the precursor solution was adjusted in the range of 0~4.0. The Al contents of (Al_xGa_1-x)₂O₃ thin films were increased from 8 to 13% with the increase of the MR of Al. As a result, the optical bandgap of the grown thin films changed from 5.18 to 5.38 eV. Therefore, it was determined that the optical bandgap of grown (Al_xGa_1-x)₂O₃ thin films could be effectively engineered by controlling Al content.

SiGe thin films were deposited by remote plasma enhanced chemical vapor deposition (RPE-CVD) at 400℃ using SiH₄ or SiCl₄ and GeCl₄ as the source of Si and Ge, respectively. The growth rate and the degree of crystallinity of the fabricated films were characterized by scanning electron microscopy and Raman analysis, respectively. The optical and electrical properties of SiGe films fabricated using SiCl₄ and SiH₄ source were comparatively studied. SiGe films deposited using SiCl₄ source showed a lower growth rate and higher crystallinity than those deposited using SiH4 source. Ultraviolet and visible spectroscopy measurement showed that the optical band gap of SiGe is in the range of 0.88~1.22 eV.

TeO_x thin films were deposited at various O₂/Ar gas-flow ratios by a reactive RFmagneton sputtering technique from TeO₂ and Te targets. X-ray diffraction (XRD) results revealed that the TeO_x thin films were amorphous. The structure and chemical composition of the TeO_x thin films were investigated by fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The optical characteristics of the TeO_x thin films were investigated by an Ellipsometer and a UV-VIS-NIR spectrophotometer. According to the O₂/Ar gas-flow ratios, the atomic composition ratio of TeO_x thin films was divided into two regions(x=1-2, 2-3). Different optical characteristics were shown in each region. With an increasing O₂/Ar gas-flow ratio, the refractive index of the TeO_x thin films decreased and the optical bandgap of the films increased.

In this paper, the efficiency improvement of the heterojunction with intrinsic thin layer (HIT) solar cells is obtained by optimization process of p-type a-SiC:H as emitter. The optoelectronic of p-type a-SiC:H layers including the optical band-gap and conductivity under the methane gas content variation is conducted in detail. A significant increase in the Jsc by 1 mA/cm2 and Voc by 30 mV are attributed to enhanced photon-absorption due to broader band-gap of p-a-SiC:H and reduced band-offsets at p-side interface, respectively of HIT solar cells.

MgZnO has attracted a lot of attention for flexible device. In the flexible substrate, the crystalstructure of the thin films as well as the surface morphology is not good. Therefore, in this study, westudied on the effects of the oxygen pressure on the structure and crystallinity of Mg0.3Zn0.7O thin films deposited on PES substrate by using pulsed laser deposition. We used X-ray diffraction and atomic forcemicroscopy in order to observe the structural characteristics of Mg0.3Zn0.7O thin films. The crystallinity ofMg0.3Zn0.7O thin films with increasing temperature was improved, Grain size and RMS of the films wereincreased. UV-visible spectrophotometer was used to get the band gap energy and transmittance. Mg0.3Zn0.7O thin films showed high transmittance over 90% in the visible region. As increased workingpressure from 30 mTorr to 200 mTorr, the bandgap energy of Mg0.3Zn0.7O thin film were decreased from3.59 eV to 3.50 eV.

The ZnO thin films doped with Ga and Ge (GZO:Ge) were prepared on glass substrate using RF sputtering system. Structural, morphological and optical properties of the films deposited in different temperatures were studied. Proportion of the element of using target was 97 wt% ZnO, 2.5 wt% Ga and 0.5 wt% Ge with 99.99% highly purity. Structural properties of the samples deposited in different temperatures with 200 w RF power were investigated by field emission scanning electron microscopy, FE-SEM images and x-ray diffraction XRD analysis. Atomic force microscopy, AFM images were able to show the grain scales and surface roughness of each film rather clearly than SEM images. it was showed that increasing temperature have better surface smoothness by FE-SEM and AFM images. Transmittance study using UV-Vis spectrometer showed that all the samples have highly transparent in visible region (300∼800 nm). In addition, it can be able to calculate bandgap energy from absorbance data obtained with transmittance. The hall resistivity, mobility, and optical band gap energy are influenced by the temperature.

Gallium nitride (GaN), wide bandgap semiconductor, has attracted much attention because they are projected to have much better performance than silicon. In this paper, effects of design parameters change of GaN power static induction transistor (SIT) on the electrical characteristics (breakdown voltage, on resistance) were analyzed by computer simulation. According to the analyzed results, the optimization was performed to get power GaN SIT that has 600 V class breakdown voltage. As a result, we could get optimized 600 V class power GaN SIT that has higher breakdown voltage and lower On resistance with a thin (a several micro-meters) thickness of the channel layer.