Motoki Takahara

Epitaxial growth of β-FeSi2 thin films on Si(111) substrates by radio frequency magnetron sputtering and their application to near-infrared photodetection

β-FeSi2 thin films were epitaxially grown on p-type Si(111) substrates at a substrate temperature of 560 °C and Ar pressure of 2.66 × 10−1 Pa by radio-frequency magnetron sputtering (RFMS) using a sintered FeSi2 target, without postannealing. The resultant n-type β-FeSi2/p-type Si heterojunctions were evaluated as near-infrared photodiodes. Three epitaxial variants of β-FeSi2 were confirmed by X-ray diffraction analysis. The heterojunctions exhibited typical rectifying action at room temperature. At 300 K, the heterojunctions showed a substantial leakage current and minimal response for irradiation of near-infrared light. At 50 K, the leakage current was markedly reduced and the ratio of the photocurrent to dark current was considerably enhanced. The detectivity at 50 K was estimated to be 3.0 × 1011 cm Hz1/2/W at a zero bias voltage. Their photodetection was inferior to those of similar heterojunctions prepared using facing-target direct-current sputtering (FTDCS) in our previous study. This inferiority is likely because β-FeSi2 films prepared using RFMS are located in plasma and are damaged by it.

XRD Investigation of the Crystalline Quality of Sn Doped β-Ga2O3 Films Deposited by the RF Magnetron Sputtering Method

For the purpose of increasing the conductivity of β-Ga2O3 films, Sn doping in the β-Ga2O3 films has been explored using co-sputtering. Growth of β-Ga2O3 was confirmed by the XRD pattern for the undoped sample. However, it is shown that the Ga2O3 phase is transformed from the β to the γ phase by Sn doping, because of the increase of the phase transition temperature from the γ to the β phase. To improve the crystalline quality, additional annealing at 900°C for 60 min is performed to the Sn doped film. The XRD peaks corresponding with β-Ga2O3 could be confirmed after the additional annealing.

Electric properties of carbon-doped n-type β-FeSi2/p-type Si heterojunction diodes

Motoki Takahara*, Tarek M. Mostafa, Ryuji Baba, Suguru Funasaki, Mahmoud Shaban, Nathaporn Promros, and Tsuyoshi Yoshitake 1Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580, Japan 2Department of Electrical Engineering, Aswan Faculty of Engineering, Aswan University, Aswan 81542, Egypt 3Department of Physics, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang, Chalongkrung Road, Bangkok 10520, Thailand

Epitaxial growth of n-type β-FeSi thin films on p-type Si(111) substrates by radio-frequency magnetron sputtering and rectifying action of heterojunctions

Tarek M. Mostafa, Motoki Takahara, Ryuji Baba, Suguru Funasaki, Mahmoud Shaban*, Nathaporn Promros**, Aki Tominaga, Maiko Nishibori, and Tsuyoshi Yoshitake*** 1Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580, Japan 2Department of Electrical Engineering, Aswan Faculty of Engineering, Aswan University, Aswan 81542, Egypt 3Department of Physics, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand 4Research Center for Synchrotron Light Applications, Kyushu University, Kasuga, Fukuoka 816-8580, Japan

Improvement of the Crystalline Quality of β-Ga2O3 Films by High-Temperature Annealing

For the purpose of improving the crystalline quality of undoped and Si doped β-Ga2O3 films, high temperature annealing at 900°C was performed. The crystalline quality of the films investigated using scanning electron microscopy and X-ray diffraction. Also the conductivity of the films is compared before and after the annealing. After the 900°C annealing, the XRD peaks intensity corresponding to β-Ga2O3 is increased. This result indicates that the crystalline quality improves by the high temperature annealing.