X-ray Amorphous P-type Conductive Oxide; ZnRh 2 O 4
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X-ray Amorphous P-type Conductive Oxide; ZnRh2O4 Satoru Narushima,1 Hiroshi Mizoguchi,2 Hiromichi Ohta,2 Masahiro Hirano,2 Ken-ichi Shimizu,3 Kazushige Ueda,1 Toshio Kamiya,1,2 and Hideo Hosono1,2 1 Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8503, JAPAN 2 Transparent ElectroActive Materials, Exploratory Research for Advanced Technology, Japan Science and Technology Corporation, KSP C-1232, 3-2-1 Sakado, Takatsu-ku, Kawasaki 213-0012, JAPAN 3 Keio University, Hiyoshi, Yokohama 233-0061, Japan ABSTRACT An amorphous p-type conductive oxide semiconductor was created based on a mother crystalline material, a p-type conductive ZnRh2O4 spinel. The amorphous film of ZnRh2O4 was deposited by an rf sputtering method. Seebeck coefficient was positive, +78 µVK-1, indicating that major carrier is a positive hole. A moderate electrical conductivity (2 S cm-1 at room temperature) for a p-type semiconductor was observed. Optical band gap was estimated to be 2.1 eV. P-n junction diodes with a structure of Au / a-ZnRh2O4 / a-InGaZnO4 / ITO fabricated on glass substrates, operated with a good rectifying characteristics, a rectification current ratio at ± 5V of ~103. The threshold voltage was 2.1 eV, which corresponds to the band gap energy of the amorphous ZnRh2O4. This is the first discovery of a p-type amorphous oxide and the demonstration of p-n junction all composed of amorphous oxide semiconductors.
INTRODUCTION Amorphous semiconductor films have many process merits such as low temperature and large area deposition on any substrates including glass and plastic sheets1, in comparison with crystalline semiconductors. However, it was believed that the control of the conductivity is difficult in amorphous materials except for tetrahedral system represented by hydrogenated amorphous silicon (a-Si:H) because conventional tetrahedral and chalcogenaide-based semiconductors involve many defects, pinning the Fermi level unless hydrogenated. On the contrary, we have recently found a series of transparent amorphous oxide semiconductors based on our guiding principle for searching new semiconductor oxides,2 leading to the findings of a-AgSbO3 3 , a-2CdOּGeO2 4 , a-CdOּPbOx 5 and a-InGaO3(ZnO)m (m≤4). 6 A theoretical investigation has revealed that the electronic states in oxides are different from the conventional semiconductors, and that widely-spread metal s orbitails in the conduction band of these oxides form favorable electron transport paths. 7 However, all of these amorphous oxides exhibit n-type electrical conduction. That is, a p-type amorphous oxide has not been discovered. In crystalline oxides, a series of materials8 including SrCu2O29 and CuAlO210 was found to be transparent p-type semiconductors, and oxide p-n junctions were fabricated using these new materials. 11 However, the interface defects formed due to the lattice mismatching in heteroepitaxial junctions and grain boundaries in polycrystalline junctions deteriorate the device
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