Masaaki Kurita

P-type electrical conduction in transparent thin films of CuAlO2

Optically transparent oxides tend to be electrical insulators, by virtue of their large electronic bandgap (⩾3.1 eV). The most notable exceptions are doped versions of the oxides In2O3, SnO2 and ZnO—all n-type (electron) conductors—which are widely used as the transparent electrodes in flat-panel displays. On the other hand, no transparent oxide exhibiting high p-type (hole) conductivity is known to exist, whereas such materials could open the way to a range of novel applications. For example, a combination of the two types of transparent conductor in the form of a pn junction could lead to a ‘functional’ window that transmits visible light yet generates electricity in response to the absorption of ultraviolet photons. Here we describe a strategy for identifying oxide materials that should combine p-type conductivity with good optical transparency. We illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temperature p-type conductivity up to 1 S cm−1. Although the conductivity of our candidate material is significantly lower than that observed for the best n-type conducting oxides, it is sufficient for some applications, and demonstrates that the development of transparent p-type conductors is not an insurmountable goal.

Isotope Effect on Photoconductivity in Quantum Paraelectric SrTiO3

Photoconductivity and various photo-magnetotransport properties have been studied in quantum paraelectric SrTiO 3 crystals. SrTi 16 O 3 shows giant photoconductivity, as reported before. The photodoped carrier in the 16 O system is of electron type and has high mobility beyond 10 4 cm 2 V -1 s -1 at 5 K. Its number can reach the order of 10 15 cm -3 . In contrast, isotope-substituted SrTi 18 O 3 is not a good photoconductor. In addition, the photocarriers mobility in the 18 O sample is negligibly small. These results suggest a strong correlation between the quantum fluctuation and the giant photoconductivity in this quantum paraelectric system. In other words, the study of photocarrier dynamics is a novel approach to the investigation of quantum fluctuation in dielectric materials.

Excimer laser crystallization of amorphous indium–tin oxide thin films and application to fabrication of Bragg gratings

Abstract Amorphous (a-) indium–tin oxide (ITO) thin films were crystallized at ambient temperature by irradiation with KrF (248 nm) or ArF (193 nm) excimer laser pulses of ≥40 mJ/cm 2 per pulse. Electrical resistivity of the specimen at ∼300 K decreased from 5.9×10 −4 Ω cm to 2.7×10 −4 Ω cm upon laser crystallization. This decrease was due to the increase in the carrier concentration which arises from the occupation of In 3+ sites in the lattice with Sn 4+ upon crystallization. Photo-imprinted Bragg gratings of crystalline ITO thin films were successfully fabricated by irradiation of a-ITO thin films with the excimer laser pulses through a silica phase mask and subsequent chemical etching of the irradiated thin films utilizing the large differences in the etching rate between crystallized and amorphous ITOs.

Giant Photoconductivity in Quantum Paraelectric Oxides

Photoconductivity and photo-magneto-transport properties have been measured in quantum paraelectric SrTiO3 crystals. We have found a large isotope effect in the photocurrent value in this system. This isotope effect suggests an important contribution of the quantum fluctuations for the giant photoconductivity in the quantum paraelectric system.

High Carrier Mobility Coupled with Quantum Paraelectric Fluctuation

Photoconductivity and photo-magneto-transport properties have been measured in quantum paraelectric and ferroelectric SrTiO 3 crystals. We have found a large isotope effect on the conductivity of photo-carrier in this system. This isotope effect strongly suggests a close correlation between the quantum fluctuations and the giant photoconductivity in the quantum paraelectric system. Here we propose the possibility of the control of the carrier motion by using the external electric field. These results may become a key to understand the behavior of the carrier in the dense electric dipoles with so called as quantum fluctuation.