There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers1. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H)2,3,4,5 and organic semiconductors2,6,7,8,9,10 have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven organic light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temperature and device performance. Here, we propose to solve this problem by using a novel semiconducting material—namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO)—for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temperature and exhibits Hall effect mobilities exceeding 10 cm2 V-1 s-1, which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit saturation mobilities of 6–9 cm2 V-1 s-1, and device characteristics are stable during repetitive bending of the TTFT sheet.

Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors

We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temperature (Tc) exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.

Iron-Based Layered Superconductor La[O1-xFx]FeAs (x = 0.05−0.12) with Tc = 26 K

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

Polycrystalline silicon (poly-Si) photovoltaic devices were fabricated from SiF 4 , H 2 and SiH 4 gas mixtures using very high frequency (100 MHz) chemical vapor deposition (VHF CVD). The gas flow rate and the SiF 4 /H 2 /SiH 4 ratio were optimized for low temperature, device quality poly-Si growth. The n-layers used for the n/i/Pt Schottky diodes and n/i/p solar cells were deposited at 300°C and i-layers at 100–300°C to provide a seed layer for subsequent i-layer growth. The open circuit voltage increased with i-layer growth temperature in the n/i/Pt Schottky diodes. However, the optimal fill factor (FF) occurred at a ∼200°C i-layer growth temperature. The FF decreased at temperatures >250°C. The best solar cells had short circuit current of 24 mA/cm 2 and energy conversion efficiency of 6.22%. Also, it was possible to prepare high efficiency solar cells at relatively high growth rates, 0.5 nm/s, by optimizing the SiH 4 flow rate.

Microstructure and photovoltaic properties of low temperature polycrystalline silicon solar cells fabricated by VHF-GD CVD using fluorinated gas

InFe1−xTixO3+x∕2 (0.5⩽x⩽0.75) has an interesting crystal structure for a magnetic semiconductor because it is composed of In–O layers and (Fe,Ti)–O layers in which the former may work as the electron transport layers, while the latter may work as the magnetic layers. Herein we report epitaxial film growth of InFe0.33Ti0.67O3.33 (IFTO) using pulsed laser deposition and post-annealing. High-quality epitaxial IFTO films with an atomically flat terrace-and-step structure are fabricated on (0001) sapphire substrates. IFTO is an indirect transition-type semiconductor with an optical band gap of ∼2.9eV. The room-temperature electrical conductivity is less than 10−8Scm−1. Carrier doping by aliovalent ion addition, hydrogen reduction, and so on did not generate more free carriers, which may be due to the localized nature of the unoccupied states in IFTO. The Fe ions have the high-spin configuration of Fe3+ and an antiferromagnetic interaction is observed between the Fe3+ ions. A spin-glass state is observed at ⩽5K.

Toshio Kamiya

Papers

Microstructure and photovoltaic properties of low temperature polycrystalline silicon solar cells fabricated by VHF-GD CVD using fluorinated gas

Epitaxial film growth, optical, electrical, and magnetic properties of layered oxide In3FeTi2O10

Effect of Intentional Chemical Doping on Crystallographic and Electric Properties of the Pyrochlore Bi2Sn2O7

Double Charge Polarity Switching in Sb‐Doped SnSe with Switchable Substitution Sites

Microstructure control of very thin polycrystalline silicon layers on glass substrate by plasma enhanced CVD