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. ...

/pdf/a-comprehensive-review-of-zno-materials-and-devices-21a3zjadem.pdf

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

Research on improved amorphous silicon-based devices has focused on materials prepared at high temperatures and/or those grown under very reactive conditions. The use of these conditions for device applications requires the development of more robust transparent conductive oxide (TCO) substrates. A thin (<10 nm) ZnO coating on a SnOx-coated glass substrate could withstand RF (13.56 MHz) and very high frequency (VHF: 144 MHz) hydrogen plasma treatments; however, the TCO was strongly reduced by a higher density, higher energy electron cyclotron resonance (ECR) hydrogen plasma or a higher temperature. Ga-doped ZnO (GZO) TCO substrates exhibited greater resistance to hydrogen plasma induced reduction. RF magnetron sputter deposited crystalline GZO thin films were deposited and optimized at temperatures higher than 150°C on glass substrates. The electron mobility and the Ga doping efficiency were improved with increasing GZO deposition temperature. The performance of a-Si:H solar cells fabricated under standard conditions (~220°C) on these GZO substrates increased with increased GZO deposition temperature. The performance of a-Si:H solar cells prepared under more reactive and/or at higher deposition temperatures on 250°C deposited GZO was also examined. Both high temperature (280°C)-deposited narrow-bandgap a-Si:H(Ar) and ECR hydrogen plasma deposited a-Si:H(Cl) based solar cells were significantly improved using high temperature deposited GZO substrates.

Optimization of Transparent Conductive Oxide for Improved Resistance to Reactive and/or High Temperature Optoelectronic Device Processing

Effects of a lattice-matched buffer layer on growth, structure, and transport properties of ZnO thin films were examined using a homologous series layered compound, InGaO3(ZnO)5 (IGZO5). High-quality single-crystalline IGZO5 layers were fabricated on yttria-stabilized zirconia (YSZ) (111) substrates by reactive solid-phase epitaxy. ZnO layers deposited on the IGZO5 buffer layers showed smooth and uniform surface morphologies compared to those deposited on YSZ (111) without the IGZO5 buffer layer. Then postgrowth annealing was examined to convert the ZnO surface to an atomically flat surface. When the IGZO5 buffer layer was used, the annealing temperature was reduced from 1000 to 700 °C, which was attributable to the smooth surface morphology and good lattice matching of the buffer layer. The annealed films exhibited rather large Hall mobilities 73−82 cm2 (Vs)-1, which are larger than those reported for epitaxial ZnO films fabricated at similar temperatures with similar thicknesses. Cross-sectional high-re...

Self-Adjusted, Three-Dimensional Lattice-Matched Buffer Layer for Growing ZnO Epitaxial Film: Homologous Series Layered Oxide, InGaO3(ZnO)5

Effects of O2− or OH− ion incorporation on the cage geometry in 12CaO·7Al2O3 (C12A7) crystals are examined by the maximum entropy method (MEM)/Rietveld analyses of synchrotron powder X-ray diffract...

Anion Incorporation-induced Cage Deformation in 12CaO·7Al2O3 Crystal

Optical evidence for quantization in transparent amorphous oxide semiconductor superlattice

LaCuOSe is a wide band gap p-type semiconductor in which high density positive holes can be doped to exhibit degenerate conduction. These features should allow room-temperature ferromagnetism in a dilute magnetic semiconductor (DMS), which follows a theoretical prediction [T. Dietl et al., Science 287, 1019 (2000)], yet to be realized. A weak ferromagnetic response is observed in both bulk and thin epitaxial film samples of Mn-doped LaCuOSe with hole concentrations of ∼1020cm−3. However, the observed small magnetization (μB per Mn ion of less than unity) is reasonably explained by the inclusion of 0.2mol% of LaMnO3 and 0.1mol% of Mn3O4, which were quantitatively analyzed in the bulk sample using highly sensitive x-ray diffractometry, i.e., Mn-doped LaCuOSe did not exhibit ferromagnetism due to the low solubility limit of Mn in LaCuOSe (<0.5mol%). This result demonstrates the importance of complementary characterization using both thin film and bulk samples for studying DMSs.

Toshio Kamiya

Papers

Optimization of Transparent Conductive Oxide for Improved Resistance to Reactive and/or High Temperature Optoelectronic Device Processing

Self-Adjusted, Three-Dimensional Lattice-Matched Buffer Layer for Growing ZnO Epitaxial Film: Homologous Series Layered Oxide, InGaO3(ZnO)5

Anion Incorporation-induced Cage Deformation in 12CaO·7Al2O3 Crystal

Optical evidence for quantization in transparent amorphous oxide semiconductor superlattice

Magnetic and carrier transport properties of Mn-doped p-type semiconductor LaCuOSe: An investigation of the origin of ferromagnetism