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

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 into terahertz technology is now receiving increasing attention around the world, and devices exploiting this waveband are set to become increasingly important in a very diverse range of applications. Here, an overview of the status of the technology, its uses and its future prospects are presented.

Cutting-edge terahertz technology

Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

Recent developments of zinc oxide based photocatalyst in water treatment technology: A review

Molecular beam epitaxial growth of wide bandgap ZnMgO alloy films on (111)-oriented si substrate toward UV-detector applications

The authors propose a new structure of ZnO∕ZnMgO field-effect transistors (FETs) for demonstrating high-performance capability of ZnO-based FETs. A very thin (2nm) ZnMgO cap layer is used for forming a hetero-metal-insulator-semiconductor (hetero-MIS) gate structure together with a 50-nm-thick Al2O3 gate dielectric. The 1-μm-gate device showed a complete FET operation and an extrinsic transconductance of as high as 28mS∕mm and an effective mobility of 62cm2∕Vs. The high effective mobility maintained down to such a short channel device is likely due to the use of the hetero-MIS structure, demonstrating the high-performance capability of ZnO-based FETs.

High-performance ZnO∕ZnMgO field-effect transistors using a hetero-metal-insulator-semiconductor structure

Characterization of a Zn0.7Mg0.3O∕ZnO heterostructure field-effect transistor (HFET) is reported. The HFET was based on a Zn0.7Mg0.3O∕ZnO∕Zn0.7Mg0.3O single quantum well (SQW) grown on an a-plane sapphire substrate by molecular-beam epitaxy, and was fabricated by a conventional photolithography technique combined with dry etching. Room-temperature characteristic of the HFET was a n-channel depletion type with a transconductance of 0.70mS∕mm and a field-effect mobility of 140cm2∕Vs, in good agreement with the electron Hall mobility in SQW of 130cm2∕Vs. The on∕off ratio at VDS=3V was ∼800, which was limited by an insufficiently suppressed leakage current through the bottom Zn0.7Mg0.3O barrier.

Characteristics of a Zn0.7Mg0.3O∕ZnO heterostructure field-effect transistor grown on sapphire substrate by molecular-beam epitaxy

ZnO and ZnMgO growth on a-plane sapphire by molecular beam epitaxy

This paper describes a strong piezoelectric carrier confinement at a ZnO/Zn0.6Mg0.4O heterointerface grown on an a-plane sapphire substrate by molecular beam epitaxy. A ZnO/Zn0.6Mg0.4O double-heterojunction structure was grown without intentional doping and the formation of a deep potential well for electrons was confirmed using cathodoluminescence and transmittance spectra. Photoluminescence spectra at 4.5 K consisted of an intense near-band-edge emission at 3.359 eV and a broad and weak peak on the low-energy side. The results of Hall effect measurement revealed that the conduction is n-type with a high carrier concentration of ?1.2?1013 cm-2. The mobilities are ?170 cm2/V?s at 300 K and ?400 cm2/V?s at 77 K without deterioration at lower temperatures; these values are much higher than those of a thick single-layer ZnO film grown on an a-plane sapphire substrate. We attribute these optical and electrical properties to the formation of two-dimensional electron gas at the ZnO/Zn0.6Mg0.4O heterointerface by the piezoelectric polarization in a strained ZnO well.

Masataka Inoue

Papers

Molecular beam epitaxial growth of wide bandgap ZnMgO alloy films on (111)-oriented si substrate toward UV-detector applications

High-performance ZnO∕ZnMgO field-effect transistors using a hetero-metal-insulator-semiconductor structure

Characteristics of a Zn0.7Mg0.3O∕ZnO heterostructure field-effect transistor grown on sapphire substrate by molecular-beam epitaxy

ZnO and ZnMgO growth on a-plane sapphire by molecular beam epitaxy

Piezoelectric Carrier Confinement by Lattice Mismatch at ZnO/Zn0.6Mg0.4O Heterointerface