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 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

https://chemistry.beloit.edu/classes/nanotech/ZnO/mattoday10_05_40.pdf

ZnO - nanostructures, defects, and devices

Leu-M

Transparent conductors as solar energy materials: A panoramic review

The sensitivity for detecting hydrogen with multiple ZnO nanorods is found to be greatly enhanced by sputter-depositing clusters of Pd on the surface. The resulting structures show a change in room- temperature resistance upon exposure to hydrogen concentrations in N2 of 10–500ppm of approximately a factor of 5 larger than without Pd. Pd-coated ZnO nanorods detected hydrogen down to 2.6% at 10ppm and >4.2% at 500ppm H2 in N2 after a 10min exposure. There was no response at room temperature to O2. Approximately 95% of the initial ZnO conductance after exposure to hydrogen was recovered within 20s by exposing the nanorods to either air or pure O2. This rapid and easy recoverability make the Pd-coated nanorods suitable for practical applications in hydrogen-selective sensing at ppm levels at room temperature with <0.4mW power consumption.

Hydrogen-selective sensing at room temperature with ZnO nanorods

A comparison is made of the sensitivities for detecting hydrogen with Pt-coated single ZnO nanorods and thin films of various thicknesses (20–350 nm). The Pt-coated single nanorods show a current response of approximately a factor of 3 larger at room temperature upon exposure to 500ppmH2 in N2 than the thin films of ZnO. The power consumption with both types of sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The optimum ZnO thin film thickness under our conditions was between 40–170 nm, with the hydrogen sensitivity falling off outside this range. The nanorod sensors show a slower recovery in air after hydrogen exposure than the thin films, but exhibit a faster response to hydrogen, consistent with the notion that the former adsorb relatively more hydrogen on their surface. Both ZnO thin and nanorods cannot detect oxygen.

Hydrogen sensing at room temperature with Pt-coated ZnO thin films and nanorods

Single ZnO nanowire metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated using nanowires grown by site selective molecular-beam epitaxy. When measured in the dark at 25°C, he depletion-mode transistors exhibit good saturation behavior, a threshold voltage of ∼−3V, and a maximum transconductance of order 0.3mS∕mm. Under ultraviolet (366nm) illumination, the drain–source current increase by approximately a factor of 5 and the maximum transconductance is ∼5mS∕mm. The channel mobility is estimated to be ∼3cm2∕Vs, which is comparable to that reported for thin film ZnO enhancement mode MOSFETs, and the on∕off ratio was ∼25 in the dark and ∼125 under UV illumination.

Depletion-mode ZnO nanowire field-effect transistor

The control of cell adhesion and viability by zinc oxide nanorods

Single ZnO nanorods with diameters of ∼130nm were grown on Au-coated Al2O3 substrates by catalyst-driven molecular beam epitaxy. Individual nanorods were removed from the substrate and placed between Ohmic contact pads and the current–voltage characteristics measured as a function of temperature and gas ambient. In the temperature range from 25to150°C, the resistivity of nanorods treated in H2 at 400°C prior to measurement showed an activation energy of 0.089±0.02eV and was insensitive to the ambient used (C2H4,N2O,O2 or 10% H2 in N2). By sharp contrast, the conductivity of nanorods not treated in H2 was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential as gas sensors.

B. S. Kang

Papers

Hydrogen-selective sensing at room temperature with ZnO nanorods

Hydrogen sensing at room temperature with Pt-coated ZnO thin films and nanorods

Depletion-mode ZnO nanowire field-effect transistor

The control of cell adhesion and viability by zinc oxide nanorods

Electrical transport properties of single ZnO nanorods