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

Physical Review B

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

Optical properties of ZnO nanostructures.

Progress in preparation, processing and applications of polyaniline

Recent progress in processing and properties of ZnO

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation.

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Electrical Characterization of 1.8 MeV Proton-Bombarded ZnO

Gold Schottky-barrier diodes (SBDs) were fabricated on vapor-phase-grown single-crystal ZnO. Deep-level transient spectroscopy, using these SBDs, revealed the presence of four electron traps, the major two having levels at 0.12 eV and 0.57 below the conduction band. Comparison with temperature-dependent Hall measurements suggests that the 0.12 eV level has a temperature activated capture cross section with a capture barrier of about 0.06 eV and that it may significantly contribute to the free-carrier density. Based on the concentrations of defects other than this shallow donor, we conclude that the quality of the vapor-phase-grown ZnO studied here supercedes that of other single-crystal ZnO reported up to now.

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Electrical Characterization of Vapor-Phase-Grown Single-Crystal ZnO

Epitaxial n-GaN was irradiated with 5.4-MeV He ions. Capacitance–voltage (C–V) measurements showed that 5.4-MeV He ions remove free carriers at a rate of 6200±300 cm−1 in the first micron below the surface. Deep level transient spectroscopy (DLTS) revealed that, in addition to the radiation-induced defects previously detected by DLTS at 0.18–0.20 eV below the conduction band, He-ion irradiation introduced two additional prominent defects, ER4 (EC-0.78 eV) and ER5 (EC-0.95 eV) at rates of 1510±300 and 3030±500 cm−1, respectively. Capture cross-section measurements revealed that electron capture kinetics of ER5 is similar to that of a line defect.

Electrical characterization of two deep electron traps introduced in epitaxially grown n-GaN during He-ion irradiation

Using deep-level transient spectroscopy, we have studied the electrical properties of defects introduced in epitaxially grown n-GaN during 2-MeV proton bombardment. The main defects detected, ER2 and ER3, are introduced at rates of 400±150 and 600±100 cm−1, respectively, and have energy levels at 0.16±0.03 and 0.20±0.01 eV, respectively, below the conduction band. A less prominent defect, ER1, with an energy level at 0.13±0.01 eV below the conduction band, is introduced at a rate of 30±10 cm−1. The small capture cross section of ER3 [(8±4)×10−18 cm2] implies that it is in a neutral or negative state when above the Fermi level.

Proton bombardment-induced electron traps in epitaxially grown n-GaN

Temperature dependent current–voltage ( I – V ) and Hall measurements were performed on Pd/ZnO Schottky barrier diodes in the range 20–300 K The apparent Richardson constant was found to be 860 × 10 - 9 A K - 2 cm - 2 in the 60–160 K temperature range, and mean barrier height of 050 eV in the 180–300 K temperature range After barrier height inhomogeneities correction, the Richardson constant and the mean barrier height were obtained as 167 A K - 2 cm - 2 and 061 eV in the temperature range 80–180 K, respectively A defect level with energy at 012 eV below the conduction band was observed using the saturation current plot and ( 011 ± 001 ) eV using deep level transient spectroscopy measurements

F.D. Auret

Papers

Electrical Characterization of 1.8 MeV Proton-Bombarded ZnO

Electrical Characterization of Vapor-Phase-Grown Single-Crystal ZnO

Electrical characterization of two deep electron traps introduced in epitaxially grown n-GaN during He-ion irradiation

Proton bombardment-induced electron traps in epitaxially grown n-GaN

Analysis of temperature dependent I―V measurements on Pd/ZnO Schottky barrier diodes and the determination of the Richardson constant