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 Raman scattering study of wurtzite $\mathrm{ZnO}$ over a temperature range from 80 to $750\phantom{\rule{03em}{0ex}}\mathrm{K}$ Second-order Raman features are interpreted in the light of recent ab initio phonon density of states calculations The temperature dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously Some weak, sharp Raman peaks are detected whose temperature dependence suggests they may be due to impurity modes High-resolution spectra of the ${E}_{2}^{\mathrm{high}}$, ${A}_{1}(\mathrm{LO})$, and ${E}_{1}(\mathrm{LO})$ modes were recorded, and an analysis of the anharmonicity and lifetimes of these phonons is carried out The ${E}_{2}^{\mathrm{high}}$ mode displays a visibly asymmetric line shape This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the $K$ point, where the two-phonon density of states displays a sharp edge around the ${E}_{2}^{\mathrm{high}}$ frequency The temperature dependence of the linewidth and frequency of the ${E}_{2}^{\mathrm{high}}$ mode is well described by a perturbation-theory renormalization of the harmonic ${E}_{2}^{\mathrm{high}}$ frequency resulting from the interaction with the acoustic two-phonon density of states In contrast, the ${A}_{1}(\mathrm{LO})$ and ${E}_{1}(\mathrm{LO})$ frequencies lie in a region of nearly flat two-phonon density of states, and they exhibit a nearly symmetric Lorentzian line shape with a temperature dependence that is well accounted for by a dominating asymmetric decay channel

Temperature dependence of Raman scattering in ZnO

The present invention relates to a process of making a zinc-oxide-based thin film semiconductor, for use in a transistor, comprising thin film deposition onto a substrate comprising providing a plurality of gaseous materials comprising at least first, second, and third gaseous materials, wherein the first gaseous material is a zinc-containing volatile material and the second gaseous material is reactive therewith such that when one of the first or second gaseous materials are on the surface of the substrate the other of the first or second gaseous materials will react to deposit a layer of material on the substrate and wherein the third gaseous material is inert with respect to reacting with the first or second gaseous materials.

Process for atomic layer deposition

The III-nitrides include the semiconductors AlN, GaN and InN, which have band gaps spanning the entire UV and visible ranges. Thin films of III-nitrides are used to make UV, violet, blue and green light-emitting diodes and lasers, as well as solar cells, high-electron mobility transistors (HEMTs) and other devices. However, the film growth process gives rise to unusually high strain and high defect densities, which can affect the device performance. X-ray diffraction is a popular, non-destructive technique used to characterize films and device structures, allowing improvements in device efficiencies to be made. It provides information on crystalline lattice parameters (from which strain and composition are determined), misorientation (from which defect types and densities may be deduced), crystallite size and microstrain, wafer bowing, residual stress, alloy ordering, phase separation (if present) along with film thicknesses and superlattice (quantum well) thicknesses, compositions and non-uniformities. These topics are reviewed, along with the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides. A summary of useful values needed in calculations, including elastic constants and lattice parameters, is also given. Such topics are also likely to be relevant to other highly lattice-mismatched wurtzite-structure materials such as heteroepitaxial ZnO and ZnSe.

https://iopscience.iop.org/article/10.1088/0034-4885/72/3/036502/pdf

X-ray diffraction of III-nitrides

Several hundred thousands of tons of ZnO are used by per year, e.g. as an additive to concrete or to rubber. In the field of optoelectronics, ZnO holds promises as a material for a blue/UV optoelectronics, alternatively to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits, which are transparent in the visible or for semiconductor spintronics. The main problem is presently, however, a high, reproducible and stable p-doping. We review in this contribution partly critically the material growth, fundamental properties of ZnO and of ZnO-based nanostructures, doping as well as present and future applications, with emphasis on the electronic and optical properties including stimulated emission. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO : From basics towards applications

Polarized micro-Raman measurements were performed to study the phonon modes of Fe, Sb, Al, Ga, and Li doped ZnO thin films, grown by pulsed-laser deposition on c-plane sapphire substrates. Additional modes at about 277, 511, 583, and 644 cm−1, recently assigned to N incorporation [A. Kaschner et al., Appl. Phys. Lett. 80, 1909 (2002)], were observed for Fe, Sb, and Al doped films, intentionally grown without N. The mode at 277 cm−1 occurs also for Ga doped films. These modes thus cannot be related directly to N incorporation. Instead, we suggest host lattice defects as their origin. Further additional modes at 531, 631, and 720 cm−1 seem specific for the Sb, Ga, and Fe dopants, respectively. Li doped ZnO did not reveal additional modes.

Raman scattering in ZnO thin films doped with Fe, Sb, Al, Ga, and Li

Infrared dielectric function spectra and phonon modes of high-quality, single crystalline, and highly resistive wurtzite ZnO films were obtained from infrared (300–1200 cm−1) spectroscopic ellipsometry and Raman scattering studies. The ZnO films were deposited by pulsed-laser deposition on c-plane sapphire substrates and investigated by high-resolution x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering experiments. The crystal structure, phonon modes, and dielectric functions are compared to those obtained from a single-crystal ZnO bulk sample. The film ZnO phonon mode frequencies are highly consistent with those of the bulk material. A small redshift of the longitudinal optical phonon mode frequencies of the ZnO films with respect to the bulk material is observed. This is tentatively assigned to the existence of vacancy point defects within the films. Accurate long-wavelength dielectric constant limits of ZnO are obtained from the infrared ellipsometry anal...

Infrared dielectric functions and phonon modes of high-quality ZnO films

Infrared dielectric function spectra and phonon modes with polarization parallel and perpendicular to the c axis of high quality, highly relaxed, and single crystalline wurtzite MgxZn1−xO films with 0⩽x⩽0.2 prepared by pulsed-laser deposition on c-plane sapphire substrates were obtained from infrared spectroscopic ellipsometry (380–1200 cm−1) and Raman scattering studies. A two-mode behavior is found for the modes with E1 symmetry, a lattice mode and an impurity-type mode are obtained for the A1 symmetry phonons. Model dielectric function spectra will become useful for future infrared ellipsometry analysis of complex MgxZn1−xO-based heterostructures.

Infrared dielectric functions and phonon modes of wurtzite MgxZn1−xO (x⩽0.2)

Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition on (0001) sapphire are reported. The wurtzite-structure ZnO layers serve as transparent conducting electrodes. Previously observed coupling effects within the wurtzite-perovskite heterostructure by spectroscopic electro-optic ellipsometry birefringence measurements manifest themselves as a “pinning” of the ferroelectric polarization in the BaTiO3 layer by the cladding ZnO layers. Temperature-controlled electro-optic Raman measurements assign the electro-optic birefringence results to a temperature-driven phase transition resulting from the leakage current within the sample. High-temperature small-signal capacitance measurements exploiting the conductive electrode properties of the cladding layers reveal occurrence of the Curie temperature of the BaTiO3 layer at 384 K.

Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition

We report on temperature, time, and voltage dependent resistive hysteresis measurements of BaTiO3-ZnO heterostructures grown on (001) Si substrates by pulsed laser deposition We observe a diodelike behavior and cycling-voltage dependent hysteresis formation under forward bias We explain these effects with depletion layer formation between the ZnO and BaTiO3 layers, an additional barrier due to the spontaneous polarization of ZnO and the ferroelectric nature of BaTiO3 The disappearance of the resistive hysteresis above the ferroelectric-paraelectric phase transition temperature of BaTiO3 conformed that the hysteresis is related to the ferroelectricity of BaTiO3 Time dependent resistance measurements reveal memory effects

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N. Ashkenov

Papers

Raman scattering in ZnO thin films doped with Fe, Sb, Al, Ga, and Li

Infrared dielectric functions and phonon modes of high-quality ZnO films

Infrared dielectric functions and phonon modes of wurtzite MgxZn1−xO (x⩽0.2)

Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition

Resistive hysteresis and interface charge coupling in BaTiO3-ZnO heterostructures