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Abstract: Pulsed Laser Deposition of high crystalline quality thin ZnO films on sapphire substrates necessitates a growth temperature of about 750 °C or higher while sharp interfaces in a multilayer structure suitable for optoelectronic devices are obtained at comparatively low growth temperatures. To meet these contradictory requirements a growth scheme has been evolved in which a ZnO buffer layer deposited at about 750 °C was found to facilitate high crystalline quality growth of a ZnO over layer even at 400 °C. The buffer layer grown at 750 °C was found to have its in plane lattice 30° rotated compared to that of the sapphire substrate and so was the case with the ZnO over layer grown at 400 °C on the buffer. The full width at half maximum of the high resolution X-ray diffraction rocking curves of (00.2) and (10.4) peaks of ZnO films grown at low temperature on the buffer were found to be ∼0.18° and ∼0.28°, respectively, which are comparable to 0.11° and 0.23° as observed in the case of films deposited directly at 750 °C and much better than the values of 0.46° and 0.48° seen in case of the films grown at 400 °C without any buffer layer. The buffer assisted low temperature ZnO growth also decreased the r.m.s. value of the surface roughness of the film to about 8 Å from about 40 Å of the one grown at high temperature without any buffer. [Copyright &y& Elsevier]

ZnO band-gap was engineered for and by growing its quantum wells and nanoparticle matrices using pulsed laser deposition. Alloy thin films of MgxZn1-xO grown with high crystalline quality by variable oxygen ambient pressure methodology developed by us could continuously increase the band gap up to about 3.8 eV. Increasing Cd concentration in the alloy thin films of CdyZn1-yO grown with good crystalline quality monotonically decreased the band gap up to about 2.9 eV. Multilayer matrices of alumina capped ZnO nanoparticles with mean radii in the range of 1.8–3.6 nm were grown to obtain size-dependent band gap up to about 4.5 eV. These nanoparticles are understood to grow without the formation of a wetting layer on the substrate. [Copyright &y& Elsevier]

The composition of nitrogen laser (wavelength 337 nm, pulse width 3 ns) induced ablation plumes from ZnSe and ZnO targets was studied at different laser fluences using a time-of-flight mass spectrometer. In the case of ZnSe, abundant ion signals corresponding to Se and ZnSe clusters, some of which were Se-rich, were detected with fluence-dependent distributions. At a laser fluence of 1250 J m[sup -2], clusters with elevated intensity were observed at sizes of 6, 13, 19, 23 and 33 ZnSe molecules (‘magic numbers’), which match quite well with the earlier observation by others of magic numbers of chemically similar ZnS produced by a conventional vaporization and quenching scheme. In the case of ZnO, we detected the presence of atomic Zn and molecular species of ZnO, as well as a series of (ZnO)[sub n]-type clusters with fluence-dependent distributions. Unlike the case of ZnSe, no magic numbers were observed for ZnO. [ABSTRACT FROM AUTHOR]

Abstract: Temperature dependence of the photoluminescence (PL) transitions in the range of 10–300K was studied for ZnO thin films grown on sapphire by pulsed laser deposition. The low temperature PL spectra were dominated by recombination of donor bound excitons (B X) and their phonon replicas. With increasing temperature, free exciton (F X) PL and the associated LO phonon replicas increased in intensity at the expense of their bound counterparts. The B X peak with line width of ∼6meV at 10K exhibited thermal activation energy of ∼17meV, consistent with the exciton-defect binding energy. The separation between the F X and B X peak positions was found to reduce with increasing temperature, which was attributed to the transformation of B X into the shallower donor bound exciton complexes at consecutive lower energy states with increasing temperature, which are possible in ZnO. The energy separation between F X peak and its corresponding 1-LO phonon replica showed stronger dependence on temperature than that of 2-LO phonon replica. However, their bound counterparts did not exhibit this behavior. The observed temperature dependence of the energy separation between the free exciton and it is LO phonon replicas are explained by considering the kinetic energy of free exciton. The observed PL transitions and their temperature dependence are consistent with observations made with bulk ZnO crystals implying high crystalline and optical quality of the grown films. [Copyright &y& Elsevier]

We have grown thin films of Dy doped ZnO (Dy:ZnO) on sapphire substrate using pulsed laser deposition with Dy concentration varying from 0.05 at.% to 1.8 at.%. These as grown Dy:ZnO thin films were characterized using low temperature four probe electrical measurements (in the range ~ 300 K to 4 K). All the Dy:ZnO thin films showed metal like behavior with a transition from positive to negative temperature coefficient of resistivity (TCR) and again to positive TCR with an increase of Dy concentration. This anomaly in conduction mechanism was investigated by considering quantum corrections to classical Boltzmann conductivity. All the Dy:ZnO thin films also exhibited negative magneto-resistance that supported for a significant contribution of weak localization in quantum corrections to conductivity. [ABSTRACT FROM AUTHOR]

Epitaxy of ZnO layers on cubic GaP(1 1 1) substrates has been demonstrated using pulsed laser deposition. Out of plane and in-plane epitaxial relationship of ZnO layer with respect to GaP substrate determined using phi ( ϕ ) scans in high resolution X-ray diffraction measurements are (0 0 0 1) ZnO ‖ (1 1 1) GaP and 〈 - 1 2 - 1 0 〉 ZnO ‖ - 1 1 0 GaP respectively. Our results of epitaxy of ZnO and its intense excitonic photoluminescence with very weak defect luminescence suggest that (1 1 1) oriented GaP can be a potential buffer layer choice for the integration of ZnO based optoelectronic devices on Si(1 1 1) substrates. [ABSTRACT FROM AUTHOR]

We have studied the band offset and alignment of pulsed laser deposited Al 2 O 3 /CuGaO 2 and ZnO/CuGaO 2 hetero-structures using photoelectron spectroscopy. Al 2 O 3 /CuGaO 2 interface exhibited a type I band alignment with valance band offset (VBO) of 4.05 eV whereas type II band alignment was observed in ZnO/CuGaO 2 hetero-structure with a VBO of 2.32 eV. Schematic band alignment diagram for the interface of these hetero-structures has been constructed. Band offset and alignment studies of these heterojunctions are important for gaining insight to the design of various optoelectronic devices based on such hetero-structures. [ABSTRACT FROM AUTHOR]

Abstract: This research article describes the large scale fabrication of ZnO nanorods of various shapes on Si(100) substrate, by using metalorganic precursor of Zn in solutions with microwave as the source of energy. This is a low temperature, environmental friendly and rapid thin film deposition process, where ZnO nanorods (1–3 μm length) were grown only in 1–5 min of microwave irradiation. All as-synthesized nanorods are of single crystalline grown along the <0001> crystallographic direction. The coated nanorods were found to be highly dense having a thickness of ∼1–3 μm over the entire area 20 mm × 20 mm of the substrate. The ZnO thin film comprising of nanorods exhibits good adhesion with the substrate. A possible mechanism for the initial nucleation and growth of ZnO is discussed. A cross over from a strong visible light emission to an enhanced UV emission is observed, when the nature of the surfactants are varied from polymeric to ionic and nonionic. The position of the chromaticity coordinates in yellow region of the color space gives an impression of white light generation from these coatings by exciting with a blue laser. [Copyright &y& Elsevier]

Intrinsic epitaxial zinc oxide (epi-ZnO) thin films were grown by laser-molecular beam epitaxy (L-MBE), i.e., pulsed laser deposition (PLD) technique using Johnson Matthey “specpure”-grade ZnO pellets. The effects of substrate temperatures on ZnO thin film growth, electrical conductivity (σ), mobility (μ) and carrier concentration (n) were studied. As well as the feasibility of developing high quality conducting oxide thin films was also studied simultaneously. The highest conductivity was found for optimized epi-ZnO thin films is σ=0.06×103 ohm-1 cm-1 (n-type) (which is almost at the edge of semiconductivity range), carrier density n=0.316×1019 cm-3 and mobility μ=98 cm2/V s. The electrical studies further confirmed the semiconductor characteristics of epi-n-ZnO thin films. The relationship between the optical and electrical properties were also graphically enumerated. The electrical parameter values for the films were calculated, graphically enumerated and tabulated. As a novelty point of view, we have concluded that without doping and annealing, we have obtained optimum electrical conductivity with high optical transparency (⩾95%) for as deposited ZnO thin films using PLD. Also, this is the first time that we have applied PLD made ZnO thin films to iso-, hetero-semiconductor–insulator–semiconductor (SIS) type solar cells as transparent conducting oxide (TCO) window layer. We hope that surely these data be helpful either as a scientific or technical basis in the semiconductor processing. [Copyright &y& Elsevier]

High quality epitaxial indium zinc oxide (heavily indium oxide doped) (epi-n-IZO) thin films were optimized by laser-molecular beam epitaxy (L-MBE) i.e., pulsed laser deposition (PLD) technique for fabricating novel iso- and hetero-semiconductor–insulator–semiconductor (SIS) type solar cells using Johnson Matthey “specpure”- grade 90% In2O3 mixed 10% ZnO (as commercial indium tin oxide (ITO) composition) pellets. The effects of substrate temperatures, substrates and heavy indium oxide incorporation on IZO thin film growth, opto-electronic properties with 〈1 0 0〉 silicon (Si), gallium arsenide (GaAs) and indium phosphide (InP) wafers were studied. As well as the feasibility of developing some novel models of iso- and hetero-SIS type solar cells using epi-IZO thin films as transparent conducting oxides (TCOs) and 〈1 0 0〉 oriented Si, GaAs and InP wafers as base substrates was also studied simultaneously. The optimized films were highly oriented, uniform, single crystalline approachment, nano-crystalline, anti-reflective (AR) and epitaxially lattice matched with 〈1 0 0〉 Si, GaAs and InP wafers without any buffer layers. The optical transmission T (max) ⩾ 95% is broader and absolute rivals that of other TCOs such as ITO. The highest conductivity observed is σ=0.47×103 Ω-1 cm-1 (n-type), carrier density n=0.168×1020 cm-3 and mobility μ=123 cm2/V s. From opto-electronic characterizations, the solar cell characteristics and feasibilities of fabricating respective epi-n-TCO/〈1 0 0〉 wafer SIS type solar cells were confirmed. Also, the essential parameters of these cells were calculated and tabulated. We hope that these data be helpful either as a scientific or technical basis in semiconductor processing. [Copyright &y& Elsevier]

We have optimised and deposited epitaxial indium zinc oxide (epi-IZO) (In2Zn2O5) thin films on 〈1 0 0〉 oriented Si, GaAs and InP by laser-molecular beam epitaxy (L-MBE) technique, i.e., pulsed laser deposition (PLD). Optimised growth conditions have been obtained for the deposition of high quality epi-IZO thin films. To our knowledge, this is the first time that the PLD deposited indium zinc oxide thin films on semiconductor wafers have been applied to semiconductor–insulator–semiconductor (SIS) iso- and hetero-type junction solar cell structures as wide band gap transparent conducting front electrode-window layers. We have carried out X-ray diffraction (XRD) and energy dispersive chemical analysis (EDAX) to determine the Structural and compositional properties of as-grown thin films. The crystalline quality of the obtained thin films is similar to that of the bulk single crystals. Increasing the deposition temperature leads the thin films to fine nano-structure nature. In the present work, the effects of various substrate temperatures, substrates and heavy indium oxide doping on indium zinc oxide thin film growth, structural and compositional properties were analysed. As well as our main aim, the feasibility of developing high quality transparent conducting oxide (TCO) thin films for opto-electronic devices was also studied simultaneously. Our novel achievement in this work is without any buffer layers, we have obtained good epitaxial lattice matching between the highly oriented IZO functional layers and the substrate materials suitable for III–V based high-speed opto-electronic and micro-electronic devices. [Copyright &y& Elsevier]

Highly textured zinc oxide (ZnO) thin films have been optimized and deposited by pulsed laser deposition (PLD), i.e., laser-molecular beam epitaxy technique on 〈100〉 Si, GaAs and InP wafers compatible with current semiconductor processing techniques. To our knowledge this is the first time that the PLD deposited zinc oxide thin films on semiconductor wafers have been applied to semiconductor–insulator–semiconductor type multi junction (homo and hetero) solar cell structures as wide band gap transparent conducting oxide (TCO) front electrode-emitter layers. In this present work, the effects of various substrate temperatures and substrates on ZnO thin film growth, structural and compositional properties were analyzed and the feasibility of developing high-quality TCO thin films for opto-electronic devices was also studied simultaneously. Increasing the deposition temperature leads the thin films to fine nano-structures. Our achievement in this work is elimination of any buffer layer like GaN and we have obtained good epitaxial lattice matching between the ZnO functional layers and the 〈100〉 substrates suitable for III–V-based high-speed opto- and micro-electronic devices. [Copyright &y& Elsevier]