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Abstract Electrodeposition is one of the leading non-vacuum techniques for the fabrication of CuInSe2 (CIS)-based solar cells. In the present work, pulse electrodeposition, an advanced technique, is utilized effectively for CIS absorber preparation devoid of any additives/complexing agents. An economic pulse electrodeposition is employed for the deposition of Cu/In stack followed by selenization to fabricate CIS absorbers on flexible and glass substrates. The approach uses a two-electrode system suitable for large area deposition and utilizes the fundamentals of pulse electrodeposition with appropriate optimization of parameters to obtain smooth Cu/In precursors. The selenized CIS absorbers are of 1 µm thick while possessing copper-poor composition (Cu/In ≈ 0.9) and tetragonal chalcopyrite phase. The fabricated devices have exhibited a power conversion efficiency of 5.2%. The technique can be further improved to obtain low-cost CIS solar cells which are suitable for various small-scale energy applications.

Highly transparent thin films of aluminium doped ZnO along with specific silver co-doping are deposited by sol-gel spin coating, which show preferred single orientation along (100) plane. Presence of Al dopant reduces, whereas co-doping with Ag improves crystallinity. Films show sharp absorption in near UV region and band gap observes minor shifts. UV and blue emission peaks are seen in the photoluminescence spectra. UV and blue emission peaks, respectively, demonstrate a fairly large i.e. 43% and 77% rise in the normalised intensity. Presence of Ag causes rise in UV peak because of enhanced excitonic recombination probability. Rise of blue emission intensity is ascribed to creation of Ag-Al interstitials. Surface roughness increases to 210.0 nm with Al increment into ZnO and drops drastically to 81.1 nm by Ag co-doping. Boundaries of nanostructures club together with rise in Al amount and thereafter Ag co-doping is seen to reduce the particle size. [ABSTRACT FROM AUTHOR]

For a detailed study on the semiconductor to metal transition (SMT) in ZnO thin films doped with Al in the concentration range from 0.02% to 2%, we grew these films on (0001) sapphire substrates using sequential pulsed laser deposition. It was found that the Al concentration in the films increased monotonically with the ratio of ablation durations of the alumina and ZnO targets used during the deposition. Using x-ray photo electron spectroscopy, it was found that while most of the Al atoms occupy the Zn sites in the ZnO lattice, a small fraction of the Al also gets into the grain boundaries present in the films. The observed SMT temperature decreased from ∼270 to ∼50 K with increase in the Al concentration from 0.02% to 0.25%. In the Al concentration range of ∼0.5% to 2%, these doped ZnO films showed metallic behavior at all the temperatures without undergoing any SMT. A theoretical model based on thermal activation of electrons and electron scatterings due to the grain boundaries, ionic impurities, and phonons has been developed to explain the observed concentration and temperature dependent SMT. [ABSTRACT FROM AUTHOR]

Pulsed laser deposition technique was used for growing thin films of ZnO on Si (100) substrate held at different temperatures (Ts). All the as-deposited films have shown a preferential c-axis orientation associated with varying grain size as a function of Ts ranging from 100 to 600 °C. Current-voltage (I-V) characteristics of these films show Ohmic behavior over the entire Ts range studied. These films were subjected to annealing at 800 °C in air ambient for 4 h. The grain size was observed to increase after the annealing process for all the films deposited at different Ts. Interestingly, these annealed films show nonlinear variation of current with applied voltage, very similar to the one observed in doped ZnO varistors. The nonlinear parameters such as the asymmetric behavior of change in current on the polarity reversal of voltage, the plateau region, and the break down voltage are observed to depend on Ts. This nonlinear behavior can perhaps be explained on the basis of electronic conduction model proposed for the bulk, doped ZnO varistors. The role of insulating intergranular layers between the disoriented microcrystallites is expected to be similar to that played by insulating intergranular layers in the doped ZnO varistors. [ABSTRACT FROM AUTHOR]

Electron transport layer (ETL) in perovskite-based solar cells (PSCs) is attractive from the perspective of photon-to-electron conversion efficiency. TiO2thin film is preferred in situations where microstructure, stability and charge transport characteristics are important. In this regard, we illustrate an approach that involves the synthesis of TiO2–pepsin thin film that can be used either as a mesoporous or compact layer depending on the device architecture of PSC devices. It was observed that pepsin acts as organic glue to TiO2nanoparticles and facilitates in controlling morphology of the thin film. The addition of pepsin did not have any adverse effect on TiO2anatase phase. Thickness and roughness of mesoporous and compact TiO2thin film suggested that controlled agglomeration can be achieved by tuning the concentration of pepsin in the precursor colloidal solution. The spin-coated thin films indicated high bulk mobility (205 cm2V−1 s−1) and good thermal stability over a wide range temperature (25–700°C). Furthermore, in the presence of pepsin group in TiO2thin film, the inherent optical properties were retained, as confirmed by UV–vis analysis. [ABSTRACT FROM AUTHOR]

Epitaxial thin films of (La0.5Pr0.2)Ba0.3MnO3 were deposited on LaAlO3 single-crystal substrates using pulsed laser deposition (PLD) technique with different growth parameters. Structural, surface morphological, electrical, and magnetotransport measurements on these films revealed that unoptimized growth parameters during the deposition using the third harmonic of a Q-switched Nd: YAG laser yielded structurally inhomogeneous epitaxial films having a columnar morphology, while the optimized growth parameters using an excimer laser during the PLD resulted in homogeneous epitaxial films with a smooth morphology. Interestingly, at a temperature of 5 K, the films with unoptimized growth parameters showed a large high-field magnetoresistance (MR) of ∼90% while the films with optimized growth parameters showed a high-field MR of only ∼15%. It is contemplated that this exceptionally large MR in the unoptimized films might be due to the phase separation and coexistence of metallic and insulating phases. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline Sr2FeMoO6 (SFMO) thin films were deposited at different substrate temperatures (500–800°C) on STO buffered Si (100) substrates by pulsed laser deposition (PLD). Structural analysis shows the single phase formation of polycrystalline SFMO thin films. A large (~12%) high field magnetoresistance (HFMR) was observed at 5K in polycrystalline films deposited at 800°C.. First time, we studied the MR effect in polycrystalline SFMO thin films grown on Si substrate, which make them very promising for magnetoresistive and spintronic applications and possibly open the future prospect for their possible integration in microelectronic industries. [Copyright &y& Elsevier]

Planar metal-insulator-metal (MIM) mono-dielectric layer stacks were fabricated using pulsed laser deposited thin films of high-k dielectric LaGdO3. These stacks showed high capacitance density ∼43.5 fF/μm2 with sub-nanometer capacitance equivalent thicknesses of ∼0.66 nm, large breakdown field of ∼6 MV/cm, greater energy storage density of ∼40 J/cm3, smaller voltage coefficient of capacitance, and lower dependence of it on layer thickness α ∝ d-1 and frequency. All these features make LaGdO3 a material of interest for next generation MIM structures for radio frequency, analog/mixed-signal, and dynamic random access memory applications. [ABSTRACT FROM AUTHOR]

Hafnium dioxide (HfO2) thin films with thicknesses ranging from 20 to 100 A have been grown in a viscous flow reactor using atomic layer deposition (ALD) with tetrakis(dimethylamido)hafnium(IV) and water as the reactants. HfO2 ALD films are deposited successfully at 200°C on different molecular monolayers. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy analyses show a continuous growth of the Hf02 layer on the self-assembled monolayer molecules. Electrical properties characterized by current-voltage measurements suggest that three parameters play important roles in determining the physical structure of HfO2, namely, the precursor pulse time, the sample exposure time, and the time for purging Out an unreacted precursor. ALD conditions for different substrates have been optimized so that excellent electrical properties can be obtained for HfO2 films on molecules. Transmission electron microscopy of 30 and 60 A ALD HfO2 on TiN and molecular monolaycrs shows a continuous deposition of HfO2. This process enables the development of a class of molecular electronic devices, solid-state molecular memory devices. [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]

It is believed that this is the first time that laser molecular beam epitaxy, i. e. pulsed laser deposition (PLD), deposited epitaxial indium zinc oxide (epi-IZO) thin films on float glass, <100> Si, GaAs and InP wafers have been applied to semiconductor–insulator–semiconductor type heterojunction solar cell structures as wide band gap transparent conducting oxides front electrode collector layers. In the present work, the effects of substrate temperatures, substrates and heavy indium oxide incorporation on epi-IZO thin film growth and novel surface morphological properties were analyses. Hitachi SEM and nanoscope atomic force microscopy revealed that the films were high quality nanostructures, which vary with different substrate temperatures and type of substrate. The morphological study is significant as reported so far. Increasing the substrate temperature causes the films to form a fine nanostructure. Better surface quality was observed on InP than Si and GaAs. Therefore, by the use of PLD with different substrate temperatures and substrates as control tools, a novel nano-architecture was developed for IZO thin films on glass, Si, GaAs and InP semiconductor single crystal wafers. Heavy indium oxide incorporation improves the surface quality of the thin films. The present work will be used, and these data may be helpful, as a scientific or technical basis in semiconductor processing and technology, such as nano-electronics (invisible security circuits) and nanomachining technology. SE/S280 [ABSTRACT FROM AUTHOR]

We investigated the effects of post-growth annealing in the temperature range of 873 to 1273 K on the spectral features of photoluminescence (PL) vis-à-vis the crystalline and compositional native defects of ZnO thin films grown at 773 K by pulsed laser deposition (PLD) on sapphire substrates. It is found in the PL spectra at 10 K that the deep level emission (DLE) shifted from red-orange spectral region of ∼1.8-2.4 eV to yellow-green region of ∼2.4-2.9 eV with the increasing temperature of annealing. We propose that the PL in red-orange region originating from the singly ionized oxygen vacancies diminished due to increased replenishment of oxygen with increasing annealing temperature and that in the yellow-green region originating from the oxygen interstitials and/or zinc vacancies increased due to enhanced concentration of these point defects. As the annealing temperature was increased, the overall intensity of PL in the DLE region increased slightly up to 973 K but beyond that it increased steeply and made a quantum leap at 1073 K. In contrast to that, intensity of PL due to the near band-edge emission (NBE) in UV region of ∼3.15 to 3.45 eV increased very steeply up to the annealing temperature of 973 K, which is found to be due to improvement in the crystalline and compositional qualities of the films and beyond that it dropped drastically due to deteriorations of these qualities. The high resolution PL spectra at 10 K in the NBE region mainly consisted of peaks due to the recombinations of neutral donor bound excitons' complexes (D0X) at ∼3.36 eV, free excitons (FXA) at ∼3.38 eV with their conspicuous LO phonon replicas and some other features such as exciton complexes bound to surface states or transitions of conduction band electrons to acceptor levels located in stacking faults and recombination of neutral acceptor bound excitons. The relative intensities of these individual features were strongly dependent on the annealing temperature of the films and the ensuing crystalline and compositional qualities. The 10 K PL spectra from the interfacial region of the annealed ZnO films and the sapphire substrates observed from the backside of the samples showed that the annealing temperature affected the crystalline and compositional qualities at the interface in a complex manner. Particularly, the features corresponding to the interface deteriorations resulting from the diffusion of Al into the ZnO films and the crystalline defects at the interface caused by the sputtering due to the PLD plume were prominently present in these PL spectra. These studies provide deeper insight into the fundamental PL processes in ZnO thin films annealed at different temperatures. [ABSTRACT FROM AUTHOR]

Studies on band-offset and band-alignment of heterojunction of highly c-axis oriented ZnO thin films grown on n-Ge (1 1 1) by pulsed laser deposition show a type-II band alignment with the valence band offset (ΔEV) of 3.1 ± 0.2 eV. The valence band spectra of this heterojunction show band onsets corresponding to Ge, interfacial GeOx, and ZnO layers. This observation also enabled us to determine ΔEV of ZnO/GeOx heterojunction to be 1.4 ± 0.2 eV. These studies provide further insight into the band alignment of ZnO/GeOx/Ge system wherein the observed large value of ΔEV of ZnO/Ge can be used for heterojunction based optoelectronic devices. [ABSTRACT FROM AUTHOR]

In order to achieve ultrafast response in MgZnO based self-powered Schottky type photodetectors, it is crucial to decrease both the junction capacitance and carrier transit time. To meet these criteria, Au/MgZnO/ITO Schottky junction photodetectors have been realised in crossbar pattern, wherein the thickness of the MgZnO thin film deposited on patterned ITO-glass substrate is ∼ 200 nm and the cross-sectional area of the devices is 0.032 mm2. The semi-transparent 10 nm Au electrode on top of the MgZnO film serves as the Schottky electrode through which light enters the devices. The vertical geometry of the crossbar pattern and the associated small device cross-section results in a low junction capacitance of the devices of ∼ 27 pF at zero bias, which in turn produces very fast visible blind self-powered ultraviolet (UV) photoresponse with both the rise and fall times of ∼ 1.5 μs, that is hitherto unreported for MgZnO based Schottky junction photodetectors. The devices also demonstrate a peak responsivity of ∼ 49 mA/W at ∼ 280 nm with a cut-off wavelength of 336 nm. These Au/MgZnO/ITO Schottky photodetectors in crossbar pattern, with optimized device area, could be useful in applications requiring fast response, such as UV communication and UV imaging. [Display omitted] • Self-powered Au/MgZnO/ITO vertical Schottky junction photodetectors have been realized in crossbar geometry. • The junctions show visible blind UV photoresponse with rise and decay times of 1.5 μs. • The responsivity of self-powered Au/MgZnO/ITO devices at zero bias is about 49 mA/W. • By utilizing crossbar geometry, the junction capacitance could be reduced to ∼ 27 pF. [ABSTRACT FROM AUTHOR]

Lattice parameter of NiO layers deposited using pulsed laser deposition is determined accurately using three parallel Bragg reflections. A small decrease in out of plane lattice parameter is found as O 2 partial pressure is increased, which is attributed to the lattice contraction due to Ni vacancies. The NiO layers are found to be oriented along (111) direction on (0001) oriented Al 2 O 3 substrate. The presence of Pendellosung oscillations indicates high crystalline and interfacial qualities of NiO layers, which gradually degrade with increase in O 2 partial pressure. The NiO layer thickness determined from both x-ray diffraction and x-ray reflectivity show similar trend with O 2 partial pressure. The optical band gap does not vary much due to the presence of very small compressive strain. [ABSTRACT FROM AUTHOR]

Abstract: Photoluminescence (PL) of high quality GaN epitaxial layer grown on β-Si3N4/Si (111) substrate using nitridation–annealing–nitridation method by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated in the range of 5–300K. Crystallinity of GaN epilayers was evaluated by high resolution X-ray diffraction (HRXRD) and surface morphology by Atomic Force Microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). The temperature-dependent photoluminescence spectra showed an anomalous behaviour with an ‘S-like’ shape of free exciton (FX) emission peaks. Distant shallow donor–acceptor pair (DAP) line peak at approximately 3.285eV was also observed at 5K, followed by LO replica sidebands separated by 91meV. The activation energy of the free exciton for GaN epilayers was also evaluated to be ∼27.8±0.7meV from the temperature-dependent PL studies. Low carrier concentrations were observed ∼4.5±2×1017 cm−3 by measurements and it indicates the silicon nitride layer, which not only acts as a growth buffer layer, but also effectively prevents Si diffusion from the substrate to GaN epilayers. The absence of yellow band emission at around 2.2eV signifies the high quality of film. The tensile stress in GaN film calculated by the thermal stress model agrees very well with that derived from Raman spectroscopy. [Copyright &y& Elsevier]

Abstract: Non-polar a-plane GaN films were grown on an r-plane sapphire substrate by plasma assisted molecular beam epitaxy (PAMBE). The effect of growth temperature on structural, morphological and optical properties has been studied. The growth of non-polar a-plane (11−20) orientation of the GaN epilayers were confirmed by high resolution X-ray diffraction (HRXRD) study. The X-ray rocking curve (XRC) full width at half maximum of the (11−20) reflection shows in-plane anisotropic behavior and found to decrease with increase in growth temperature. The atomic force micrograph (AFM) shows island-like growth for the film grown at a lower temperature. Surface roughness has been decreased with increase in growth temperature. Room temperature photoluminescence shows near band edge emission at 3.434–3.442eV. The film grown at 800°C shows emission at 2.2eV, which is attributed to yellow luminescence along with near band edge emission. [ABSTRACT FROM AUTHOR]

Abstract: Transparent conductive dysprosium doped ZnO (Dy:ZnO) thin films with preferential orientation in the (0002) direction were deposited on (0001) sapphire substrate by buffer assisted pulsed laser deposition. The experimental results show that the resistivity of Dy:ZnO thin films decreased to a minimum value of ∼7.6×10−4 Ωcm with increasing Dy concentration up to ∼0.45at%, then increased with the further increase of Dy concentration. On the contrary, the band gap and carrier concentration of Dy:ZnO thin films initially increased, then decreased with increase of Dy concentration. The blue shift of band gap of Dy:ZnO thin films with increasing carrier concentration was attributed to the competing effects of Burstein-Moss shift and band gap narrowing. A bright room temperature photoluminescence observed at ∼575nm in all the Dy:ZnO thin films, with maximum intensity at ∼0.45at% of Dy doping, was attributed to be due to intra-band transitions of Dy3+ in ZnO. Near band edge photoluminescence of ZnO was observed at ∼380nm with photoluminescence intensity decreasing with increase of Dy concentration. Such Dy:ZnO thin films are found to be suitable candidate for luminescent device applications. [Copyright &y& Elsevier]

We have observed weak localization induced by disorder in thin films of Gd doped ZnO (Gd:ZnO) deposited by pulsed laser deposition (PLD). Disorder parameter (K f l) of all the Gd:ZnO thin films was found to be greater than 1, which indicates that thin films of Gd:ZnO in this study are in metallic side of metal-insulator transition. However, temperature dependent resistivity studies of all the Gd:ZnO thin films exhibits negative temperature coefficient of resistance (TCR) showing semiconductor like nature at low temperatures. This anomaly in temperature dependent resistivity behaviour has been attributed to the dominant presence of weak localization. Magnetoresistance measurements confirms the dominant influence of weak localization in the conducting mechanism of Gd:ZnO films. Phase coherent length was found to be varied with the concentration of Gd and reports the highest value at ~360 nm for Gd:ZnO thin film with 1 at.% of Gd concentration.. • Disorder induced weak localization was observed in thin films of Gd doped ZnO deposited by pulsed laser deposition. • The observation of negative magnetoresistance confirms the dominant role of weak localization in the Gd doped ZnO films. • Phase coherent length was found to be varied with the concentration of Gd and reports the highest value at ~ 360 nm. • Electron electron interaction acts as a dominant phase breaking mechanism of weak localization in Gd:ZnO thin films. [ABSTRACT FROM AUTHOR]

Abstract: Transparent diode heterojunction on ITO coated glass substrates was fabricated using p-type AgCoO2 and n-type ZnO films by pulsed laser deposition (PLD). The PLD of AgCoO2 thin films was carried out using the pelletized sintered target of AgCoO2 powder, which was synthesized in-house by the hydrothermal process. The band gap of these thin films was found to be ∼3.89 eV and they had transmission of ∼55% in the visible spectral region. Although Hall measurements could only indicate mixed carrier type conduction but thermoelectric power measurements of Seebeck coefficient confirmed the p-type conductivity of the grown AgCoO2 films. The PLD grown ZnO films showed a band gap of ∼3.28 eV, an average optical transmission of ∼85% and n-type carrier density of ∼4.6×1019 cm− 3. The junction between p-AgCoO2 and n-ZnO was found to be rectifying. The ratio of forward current to the reverse current was about 7 at 1.5 V. The diode ideality factor was much greater than 2. [Copyright &y& Elsevier]