Search

Amorphous YCrO3 (YCO) films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition in order to investigate resistive switching (RS) phenomenon. The Pt/YCO/Pt device showed stable unipolar RS with resistance ratio of ∼105 between low and high resistance states, excellent endurance and retention characteristics, as well as, non-overlapping switching voltages with narrow dispersions. Based on the x-ray photoelectron spectroscopy and temperature dependent switching characteristics, observed RS was mainly ascribed to the oxygen vacancies. Moreover, current-voltage characteristics of the device in low and high resistance states were described by Ohmic and trap controlled space-charge limited conduction mechanisms, respectively. [ABSTRACT FROM AUTHOR]

We report the crystal structure, dielectric, transport, and magnetic properties of Ni0.65Zn0.35Fe2O4. Rietveld refinement results of X-ray diffraction patterns confirm the phase formation of the material with cubic crystal structure (Fd3m). The frequency dependent ac conductivity behavior obeys the Jonscher's power law and is explained using the jump relaxation model. The observed behavior of temperature dependent bulk conductivity is attributed to the variable-range hopping of localized polarons. The correlation of polaron conduction and high permittivity behavior of NZFO is established on the basis of long range and short range conduction mechanisms. The complex impedance spectra clearly show the contribution of both grain and grain boundary effect on the electrical properties. [ABSTRACT FROM AUTHOR]

Forming free and thermally stable bipolar resistive switching behavior was observed in the memory devices composed of graphene oxide (GO) thin films on ITO coated glass substrate with Platinum (Pt) as the top electrode. The switching between the low resistance state and high resistance state showed a reliable and repeating behavior with an on/off ratio of 104 at room temperature. The Pt/GO/ITO device showed metallic and semiconducting characteristics in low and high resistance states, respectively, when resistance was measured as a function of temperature. Ohmic conduction was found to dominate in all regions of switching operation except for the high voltage regime of high resistance state where space charge limited conduction was found to be the main mechanism of current conduction. The device showed good endurance up to 104 s and retention characteristics up to 100 cycles with on/off ratio ∼104. The switching mechanism was found to be governed by migration of oxygen between GO layer and bottom ITO electrode, which was further confirmed by Raman Spectroscopy. The device exhibited stable bipolar switching characteristics with good retention and endurance properties at high temperatures up to 500 K. The graphene oxide based memory devices fabricated by simple chemical method have potential in the field of nonvolatile memory applications well above the room temperature. [ABSTRACT FROM AUTHOR]

A self-powered UV sensor with high responsivity was developed by coupling ZnO based piezoelectric nanogenerator and photodetector for uninterrupted real-time monitoring of UV radiation. Unlike conventional UV photodetectors, our approach couples a ZnO based metal-semiconductor-metal photodetector as a variable load resistor with a flexible ZnO:PVDF piezoelectric nanogenerator through impedance matching to realize self-powering of photodetector. The as fabricated UV photodetector exhibits a dark resistance of approximately 55 MΩ and change of resistance from 12 to 2 MΩ in response to UV illumination ranging from 1.5 to 14.5 mW/cm2. Under UV exposure of 1.5 mW/cm2, the output voltage of self-powered UV sensor drops from ∼14.6 V (dark) to ∼3.88 V. With increasing UV intensity from 1.5 to 14.5 mW/cm2, the output voltage gradually decreases from ∼3.88 to ∼1.04 V due to reduced ZnO photodetector resistance. This self-powered UV sensor exhibits excellent performance with a sensitivity of ∼93%, a voltage responsivity of 7.14 V (mW−1 cm−2), a response time of 0.67 s, and a recovery time of 4 s, which are better than the previous reports. The environmentally stable and biocompatible nature of ZnO based system makes it a promising candidate for self-powered real time ultraviolet remote sensing applications. [ABSTRACT FROM AUTHOR]

Abstract: In a recent report, Lee et al. have proposed an “effective field model” for extrinsic doping to explain the electrical properties of Al‐doped zinc oxide (ZnO) films grown by atomic layer deposition (ALD). They have introduced the doping model by considering the layered structure of the ALD‐grown films as observed in the transmission electron microscopy measurements. However, in the present comment, we have demonstrated that the suggested doping model is misleading in which physically inconsistent assumptions are considered throughout. Herein, a reasonable interpretation of the electrical properties and doping mechanism of the ALD‐grown films by taking into consideration the theoretical formulations of the disordered electronic system is suggested. [ABSTRACT FROM AUTHOR]

High quality (1 0 0) oriented thin films of (Y 0.9 Bi 0.1 )(Fe 0.5 Cr 0.5 )O 3 [YBFCO] were deposited on (1 0 0) LAO substrates with conducting LNO buffer layer as bottom electrode. YBFCO thin film was found to demonstrate interesting room temperature multiferroic properties where the origin of weak ferroelectricity could be mainly attributed to disordered transition metal ions of unlike spins, and magnetic behavior was ascribed to uncompensated weak ferromagnetism arises due to magnetic cluster state in disordered system. Dielectric anomaly near magnetization reversal temperature ( T irr ) revealed magnetodielectric effect in YBFCO film. In addition, leakage current behavior of the film was explained by trap-controlled space-charge-limited current conduction (SCLC) mechanism. [ABSTRACT FROM AUTHOR]

We report the switchable photovoltaic effects in graphene/BiFeO3/Pt heterostructures. Pure phase polycrystalline BiFeO3 films were deposited on Pt/TiO2/SiO2/Si substrates by pulse laser deposition. A bilayer graphene was transferred onto the BiFeO3 film which serves as transparent conducting electrodes. The heterostructures showed switchable photovoltaic effect depending on ferroelectric polarization directions indicating depolarization field induced separation of photogenerated carriers. The open circuit voltage (VOC) and short circuit current density (JSC) were measured to be ~ 110 mV, ~92 μA/cm² in positive polarity and similar values were obtained when the polarity was reversed. The JSC and VOC also showed rapid response (< 100 ms) as a function of light exposure time. [ABSTRACT FROM AUTHOR]

Highlights: [•] High quality thin film of multiferroic BiFeO3 on SrRuO3 is grown by RF Sputtering. [•] The Pt/BFO/SRO structure showed diode like behavior through I–V measurement. [•] Appreciable VOC and JSC were observed with illumination of white light. [•] The photoresponse at zero bias of BFO film showed rapid increase in photocurrent. [•] Application of BFO film for photosensitive capacitor is demonstrated. [ABSTRACT FROM AUTHOR]

We report enhancement of photovoltaic properties of highly oriented BiFeO3(BFO) thin films. The single phase rhombohedral R3c space group structure was confirmed by XRD and Raman spectra in the films grown on SrTiO3(111) substrates using RF magnetron sputtering. The films of BFO were characterized in planar geometry with top Pt electrodes having 200μm diameter, ∼40nm thickness and at a regular spacing of ∼150μm deposited by DC sputtering process. For photovoltaic studies the current voltage characteristic of as grown and poled samples were studied under the white light illumination having energy density of ∼1kW/m2. The as grown films showed open circuit voltage (Voc) of ∼3.9V which increased up to ∼17.8V on poling with 200V. This enhancement in Voc by poling was attributed to increase in net polarization due to alignment of domains in the direction of applied electric field and hence potential barriers between the domains. [ABSTRACT FROM AUTHOR]

The unipolar resistive switching characteristics of the amorphous LaLuO3thin films deposited by pulsed laser deposition have been studied. Reliable and repeatable nonvolatile switching of the resistance of LaLuO3films was obtained between two well defined states of low and high resistance with nearly constant resistance ratio ∼107and non-overlapping switching voltages in the range of 0.66-0.83 V and 1.9-2.7 V respectively. The temperature dependent measurement revealed metallic and semiconducting behavior in low and high resistance states respectively. The switching between low and high resistance states was attributed to the change in the separation between oxygen vacancies in light of the correlated barrier hopping theory. The current conduction mechanism of the device in high-resistance state followed the Poole's law, whereas the conduction in low-resistance state was found to be dominated by percolation. The resistance of low and high resistance states of the film showed no obvious degradation for up to ∼104seconds indicating good retention. The achieved characteristics of the resistive switching in LaLuO3thin films seem to be promising for futuristic nonvolatile memory applications. [ABSTRACT FROM AUTHOR]

Abstract: A novel multilevel resistive switching was observed in trilayer stacked geometry composed of graphene nano flakes sandwiched between polyvinylidene fluoride layers fabricated by spin coating method, which are expected to fulfill the need of high density data storage memories. External parameters such as current compliance and induced voltage pulse imposed on the devices provided an aid to tune the inherent resistance states. As fabricated devices exhibited multi level switching with stable resistance ratios between different resistance states having excellent data retention and endurance. Space charge limited conduction and Fowler–Nordheim (F–N) tunneling were found to be responsible for the switching mechanism. Graphene enriched with trapping sites provides the adequate environment for F–N tunneling process to occur, resulting in multi-bit resistance states. [Copyright &y& Elsevier]

Multilevel resistive switching was observed in random access memory device using amorphous SmGdO3 (SGO) ternary oxide thin films. Non-volatile and stable 4-level resistance states with sufficient margin of resistance ratios were observed by varying compliance current which was attributed to compliance current dependent variation in size of conducting filaments. As fabricated Pt/SGO/Pt devices exhibited excellent switching parameters such as stable resistance ratios of reset (ON) to set (OFF) states, non-overlapping switching voltages, excellent data retention, and endurance. Temperature dependent variation of resistances of ON and OFF states of the device was studied to elucidate current conduction and resistive switching mechanisms. [ABSTRACT FROM AUTHOR]

Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm2 and 9.3 mA/cm2 has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87 and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×105 cm−1 and 2.16×105 cm−1 for pointed and 3.2×104 and 1.74×104 for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical applications in field-emission-based electron sources. [ABSTRACT FROM AUTHOR]

Maxwell–Wagner relaxation dominated Al2O3/TiO2 nanolaminates (ATA NLs) have recently demonstrated their potential for high-density energy storage applications. In this report, we have unraveled the defect-mediated transport mechanisms prevailing in Al2O3/TiO2 sub-nanometric laminates. Temperature-dependent ac conductivity measurements revealed the signature of small polaron hopping in TiO2 active layers and trap-assisted tunneling transport through Al2O3 barrier layers, which was corroborated by resonant photoelectron spectroscopy and temperature-dependent current–voltage measurement. The polaronic defect states, found ∼1 eV below the Fermi level, served as the hopping centers and leakage paths for current. The signature of quantum tunneling transport and the negative differential conductance observed toward higher electric field was attributed to the splitting of delocalized minibands. These transport properties of Al2O3/TiO2 nanolaminates will help in tailoring these materials for next-generation storage capacitors. [ABSTRACT FROM AUTHOR]

The resistive switching phenomenon is attributed to local formation and rupture of conductive filaments (CF), however some aspects of the switching mechanism still need wider consensus. The origin of resistance contribution to low resistance state (LRS) and high resistance state (HRS) is although well known, the origin of capacitive contribution to the memory state of resistive random access memory device (RRAM) is ambiguous. Here we report impedance spectroscopic studies carried on Cu/TiO 2 /Pt devices to address the origin of resistive and capacitive contribution, where the effect of DC bias voltage, reset stop voltage and set compliance current on the impedance of RRAM memory states were investigated in detail. The studies revealed that the capacitive contribution was dominated by the surrounding TiO 2 bulk and contrary to existing knowledge, gap formed owing to ruptured CF has negligible role. These studies also reaffirmed the origin of the resistive contribution to the HRS and LRS state, which was dictated by the ruptured gap and connected CF, respectively. Results of this study may be significant towards improving the switching time and operating frequency performance of futuristic memory, RF switch and neuromorphic computing applications of RRAM devices. [ABSTRACT FROM AUTHOR]

Photodetectors based on n‐Mg0.25Zn0.75O/p‐Si heterojunctions are not only suitable for integration with existing semiconductor technology, but also circumvent the difficulty of stable p‐type doping in MgxZn1–xO. However, the use of Si leads to photoresponse in the visible part of the light spectrum, which renders n‐MgxZn1–xO/p‐Si heterojunction devices unsuitable for visible blind UV photodetection. Herein, it is demonstrated that the visible photoresponse in the n‐Mg0.25Zn0.75O/p‐Si photodetectors can be significantly suppressed by inserting a thin interlayer of MgO at the heterojunction. The MgO layer serves as a blocking layer for the drift of photo‐excited electrons from p‐Si to n‐Mg0.25Zn0.75O, thereby limiting the visible photoresponse. It is found that on increasing the thickness of the MgO interlayer from 3 to 15 nm, the UV to visible rejection ratio increases from ≈25 to 200. This enhancement in the UV to visible rejection ratio demonstrates that n‐Mg0.25Zn0.75O/p‐Si heterojunction devices with MgO interlayer are promising for visible‐blind UV photodetection applications. [ABSTRACT FROM AUTHOR]

Piezoelectric nanogenerators (PENG), which convert random mechanical energy into electrical energy, have attracted considerable attention due to their application potential in self-powered micro and nano electronics devices, wearable electronics, sensors etc. PENGs based on ZnO nanostructures are particularly important due to their low cost, flexibility and bio-compatibility. Flexible PENGs based on ZnO nanostructures dispersed in Polydimethylsiloxane (PDMS) in ITO/ZnO:PDMS/ITO device configuration were fabricated and characterized for vibration energy harvesting applications. Surfactant free ZnO nanostructures were grown using co-precipitation route and ZnO:PDMS nano-composite films with ZnO content varying in the range of 1.5–7.5 wt% were deposited on ITO/PET substrates for PENG fabrication. The maximum open circuit voltage and short circuit current of ~ 2.5 V and ~ 4 µA respectively were obtained in PENG fabricated with 6 wt% ZnO. The output characteristics were further enhanced to 5 V and 6 µA with flowing oxygen ambient annealing of ZnO nanostructures generating an instantaneous power density of ~9.55 µWcm−2. X-ray photoelectron spectroscopy studies confirmed reduction in oxygen vacancy and enhancement in oxygen interstitial concentrations on oxygen annealing which leads to the suppression of free carrier induced internal screening in ZnO nanostructures. This suppression of internal screening effect is the possible reason for the enhancement in output characteristics of ZnO:PDMS PENG fabricated with oxygen annealed ZnO nanostructures. The electrical energy generated by the ZnO:PDMS PENG was rectified and effectively stored in capacitors and used to power LEDs and LCD display. • ZnO nanostructures were grown by co-precipitation method with air and oxygen annealing. • ZnO:PDMS PENG with variable wt% of ZnO in PDMS were fabricated in ITO/ZnO:PDMS/ITO configuration. • The output performance of ZnO:PDMS PENG is improved significantly by annealing ZnO nanostructures in flowing oxygen ambient. • XPS established a correlation between the oxygen related point defects in ZnO and output characteristics of ZnO based PENG. • The output energy from ZnO:PDMS PENG was rectified and effectively stored in capacitor to flash LEDs and LCD display. [ABSTRACT FROM AUTHOR]

We report the photovoltaic properties of doped ferroelectric [Bi0.9La0.1][Fe0.97Ti0.02Zr0.01]O3 (BLFTZO) thin films. Polycrystalline BLFTZO films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition technique. Al-doped ZnO transparent top electrodes complete the ZnO:Al/BLFTZO/Pt metal-ferroelectric-metal capacitor structures. BLFTZO showed switchable photoresponse in both polarities. The open circuit voltage (VOC) and short circuit current (JSC) were found to be ~0.022 V and ~650 μA/cm², respectively after positive poling, whereas significant difference in VOC ~ 0.018V and JSC ~ 700 μA/cm² was observed after negative poling. The observed switchable photocurrent and photovoltage responses are explained on the basis of polarization flipping in BLFTZO due to the applied poling field. [ABSTRACT FROM AUTHOR]

Abstract: We report valence and conduction band offset measurements in a pulsed laser deposited Ni0.07Zn0.93O/ZnO heterostructure using X-ray photoelectron spectroscopy, valence band spectroscopy and ultraviolet visible spectroscopy. Neglecting the strain effect, the valence band offset was estimated to be 0.32 eV and the conduction band offset comes out to be −0.23 eV. Ratio between conduction band and valence band offset is 0.72. Core level shifting due to Ni doping has also been explained. Magnetotransport study of Ni0.07Zn0.93O film reveals that the charge carriers might be spin polarized at the interface of the heterojunction. [Copyright &y& Elsevier]

The room temperature crystal structure of potential high- k dielectric LaGdO3 has been analyzed by X-ray diffraction techniques and its structural evolution with temperature has been probed by Raman spectroscopy. Rietveld refinement of the ambient XRD data established the perfectly layered B-type monoclinic crystal structure with a = 14.43 Å, b = 3.68 Å, c = 8.99 Å, and β = 100.57° which is further validated by the 21 (14 Ag and 7 Bg) Raman-active vibrational modes with centro-symmetric space group [ABSTRACT FROM AUTHOR]

With the rapid development of new device miniaturization technology, there is invigorated interest in magnetic nanostructures for potential application in novel multifunctional devices. In continuation to our search for a suitable magnetic material having Curie temperature (Tc) well above room temperature for multifunctional applications, we have studied the dielectric, optical, magnetic, and resistance switching characteristics of Ni0.65Zn0.35Fe2O4 (NZFO) thin films. The observation of only (004) reflection in the X-ray diffraction patterns confirms the c-axis orientation and high quality growth of NZFO thin films. The presence of mixed valences of Fe2+/Fe3+ cations is probed by X-ray photon spectroscopy, which supports the cationic ordering-mediated large dielectric response. Our investigations reveal NZFO to be an indirect band gap material (~1.8eV) with a direct gap at ~2.55eV. These nanostructures exhibit high saturation magnetization and a low coercive field with a ferrimagnetic-paramagnetic phase transition of ~713K. Magnetic force microscopy studies revealed the stripe-like domain structure of the investigated thin films. In addition, these thin films exhibit reliable and repeatable unipolar resistive switching characteristics. The observed high dielectric permittivity with low loss tangent, large magnetization with soft magnetic behavior, striped magnetic domain structure and reliable resistance switching in NZFO thin films above room temperature suggest potential application in memory, spintronics, and multifunctional devices. [ABSTRACT FROM AUTHOR]

Abstract: Lanthanum hexaboride films were grown on tungsten and rhenium tips and foils by pulsed laser deposition. The X-ray diffraction spectra of the PLD films on both the substrates show crystalline nature with average grain size . The field emission studies of pointed and foil specimens were performed in conventional and planar diode configurations, respectively, under ultra-high vacuum condition. An estimated current density of was drawn at the electric field of and from the coated tips of tungsten and rhenium, respectively. The Fowler–Nordheim plots were found to be linear showing metallic behavior of the emitters. The field enhancement factors were calculated from the slopes of the Fowler–Nordheim plots, indicating that the field emission is from nanoscale protrusions present on emitter surfaces. The emitters were operated for long time current stability (3h) studies. The post-field emission surface morphology of the emitters showed no significant erosion of films during 3h continuous operation. The observed behavior indicates that it is linked with the growth of films on W and Re. These results reveal that the films exhibit high resistance to ion bombardment and excellent structural stability and are more promising emitters for practical applications in field emission based devices. [Copyright &y& Elsevier]

High-pressure synchrotron based angle dispersive x-ray diffraction (ADXRD) studies were carried out on SmGdO3 (SGO) up to 25.7 GPa at room temperature. ADXRD results indicated a reversible pressure-induced phase transition from ambient monoclinic to hexagonal phase at ∼8.9 GPa. The observed pressure-volume data were fitted with the third order Birch-Murnaghan equation of state yielding zero pressure bulk modulus Bo=132(22) and 177(9) GPa for monoclinic (B-type) and hexagonal (A-type) phases, respectively. Pressure dependent micro-Raman spectroscopy further confirmed the monoclinic to hexagonal phase transition at about 5.24 GPa. The mode Grüneisen parameters and pressure coefficients for different Raman modes corresponding to each individual phases of SGO were calculated using pressure dependent Raman mode analysis. [ABSTRACT FROM AUTHOR]

Herein, diode characteristics of n‐MgxZn1−xO/p‐Si heterojunctions grown by pulsed laser deposition at different oxygen ambient pressures are investigated. It is found that the heterojunctions grown at lower oxygen growth pressure of 1.0 × 10−2 mbar and below do not show rectifying diode‐like behavior, whereas those grown at higher oxygen pressures at and above 2.5 × 10−2 mbar exhibit perfect diode‐like rectifying characteristics. The diode characteristics are found to improve significantly with increasing oxygen ambient pressure during the growth of MgxZn1−xO film. The current–voltage measurements show that the n‐MgxZn1−xO/p‐Si heterojunction diode grown at a higher oxygen ambient pressure of ≈1.0 × 10−1 mbar has the lowest reverse saturation current of ≈19 nA and highest rectification ratio of ≈1.4 × 104. The capacitance–voltage measurements reveal that the depletion layer width of heterojunction diodes increases manifold with increasing oxygen ambient pressure during the growth of MgxZn1−xO, which is understood in terms of decrease in carrier concentrations in the MgxZn1−xO thin films grown at higher oxygen ambient pressures. The n‐MgxZn1−xO/p‐Si heterojunction diodes, grown at high oxygen ambient pressures, with low reverse saturation current, high rectification ratio, and large depletion width may have potential application in wide‐bandgap nanoelectronic devices and UV enhanced photodetectors. [ABSTRACT FROM AUTHOR]

We report magnetoelectric coupling and Raman spectroscopic studies on [(1 - x)Pb(Fe0.5Nb0.5) O3-xNi0.65Zn0.35Fe2O4] (x=0.20) PFN-NZFO composite. Apart from the presence of zone centre Raman active modes of the parent compound, some new peaks are observed in the low frequency region. The electric field controlled peak position (∼48 cm-1) suggests that this mode is of magnetic origin. From temperature dependent Raman scattering studies, temperature coefficients for phonons of different symmetries were estimated. Our measurements on electrical control of magnetic order and magnetic control of electrical order confirmed the existence of converse and direct magnetoelectric coupling in this composite at room temperature. [ABSTRACT FROM AUTHOR]

Multilevel cell (MLC) capability of a memory device is an attractive alternative to realise high integration density of memory arrays. In addition, power efficient memory cell along with MLC capability has huge potential in neuromorphic computing and data storage applications. In this study low power, high speed and 3-bit multilevel bipolar resistance switching operation is reported in TiO2 thin films where copper is used as counter electrode. On account of using an oxidisable electrode, low programming voltages (∼+0.2 V, −0.1 V) along with low reset current (∼10 µA) are observed, thereby ensuing low power (∼µW) memory operation. Additionally, observation of fast switching (∼250 ns) translated to ultra-low energy (∼pJ) consumption. By varying compliance current (IC) from 25 µA to 1.6 mA during the set process, eight distinct non-volatile resistance states are reliably obtained, which showed statistically significant and non-overlapping resistance distribution. The multilevel resistive switching in Cu/TiO2/Pt device is explained by considering filamentary the widening phenomenon in the electrochemical metallization memory cell. Numerical calculations revealed that increase in the diameter of the metallic conducting filament from ∼3 nm to 70 nm with increasing IC is accountable for multiple low resistance states. The results of this study are promising towards realisation of emerging memory devices with low operating power, fast switching operation and high spatial density. [ABSTRACT FROM AUTHOR]

Herein, it is shown that the UV photoresponse characteristics of MgZnO thin films deposited by pulsed laser deposition change rapidly with time if the films are exposed to ambient air and that the response can be stabilized significantly by depositing a thin capping layer of MgO on the surface of MgZnO thin film. The decay time of photocurrent in as‐deposited MgZnO thin films increases from 1.8 to 229 s and the value of peak responsivity increases by about three orders of magnitude as the film is exposed to air for about 106 s. On application of MgO capping layer, the decay time of the photocurrent marginally increases from ≈0.2 to ≈0.4 s and the value of peak responsivity increases only by one order of magnitude over the span of 106 s, thereafter showing tendency of saturation, implying much better stability in performance. The MgO capping layer is transparent to UV, but acts as a diffusion barrier for oxygen, stabilizing the UV photoresponse. [ABSTRACT FROM AUTHOR]

The increasing demand of energy harvesting and wearable electronics applications requires the development of flexible and highly durable piezoelectric nanogenerators (PENG). In this work, We have fabricated flexible ZnO:PVDF based PENGs for vibrational energy harvesting and shoe insole pedometer application s. ZnO nanorods were grown by hydrothermal method and incorporated into PVDF matrixes in the concentration range of 5–15 wt%. These homogeneous ZnO:PVDF composite films were sandwiched between Al electrodes to realize flexible free standing PENGs. The open circuit voltage (Voc), short circuit current (Isc) and instantaneous power density of PENGs increased from ∼ 4 V, 0.4 µA and 1.6 µW/cm2 to ∼ 14.6 V, 0.6 µA and 21.3 µW/cm2 respectively when ZnO nanorods concentration in PVDF increased from 0 to 10 wt% and decreased with further increase in ZnO nanorods concentration. The enhancement in output characteristics of ZnO:PVDF PENG with increasing ZnO concentration was attributed to β-phase crystallization of PVDF, which was confirmed by XRD and FTIR measurements. The deterioration in output characteristics beyond 10 wt% of ZnO nanorods concentration was explained considering the variation of dielectric constant and remnant polarization. The rectified output of the PENGs was effectively stored in various commercially available capacitors and used to power LEDs and stopwatch displays. The PENG with 10 wt% ZnO concentration was used to develop shoe insole pedometer which was interfaced with android based mobile application via Bluetooth. The shoe insole pedometer was successfully tested for 5000 steps at different walking frequencies ranging from 0.5 Hz to 2 Hz in the speed range of ∼ 1.4 km/h to 5.5 km/h. This study not only gives an insight into the mechanism of ZnO:PVDF based PENGs but also opens up their potential in vibration energy harvesting and shoe insole pedometer applications. • ZnO:PVDF based flexible piezoelectric nanogenerators (PENGs) were fabricated with variable ZnO nanofiller concentrations. • The variation of output performance of ZnO:PVDF based PENGs was studied with ZnO nanofiller concentrations. • The PENGs were able to power capacitors, LEDs, and LCDs. • A pedometer device has been fabricated using the ZnO:PVDF based flexible PENG sensor. [ABSTRACT FROM AUTHOR]

We report unipolar resistive switching suitable for nonvolatile memory applications in polycrystalline BiFeO3 thin films in planar electrode configuration with nonoverlapping Set and Reset voltages, On/Off resistance ratio of ~104 and good data retention (verified for up to 3,000 s). We have also observed photovoltaic response in both high and low resistance states, where the photocurrent density was about three orders of magnitude higher in the low resistance state as compared to the high resistance state at an illumination power density of ~100 mW/cm². Resistive switching mechanisms in both resistance states of the planar device can be explained by using the conduction filament (thermo-chemical) model. [ABSTRACT FROM AUTHOR]

As the semiconductor technology approaches size limitation (according to Moore's law), significant efforts need to be focused to develop alternative gate dielectric materials that can facilitate low electrical functional thicknesses for future logic and memory nodes. Over the last few years there has been considerable interest in the application of inter‐lanthanide compounds in modern electronic devices. Researchers at University of Puerto Rico led by Professor Ram S. Katiyar have developed a novel alternative low‐loss high‐k dielectric lanthanum gadolinium oxide in their laboratory which is a significant development for nano‐electronic device applications, such as dynamic random access memories (DRAMs), resistive switching memory elements (RRAMs) and related logic electronic components (MOSFETs). Pavunny et al. (pp. 131–139) utilized X‐ray crystallography and Raman spectroscopy to characterize the crystal structure of this oxide and also discussed its high‐temperature phase transition near 900 K. This new material has a dielectric constant greater than five times that of silicon oxide which is higher than that of any of the presently used hafnium‐based high‐k dielectrics. Therefore it can have a broader impact on feature size reduction in the fabrication of CMOS logic and memory devices. [ABSTRACT FROM AUTHOR]

We report photovoltaic (PV) effect in multiferroic Bi0.9Sm0.1Fe0.95Co0.05O3 (BSFCO) thin films. Transition metal modified polycrystalline BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2/Si substrate successfully through pulsed laser deposition (PLD). PV response is observed under illumination both in sandwich and lateral electrode configurations. The open-circuit voltage (Voc) and the short-circuit current density (Jsc) of the films in sandwich electrode configuration under illumination are measured to be 0.9 V and −0.051 µA cm−2. Additionally, we report piezoresponse for BSFCO films, which confirms ferroelectric piezoelectric behaviour. [ABSTRACT FROM AUTHOR]

The paper deals with the comparative study of nanocrystalline Lanthanum hexaboride (LaB) thin films grown on various substrates by Pulsed laser deposition and Arc plasma method. Field emission studies were carried out on LaB films deposited on various substrates show metallic behavior of the emitters. The high value of field enhancement factors, indicating that the electron emission from LaB nanoscale protrusions deposited on emitter surface. The post field emission surface morphology of the emitters showed no significant erosion of the films during continuous operation. The observed behavior indicates that it is linked with the growth of LaB films on substrate crystal structure. The LaB nanocrystallites/nanowires films were synthesized using arc plasma method shows good emission current stability. The LaB micro/nanocrystallites were also obtained by picosecond laser irradiation which gives high enhancement β factor, and good emission current stability along with high current density. The results reveal that nanocrystalline LaB films, exhibit high resistance to ion bombardment and excellent structural stability and are more promising emitters for practical applications in field emission based new generation devices. [ABSTRACT FROM AUTHOR]

Abstract: Lanthanum hexaboride (LaB6) films have been deposited on a zirconium foil by pulsed laser deposition method. The field emission studies of the LaB6 deposited film have been performed in the planar diode configuration under ultra high vacuum conditions. The Fowler–Nordheim plots were found to be linear in accordance with the quantum mechanical tunneling phenomenon. A typical field emission current of 7.02μA was drawn at an applied electric field of 2V/μm. The field enhancement factor is calculated to be 8913cm−1, indicating that the field emission is from nanoscale protrusions present on the emitter surface. The atomic force microscope (AFM) investigation of the surface clearly shows the conical shaped nanoprotrusions of few hundred nanometers with asperities of 20–40nm on its top. The emission current–time plot recorded at the pre-set value of emission current of 5μA over a period of more than 3h exhibits an initial increase and subsequent stabilization of the current. The results reveal that the LaB6/Zr field emitter obtained by the pulsed laser deposition (PLD) is a promising cathode material for practical applications in field emission-based devices. [Copyright &y& Elsevier]

Abstract: A novel highly transparent intrinsic zinc oxide (ZnO) thin films (without adding any dopants and annealing) were grown by pulsed laser deposition (PLD) technique using Johnson Matthey “specpure”- grade ZnO pellets. The effects of substrate temperatures on zinc oxide thin film growth, optical transmission, absorption, reflection and photoluminescence properties were studied. As well as the feasibility of developing high quality transparent oxide thin films was also studied simultaneously. The optical transmission window of such obtained films, i.e., T% (max)⩾95% is broader than those of other transparent conducting oxides such as indium tin oxide (ITO) and absolute rivals that of the most transparent conducting oxides (TCOs). Also as a novelty merit, we want to emphasize as a interesting, significant and novel physical effect that the average optical transmittance of ZnO thin films rivals that of the most transmittive TCO films reported to date for this conductivity level (of the order of 103 Ω−1 cm−1). Also this is the first time that we have applied these PLD prepared ZnO thin films to iso and hetero semiconductor–insulator–semiconductor (SIS) type solar cells as transparent conducting oxide (TCO) coatings. From optical studies, we know that the films were act as highly anti-reflective coatings. From photoluminescence study, we confirmed the purity and high electrical conductivity of the deposited thin films of ZnO. The optical parameter values for the films were calculated, tabulated and graphically emphasized. Supplementary studies on surface, electrical, structural and internal morphological properties of zinc oxide thin film growth correlated with optical transmission, absorption, reflection and photoluminescence properties gives added advantages to this work. We hope that surely these data should be helpful either as a scientific or technical basis in the semiconductor processing and technology. [Copyright &y& Elsevier]

Abstract: In this present work, the effects of various substrate temperatures and various substrates on Zinc Oxide (ZnO) thin film growth and on surface morphological properties were studied. To the best of our knowledge this is the first time that laser molecular beam epitaxy (L-MBE), i.e., pulsed laser deposited (PLD) zinc oxide (ZnO) thin films on semiconductor wafers have been applied to Semiconductor–Insulator–Semiconductor (SIS) type multi-junction solar cells, as wide band-gap transparent conducting oxide (TCO) front electrode window layers, compatible with current semiconductor processing techniques. As well as our main aim, the feasibility of developing highly nano-tectured thin films was also studied simultaneously. The surface morphological and film growth characteristics of ZnO thin films laser deposited on to various substrates like glass, Silicon (Si), Gallium Arsenide (GaAs) and Indium Phosphide (InP) at various substrate temperatures like room temperature, 200°C and 300°C using ZnO pallets as targets are very novel, intelligent and significant from reported so for. The deposition process was optimized. The micro- and nano-scale photo-graphs of Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) showed the improvements of crystalline and surface nature of ZnO thin films with respect to various substrate temperatures and substrates. Better surface architecture was observed for thin films deposited at 300°C than RT, 200°C and on InP than Si and GaAs. Increasing the substrate temperature leads the films to fine nano-structure world. The results were discussed in detail. Thus we have developed a novel nano-architecture to obtain high quality ZnO nano-crystalline semiconductor thin films of different nano-scale grain sizes on glass and Si, GaAs and InP semiconductor single crystal wafers by using different substrate temperatures and substrates as controlling tools as value in practical nano-robotic (machining) device fabrication efforts. [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]

Titanium dioxide (TiO2)-based gate insulators for MOSFETs are of current interest in VLSI technology due to the high permittivity (k) of TiO2. In this paper, we present a study of metal–TiO2–SiO2–Si (MTOS) capacitors with equivalent dielectric thickness (EDT) in the range of 36–130 A˚. Pulsed laser deposition (PLD) of TiO2 to realize this stacked dielectric is being reported for the first time. Interestingly, it has been observed that even though an additional TiO2 layer has been deposited, the capacitance of the MTOS structure actually increases or remains almost the same compared to the MOS device having the same SiO2 layer thickness. Secondary ion mass spectrometric (SIMS) analysis reveals that there is substantial penetration of titanium into the underlying SiO2 layer resulting in a reduction of EDT. In addition, the leakage current of the MTOS capacitor reduced by almost two orders of magnitude and the breakdown field strength nearly doubled after incorporating the TiO2 layer. Thus, PLD is shown to be a viable technique for controlled deposition of TiO2 to achieve lower EDT with smaller leakage current, the two most desirable parameters in present-day MOS devices. [Copyright &y& Elsevier]

Lanthanum hexaboride films have been deposited on a tungsten tip by pulsed laser deposition technique. The field emission studies have been performed in the conventional field emission geometry. The Fowler-Nordheim plot obtained from the current-voltage characteristic is found to be linear in accordance with the quantum mechanical tunneling phenomenon. A current density of 1.2×104 A/cm2 is drawn from the deposited tip. The field enhancement factor is calculated to be 5537 cm-1, indicating that the field emission is from nanoscale protrusions present on emitter surface. The emission current-time plots show the very good stability of the emitter. [ABSTRACT FROM AUTHOR]

In this work, metal-TiO2–SiO2–Si (MTOS) capacitors have been fabricated where the TiO2 layers have been deposited by the pulsed laser deposition technique followed by annealing at different temperatures. MTOS devices with an effective dielectric thickness (EDT) as low as 1.6 nm and very low leakage current have been realized by using a two-step deposition process in which a buffer layer of TiO2 has first been deposited at 300 °C. This was followed by deposition and annealing of TiO2 at 750 °C. It has also been shown that the annealing temperature plays a significant role in determining the EDT of the dielectric film as well as the electrical characteristics of the MTOS capacitors. [ABSTRACT FROM AUTHOR]