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This work presents detailed characterization of structural, optical and electrical properties of Al doped ZnO (AZO) coated Corning® Willow® Glass substrate as a function of AZO thickness. It has been observed that the carrier concentration increases and the sheet resistance decreases as the thickness of the coating increases. A sheet resistance as low as ∼7 Ω/sq has been achieved for a 500 nm AZO coated flexible glass substrate with average 90% transparency in the visible region. The figure of merit (FOM) value as high as 7.4×10−2 Ω−1 has been calculated. The electrical as well as optical results are quite excellent and even better or comparable to those of commercial ITO and FTO substrates. The performance of the flexible substrate as transparent electrode for an a-Si:H solar cell has been demonstrated.

Graphene quantum dots (GQDs) synthesized by a direct chemical method have been used in combination with ZnO nanowires (NWs) to demonstrate their potential as a solar harvesting material in photovoltaic cells exhibiting an open circuit voltage of 0.8 V. The excited state interaction between the photoexcited GQDs and the ZnO NWs has been verified from the charge-transfer process by both emission spectroscopy and photovoltaic measurements. This work has implications for less expensive and efficient next generation solid-state solar cells.

A detailed study on the emission properties of ZnO nanorods/Ag nanoparticles for various concentrations of Ag has been presented. The photoluminescence (PL) spectra show that the near band edge (NBE) luminescence of ZnO is enhanced 10 times after Ag loading leading to an ultraviolet/visible emission ratio to 12.2 compared to a value of 1.2 for pristine ZnO nanorods. The enhancement in PL intensity is due to surface plasmon resonance coupling of the NBE emission between Ag and ZnO. We further confirm that morphology and/or surface modification do not contribute to this large increase in the band edge emission.

Synthesis of various nanostructured semiconductor materials and processing them for different device fabrications has been at the forefront of research for the last two decades. In comparison to spherical nanoparticles, anisotropic materials e.g. nanorods, nanowires, and nanodisks have been widely explored to obtain a better performance of the devices. In addition, it is also well-known that nanomaterials, on doping with suitable impurities, can enhance the device sensitivity and speed. Combining both, we report here the synthesis of micrometer long In2S3 nanosheets and on doping them with Cu(I), we have studied here their photoresponse properties. These nanosheets are synthesized in a high temperature colloidal method following a catalytic thermal decomposition of a single source precursor of In and S. From various TEM, HRTEM, and HAADF images the growth pattern of these sheets is investigated, and the obtained moire fringes at the overlapped region are discussed. Finally, the comparative study of the de...

The well-ordered metal oxide nanostructures can be synthesized successfully, but the conductance of these structures is limited, which is a disadvantage for applying these in photovoltaic and display devices. Conductivity of a semiconductor can be improved by using metal doping, but the issue becomes a major challenge in nanostructures since their high surface energy usually hinders any metal doping process. Here we show an entirely new metal-free doping strategy to enhance the current conduction of ZnO nanorods' (NRs) arrays through a sulphidation technique. The process is based on the electronegativity difference between S and O because of which one can expect a rigorous bond rearrangement at the interface and a ZnOS-ZnS composite is formed as O is being partially replaced by S. The current conduction by the metal oxide NRs arrays is significantly enhanced by nearly 4 orders of magnitude without sacrificing the transparency of the NRs arrays. The increased current conduction is assigned due to an increase in the Zn(i) concentration as evidenced from the electron paramagnetic resonance measurements. The composite layer grown on p-Si forms a photodiode which is highly sensitive to visible light with a very fast response time.

The steady state and time resolved spectroscopic studies reveal that two xanthene dyes Rhodamine 6G (R6G) and Rhodamine B (RB), used in the present investigations, form ground state hydrogen -bonded complexes with meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP). However, it is apparent that upon photoexcitation the H-bonding complexes formed in the ground state decompose into the individual reacting components. This presumption was confirmed from the observation of the presence of only static quenching mode in the steady state fluorescence of the dyes in presence of porphyrin. The photoelectrochemical properties of the free dyes and the mixtures of each dye with porphyrin are investigated by measuring incident photon-to-current conversion efficiency (IPCE) using ZnO electrode and also with TiO2 electrode. It is seen that Rhodamine B-porphyrin mixture has attained maximum IPCE among the four samples studied at approximately 550 nm using ZnO electrode. Using TiO2 electrode, slight improvement in the value of IPCE was found for the same mixture. Therefore Rhodamine B-porphyrin mixture may act as a good sensitizer for converting solar energy to electrical energy.

In this article, we have decorated multiwalled carbon nanotubes (MWCNTs) scaffold with ZnO quantum dots (QDs, size in the range of 2.9–4.5 nm) and investigated their prospects for photovoltaic applications. ZnO QDs, in the present study, work as photosensitizer instead of electron transporting media as used in recent conventional strategic solar cells. ZnO QDs/MWCNTs composite shows an increased visible absorbance and quenching of the broad visible emission at around ~560 nm, while only ZnO QDs exhibit a strong visible emission. An efficient electron–hole separation facilitates an increase in the short-circuit current. These results show a possibility of developing a nontoxic, ZnO QDs sensitized MWCNTs composite-based photovoltaic solar cell.

ZnO–SiO 2 core–shell nanorod (NRs) composites have been synthesized using a chemical method by varying the number of SiO 2 coating between one and ten, and their optical and photoconductivity properties have been investigated. Ultraviolet (UV) to visible emission peak intensity of the composites is increased as compared to pristine ZnO NRs, being maximum for the five times coated NRs due to the reduction of surface states. The same composite shows about an order of magnitude increase in the UV photosensitivity. The carrier relaxation during steady-state UV illumination decreases as the number of shell coating increases.

ZnO nanoparticles in the form of quantum dots (QDs) have been dispersed in SiO(2) matrix using StÖber method to form ZnO QDs-SiO(2) nanocomposites. Addition of tetraethyl orthosilicate (TEOS) to an ethanolic solution of ZnO nanoparticles produces random dispersion. On the other hand, addition of ZnO nanoparticles to an already hydrolyzed ethanolic TEOS solution results in a chain-like ordered dispersion. The photoluminescence spectra of the as-grown nanocomposites show strong emission in the ultraviolet region. When annealed at higher temperature, depending on the sample type, these show strong red or white emission. Interestingly, when the excitation is removed, the orderly dispersed ZnO QDs-SiO(2) composite shows a very bright blue fluorescence visible by naked eyes for few seconds indicating their promise for display applications. The emission property has been explained in the light of structure-property relationship.

We have sputtered Zn onto quasi-one-dimensional ZnO nanowires (NWs) in order to investigate the effect of Zn diffusion on the photoluminescence and photoconduction properties of ZnO NWs. Elemental mapping clearly indicates higher Zn concentration in the NWs due to diffusion of Zn. The Zn-sputtered NWs show an enhanced ultraviolet emission with 7 nm red shift. Since the ionization energy of Zni is 51 meV, the enhanced PL emission with a red shift is correlated to the coupling between free exciton and zinc interstitials (Zni) defects. The photocurrent transients show almost 20 times more photocurrent generation in Zn/ZnO NWs compared to the as-grown NWs. In contrast, the thin film shows no significant change in the photoluminescence and photoconductivity. Based on the photoconductivity and photoluminescence results, we predict that Zn diffusion in the NWs occurs easily compared to the films because of the smaller dimensions of the NWs.

New wormhole-like mesoporous TiO 2 material has been synthesized through a convenient sol–gel method in the presence of a Schiff base secondary amine hexadecyl-2-pyrrole-methylamine (HPMA) containing chelating donor sites as template or structure directing agent (SDA). SDA molecules can be easily removed from the composite to generate mesoporosity and upon removal of the SDA molecule, this mesoporous TiO 2 material showed very high surface area (480 ± 10 m 2 /g) with an average pore diameter of 2.57 ± 0.05 nm. When Rose Bengal dye is entrapped inside the nanopores of this material, it showed a drastic enhancement ( ca . 40-folds) in the photoconductivity vis-a-vis mesoporous TiO 2 alone under white light illumination.

We study the change in the structural morphology and optical properties of aqueous solution grown ZnO microrods on glass substrates with the change in the concentration of hexamethylene tetramine (HMT). The field emission scanning electron microscope images of the microrods grown for equimolar (1:1) ratio of Zn2+ salt and HMT exhibit the highest aspect ratio, 8.3, which decreases gradually, while the relative intensity of the (100) peak in the X-ray diffractogram increases with increase in the HMT concentration. The change in the morphology from a perfect hexagonal to an oval-shaped needle is experimentally supported by the high-resolution transmission electron microscope results. A sharp and strong ultraviolet photoluminescence peak ensures good structural quality of the microrods for the molar ratios 1:1 and 1:3 above which the quality degrades. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A series of n-ZnO/p-Si thin film heterojunctions have been fabricated by a low cost sol–gel technique for different ZnO film thicknesses and the dark as well as photo current–voltage (I–V) characteristics have been investigated in details. The heterojunction with ZnO thickness of 0.46 μm shows the best diode characteristics in terms of rectification ratio, IF/IR = 5.7 × 103 at 5 V and reverse leakage current density, JR = 7.6 × 10−5 A cm−2 at −5 V. From the photo I–V curves and wavelength dependent photocurrent of the heterojunctions, it is found that the junction with 0.46 μm ZnO thickness shows the highest sensitivity towards both UV and visible lights.

ZnO thin films are deposited on the glass substrates by sol–gel drain coating technique by varying the concentration of the sol. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used to investigate the effect of sol concentration on the crystallinity and surface morphology of the films. The results show that with increase in sol concentration, the value of full width at half maximum (FWHM) of (0 0 2) peak decreases while the strain first increases and then decreases. The sol with higher concentration results in the increase in the grain size. The studies on the optical properties show that the band gap value increases from 3.27 to 3.3 eV when the sol concentration changes from 0.03 to 0.1 M. The photoconductivity studies reveal that the film for 0.05 M sol shows the maximum photoresponse for ultraviolet (UV) wavelength (

A series of Al doped ZnO (ZnO : Al) films with different Al concentrations have been deposited on glass substrates using the sol–gel spin coating technique and the effect of Al concentrations on the structural, electrical, optical and photoresponse properties have been investigated. The XRD results show the presence of peaks due to the reflections of the planes from a wurtzite type of ZnO structure. The surface morphology shows that the grains become non-uniform and smaller in size as the Al doping level increases. For 1–2% Al doping, the film attains highest carrier concentration of about ~2.7 × 1019 cm−3 and lowest resistivity of ~2 × 10−2 Ω cm. The excitonic nature in the absorption spectrum disappears for doping above 1%. The band gap increases with the increase in the Al concentration. The photoconductivity studies show that although the photoresponse properties are degraded due to incorporation of Al atoms, the 1% Al doped film shows the best photoresponse properties within the doping limit up to 5%.

A detailed investigation has been carried out to study the effects of growth temperature, NH3 flow rate, grinding-mediated annealing of the as-synthesized GaN powder, different substrates and Au catalyst on the products grown by a direct reaction of Ga with NH3. Nanowires of diameter in the range 15–40 nm are grown around a narrow temperature zone, 1000 °C < t < 1100 °C, with a 150 sccm NH3 gas flow rate. Beyond this temperature zone, GaN platelets are formed in a large scale. Annealing of the as-synthesized GaN powder at 800 °C after a grinding process results in the growth of dendrite-like GaN nanostructures and above 800 °C, only hillocks of GaN platelets are grown. The layers formed on sapphire and ZnO/quartz substrates consist of GaN nano- and microrods of diameter 40–100 nm and 1–1.5 μm respectively that show ultraviolet (UV) emission peaks below 400 nm. Large-scale synthesis of GaN nanorods of diameter 60–100 nm has been achieved on Au/quartz substrate at 1050 °C with a 150 sccm of NH3 gas flow rate. The nanorods exhibit a strong UV emission peak indicating a better optical quality. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A series of ZnO films of different thickness have been deposited on glass substrates using sol-gel technique by varying the number of spin coatings and the effect of film thickness on the structural, electrical and optical properties have been investigated. The XRD results indicate that the full width at half maximum (FWHM) of the (0 0 2) diffraction peak and the strain along c-axis are decreased as the film is grown up to a thickness of 300 nm. Above 300 nm, the strain again becomes appreciable. The surface morphology shows that the grains become more uniform and bigger in size as the film thickness increases. Electrical result shows that although ZnO film with thickness of around 260 nm has the highest resistivity but is better for current conduction. The excitonic nature in the absorption spectrum becomes prominent for a film with thickness of around 260 nm. The band gap increases and then decreases as the film grows thicker.

Mg x Zn1−x O (x = 0.0–0.20) ternary alloyed thin films have been deposited by sol-gel technique at 550 °C. The studies on the change in c-axis lattice parameter, PL spectra, optical absorption coefficient, and band gap values suggest that the solubility limit of MgO in Mg x Zn1−x O lies within the composition range 0.05

On the face of the impending energy crisis, developing low-energy or even zero-energy photoelectronic devices is extremely important. A multispectral photosensitivity feature of a self-powered device provides an additional powerful tool. We have developed an unprecedented high performance dual wavelength self-powered ZnO@CdS/PEDOT:PSS core-shell nanorods array photodetector through a simple aqueous chemical method wherein a suitable band alignment between an intelligent material pair, i.e. ZnO and CdS, has been utilized. Besides a noteworthy advantage of the devices being that they show a very sharp and prominent dual wavelength photosensitivity, both the ultraviolet and visible light sensitivity (ratio of current under illumination (Iphoto)/current under dark (Idark)) of the device are two orders of higher magnitude than those of pristine ZnO, attaining values of 2.8 × 10(3) and 1.07 × 10(3), respectively. At the same time, temporal responses faster than 20 ms could be achieved with these solution-processed photodetectors. The present study provides a very important direction to engineer core-shell nanostructured devices for dual wavelength high photosensitivity.

The dependence of photoconducting properties on the thickness of ZnO films deposited on glass substrates by sol–gel spin coating technique has been investigated. The X-ray diffraction (XRD) results indicate that the film with thickness of 260 nm becomes maximum oriented along (0 0 2) direction. The field emission scanning electron micrograph (FESEM) shows that the grain size and volume of micropore increases with increase in thickness. Calculation shows that 260 nm film has the highest porosity. The photoconductivity studies exhibit maximum photoresponse for ultraviolet (UV) wavelength (

A p-CuO/n-ZnO thin film heterojunction is fabricated on a glass substrate by the sol–gel technique. The crystallinity of the junction materials and microstructure of the top p-layer are examined by an x-ray diffractometer (XRD) and scanning electron microscope (SEM). The current–voltage (I–V) characteristics of the p–n heterojunction and its temperature dependence have been investigated in air and H2 ambient. Although the junction possesses linear I–V characteristics from room temperature (RT) to 150 °C in air, at higher temperatures (200 °C to 300 °C), it shows nonlinear rectifying behaviour. The forward current is greatly increased with increasing temperature while the reverse current is increased slightly resulting in a IF/IR ratio as high as 485. The ideality factor (n) is 4.88 at a temperature of 300 °C. The forward current is highly increased by the introduction of H2 gas at 300 °C. However, a simultaneous increase in the reverse current makes the IF/IR ratio 8.4. It is observed that H2 sensitivity of the heterojunction is increased with the increase in temperature as well as the thickness of CuO film. A sensitivity value as high as 266.5 is observed at 300 °C when biased at 3 V in the presence of approximately 3000 ppm of H2.

Effect of thermal annealing in different ambients on the structural, electrical and optical properties of the sol–gel derived ZnO thin films are studied. XRD results show that the annealed ZnO films with wurtzite structure are randomly oriented. Crystallite size, carrier concentration, resistivity and mobility are found to be dependent on the annealing temperature. The change in carrier concentration is discussed with respect to the removal of adsorbed oxygen from the grain boundaries. The highest carrier concentration and lowest resistivity are 8 × 10 18 cm −3 and 2.25 × 10 −1 Ω cm, respectively, for the film annealed at 500 °C in vacuum. The annealed films are highly transparent with average transmission exceeding 80% in the wavelength region of 400–800 nm. In all three ambients, the optical band gap value does not change much below 500 °C temperature while above this temperature band gap value decreases for nitrogen and air and increases for vacuum.

Hexagonal ZnO films deposited on quartz glass, sapphire and glass substrates by sol–gel coating are found to be randomly oriented; maximum randomness is found in the film on quartz glass substrate. All the films are ultra-violet (UV) sensitive at around 360 nm sensitivity being maximum for the film with maximum randomness in the crystallite orientations. The film on quartz showed the lowest dark current and maximum photoresponse, which is related to the lowering of the barrier heights, introduced by the adsorbed oxygen at the grain boundaries. Faster decay in photocurrent is observed for the film deposited on glass, which is attributed due to the smaller crystallite sizes with porous microstructure of the film.

The effect of substrate-induced strain in polycrystalline ZnO thin films on different substrate, e.g., GaN epilayer, sapphire (0001), quartz glass, Si(111)∕SiO2, and glass deposited by sol-gel process, has been investigated by x-ray diffraction, scanning electron microscope, electrical resistivity, and photoluminescence measurements. A strong dependence of orientation, crystallite size, and electrical resistivity upon the substrate-induced strain along the c axis has been found. The results of structural and morphological studies indicate that relatively larger tensile strain exists in ZnO deposited on sapphire and glass, while a smaller compressive strain appears in film deposited on GaN and the strain is relaxed in larger crystallite size. The electrical resistivity of the films increases exponentially with increasing strain. The excitonic peak positions are found to shift slightly towards lower energy side with increasing strain. The analysis shows that GaN being a closely lattice-matched substrate produces ZnO films of better crystallinity with a lower resistivity.

We report on the photoconductive UV detector on sol–gel synthesized ZnO film based on Au–ZnO metal–semiconductor junction. I – V characteristics of these devices are perfect Ohmic in nature. Photocurrent is maximum at around 350 nm, and later a more than two-fold drop in the value was measured above 400 nm. Room temperature photoluminescence spectrum of ZnO exhibits two peaks, one in the UV region and another in the visible region, the latter being dominated due to the presence of deep-level defect states. The responsivity is increased linearly with the bias voltage. The responsivity as high as 0.040 A/W and a quantum efficiency of 14% were achieved at 350 nm. The photoresponse decay in these devices is slow.

We report a low temperature Ti/Ni/Ti/Au multilayered Ohmic contact to n-type 6H-SiC bulk sample. By using this simple metallization scheme and annealing at 750 °C, a low contact resistance is achieved for vertical conduction. Similar contact scheme on polished and unpolished sides of the bulk SiC substrate showed a difference in resistance due to different surface roughness. X-ray diffraction results of the alloyed contact layer show that formation of TiSi2 layer might be responsible for the Ohmic contact. The roughness of the contact surface on the polished side and unpolished sides are found to be 5 and 38 nm, respectively.

ZnO nanorods (NRs) have been grown by aqueous chemical growth method (ACG) by varying only the position of the substrate and keeping other reaction parameters constant. The crystallinity of the ZnO nanorods is found to worsen as the substrate height increases from the bottom of the vessel resulting in structural defects those causes an enhanced ultraviolet emission.

The effect of different laser power on the structural, photoluminescence and transmittance properties of ZnO films grown using pulsed laser deposition technique has been described. It is observed that laser power influences the photoluminescence properties as the crystallinity of the transparent films changes.

The stripe geometry InGaN/GaN and InGaN/AlInGaN multiple quantum well light emitting diodes (LEDs) were fabricated using pulsed lateral epitaxial overgrowth and conventional GaN layers over sapphire. Material quality improvement due to overgrowth of GaN layer results in enhanced LED output power for broad area square geometry devices emitting at 430 nm. Using of stripe geometry edge emitting LEDs allows considerable reducing of the device differential resistance and improving of the output power density. The power enhancement and ease of thermal management makes the arrays of stripe geometry LEDs to be promising for high power applications.

Reactive ion etching (RIE) of GaN has been performed using BCl 3 and additives, Ar and N 2 , to BCl 3 plasma. The etch rate, surface roughness and the etch profile have been investigated. The etch rate of GaN is found to be 104 nm/min at rf power of 200 W, pressure of 2 Pa, with 9.5 sccm flow rate of BCl 3 . The addition of 5 sccm of Ar to 9.5 sccm of BCl 3 reduces the etch rate of GaN while the addition of N 2 does not influence the etch rate significantly. The RIE of GaN layer with BCl 3 /Ar and BCl 3 /N 2 results in a smoother surface compared to surfaces etched with BCl 3 only. The etched side-wall in BCl 3 plasma makes an angle of 60° with the normal surface, and the angle of inclination is more in cases of BCl 3 /Ar and BCl 3 /N 2 plasmas. The RIE induced damage to the surface is measured qualitatively by PL measurements. It is observed that the damage to the etched surfaces is similar for all the plasmas.

We have investigated the effect of thermal annealing on the diode characteristics of solution-processed novel core–shell coaxial n–p nanorods heterojunction consisting of n-type ZnO as a core and p-type CuS as a shell material. The values of turn-on-voltage, rectification ratio, reverse saturation current density, barrier height, and ideality factors have been improved as the as-prepared heterojunction is annealed at higher temperatures owing to the improvement in the interface between ZnO and CuS as evidenced from the high-resolution transmission electron microscopy. The X-ray diffraction results also confirm the improvement in the crystalline quality of ZnO and CuS through annealing. The experimental current–voltage data are consistent with the presence of dominating recombination-tunneling conduction occurring through the interface defect states between ZnO and CuS. The results demonstrate that an annealing process plays a dominant role in the interfacial defects which helps to modify the diode performance paving a way to cheaper electronic nanodevices.

We have fabricated an n-p nanorods (NRs) heterojunction consisting of n-type ZnO NR and p-type CuInS2 by a simple, low cost solution method through an ion-exchange route. The heterojunction shows a rectifying behavior with an ideality factor of 1.66. Furthermore, the heterojunction is promising candidates for applications in electro-optic devices.

Ag@SiO2/ZnO nanorods (NRs) heterostructures have been grown by chemical solution method in two steps. The band edge ultraviolet (UV) emission intensity of ZnO NRs has been enhanced four times as Ag@SiO2 nanoparticles are loaded on NRs' surface. The emission enhancement is due to surface plasmon resonance of the metal NPs facilitated by the SiO2 shell around it.

Low temperature solution growth of ZnO nanostructures carries immense technological importance. Vertically aligned ZnO nanorods (NRs) arrays have been grown on glass substrate at low temperature using zinc acetate di-hydrate, hexamethelene tetramine (HMT) and cetyl-trimethyl amonium bromide (CTAB) and their ultraviolet (UV) photosensitivity properties have been investigated. Hydrothermally grown ZnO NRs arrays show a very high UV-to-visible rejection ratio (112) with a sharp cut-off wave length at 400 nm in the photocurrent spectrum as compared to ZnO NRs grown by another low temperature technique using aqueous chemical growth (ACG) method. The hydrothermal NRs show extraordinarily high UV photosensitivity (photo-to-dark current ratio, 1.16×105) which is nearly one order of magnitude higher than that of ACG NRs. Analyses of growth-decay time constants, photoluminescence spectra, full width at half maximum for (002) x-ray diffraction peak indicate better crystalline quality which is responsible for the hig...

Aqueous chemically grown ZnO nanorods (NRs) are highly resistive. Sulphur (S) treatment of these NRs results in the formation of ZnOS-ZnS composite NRs. The room temperature photoluminescence spectra show quenched ultraviolet and enhanced visible emissions in the composites. For a sulphur treatment of 2.5 hrs, ZnOS-ZnS composite NRs show 3×103 times increase in the conductivity value as compared to that of the pristine NRs.

Ag-ZnO nanorods (NRs) have been grown by solution method by capping aqueous chemically grown ZnO NRs by solutions of Ag nanoparticles (NPs) with different concentrations. The band edge ultraviolet (UV) emission intensity of ZnO increases gradually as the Ag concentration increases and becomes 3.2 times higher than the pristine NRs. Also a 3.2 times enhanced UV photocurrent has been obtained in Ag-ZnO NRs.

A rapid dark thermal annealing process at 800 0C of radio frequency sputtered P doped ZnO thin films have resulted in improved electrical transport properties with hole concentration of 1 × 1018 cm-3, mobility 4.37 cm2/Vs and resistivity 1.4 Ω-cm. X-ray photoelectron spectroscopy shows the presence of inactivated P in as-grown ZnO films.

Information on the mechanistic differences in the luminescence properties of Ti/ZnO nanorods (NRs) has been obtained through the preparation of heterostructures by (a) varying the thickness of Ti from 1 nm to 20 nm keeping the substrate temperature at 400 °C, (b) varying the substrate temperature from room temperature (RT) to 500 °C while keeping the metal thickness constant at 10 nm and (c) annealing the RT Ti sputtered NRs at temperatures of 400 °C and 500 °C. The photoluminescence (PL) spectra show that the near band edge luminescence of ZnO in the ultraviolet (UV) region is enhanced as the thickness of Ti increases up to 5 nm and, thereafter, it falls. Sputtering of Ti on ZnO NRs at RT does not cause any UV enhancement but when sputtered at and above 400 °C, the UV intensity is enhanced. Annealing of RT Ti sputtered NRs at and above 400 °C also results in the enhancement of the UV peak, although with a lesser magnitude. Analysis of the PL results, supported by X-ray diffraction, field emission scanning electron microscopy, elemental mapping, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy and electrical I–V measurement results, show a clear indication that the surface diffusion of Ti causes a reduction in the surface defects.

An activated-carbon (AC) assisted route is developed to synthesize a ZnO nanoparticle network. The route involves simple addition of AC to the solution containing the zinc salt and finally removing them by burning at higher temperature to form a sponge-like porous ZnO nanoparticles. The surface area measurements show that AC-assisted ZnO nanoparticles (AC-ZnO) have a higher surface area than those synthesized without AC (B-ZnO), which is further confirmed by the field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM) images. Ultraviolet (UV) absorbance results show that the optical quality remains almost unchanged for both types of nanoparticles. Enhanced and faster UV photosensitivity has been observed for the AC-ZnO. The change in the UV photosensing properties demonstrated here provides a new approach to synthesizing other high surface area materials for novel physical and chemical properties.

Core-shell TiO(2)@ZnO nanorods (NRs) have been fabricated by a simple two step method: growth of ZnO NRs' array by an aqueous chemical technique and then coating of the NRs with a solution of titanium isopropoxide [Ti(OC(3)H(7))(4)] followed by a heating step to form the shell. The core-shell nanocomposites are composed of single-crystalline ZnO NRs, coated with a thin TiO(2) shell layer obtained by varying the number of coatings (one, three and five times). The ultraviolet (UV) emission intensity of the nanocomposite is largely quenched due to an efficient electron-hole separation reducing the band-to-band recombinations. The UV photoconductivity of the core-shell structure with three times TiO(2) coating has been largely enhanced due to photoelectron transfer between the core and the shell. The UV photosensitivity of the nanocomposite becomes four times larger while the photocurrent decay during steady UV illumination has been decreased almost by 7 times compared to the as-grown ZnO NRs indicating high efficiency of these core-shell structures as UV sensors.

Dispersion of ZnO quantum dots in SiO2 matrix has been achieved in two techniques based on StOber method to form ZnO QDs‐SiO2 nanocomposites. Sample A is formed with random dispersion by adding tetraethyl orthosilicate (TEOS) to an ethanolic solution of ZnO nanoparticles and sample B is formed with a chain‐like ordered dispersion by adding ZnO nanoparticles to an already hydrolyzed ethanolic TEOS solution. The photoluminescence spectra of the as‐grown nanocomposites show strong emission in the ultraviolet region. When annealed at higher temperature, depending on the sample type, these show strong red or white emission. Interestingly, when the excitation is removed, the orderly dispersed ZnO QDs‐SiO2 composite shows a very bright blue fluorescence visible by naked eyes for few seconds indicating their promise for display applications.

Highly efficient ultraviolet (UV) photodetection has been realized in nanocolumnar radio frequency (RF) sputtered ZnO thin films as compared to sol-gel nanocrystalline films and aqueous chemically grown nanowire (NW) arrays. The photo-to-dark current ratio in the columnar films reaches a value as high as 10(6) which is at least 2-4 orders of magnitude higher than that of the sol-gel films and NWs. Such a high value is attributed to a dense compact columnar morphology of the sputtered films with higher surface-related trap states. Within 2 s of UV illumination, five orders of change in the photocurrent have occurred in the sputtered film in contrast to three orders of change in the NWs. The photocurrent decay under steady UV illumination in the sputtered films is only 23%, compared to 50% in the NWs. However, the fall in current under the UV 'off' condition in the sputtered film takes a longer time than in the NWs. These changes are correlated to the deep defect levels of the nanocolumnar films.

Quantum dots (QDs) of ZnO of 2-4 nm size have been encapsulated within a SiO(2) matrix using aqueous chemically grown ZnO nanoparticles in a precursor of tetraethyl orthosilicate. The microstructure shows almost a uniform embedment of the QDs in the SiO(2) matrix, resulting in a ZnO QDs-SiO(2) composite structure. The photocurrent transients of the composite show an instant fall in the current followed by an exponential decay under ultraviolet (UV) illumination, causing negative photoconductivity (NPC), in contrast to the positive photoconductivity in only ZnO nanoparticles. The interface defect states due to the presence of the SiO(2) network around ZnO act as charge trap centers for the photoexcited electrons and are responsible for the NPC. The presence of interface-trapped charges under UV illumination has been further confirmed from capacitance-voltage measurements.

The effect of surface capping with poly(vinyl alcohol) (PVA) on the photocarrier relaxation of the aqueous chemically grown ZnO nanowires (NWs) has been investigated. The decay in the photocurrent during steady ultraviolet illumination due to the photocarrier relaxation has been reduced in the capped NWs, as evidenced from a decrease in the photocurrent only by 12% of its maximum value under steady illumination for 15 min and a decrease in the photocurrent by 49% of its maximum value during the same interval of time in the as-grown NWs. The surface modification is confirmed from the FESEM, HRTEM, and FTIR results. The photoluminescence spectrum shows an enhanced ultraviolet emission and a reduced defect-related emission in the capped ZnO NWs compared to bare ZnO.

ZnO nanowires (NWs) with a ZnS coating are synthesized in order to modify the surface without changing the diameter of the NWs. They have the wurtzite ZnO at the core and a cubic ZnS at the outer layer. The NWs show a sharp ultraviolet and a broad visible emission of the photoluminescence spectra. Surface modification has led to a change in the position of the maxima of the visible emission in ZnO-ZnS NWs. The photocarrier relaxation under steady UV illumination occurs in ZnO NW arrays but is absent in ZnO-ZnS NW arrays. The dark current value for both type of NWs are similar, whereas the photocurrent value is much higher in the surface-modified NWs. Higher photocurrent value indicates a transport of the photogenerated carriers from the ZnS layer to ZnO during UV illumination. The carrier transport mechanism is proposed through a model.

We report the controlled growth of ZnO quantum dots (QDs) on the sidewalls of multiwalled carbon nanotubes (MWCNTs) by a one-step process and study the effect on the photoluminescence (PL) properties of the ZnO QDs-MWCNT composite. The PL intensity of the composite is quenched and the lifetime is reduced compared to the only ZnO QDs. The origin of the PL quenching is discussed in terms of energy transfer, which is examined by varying the density and size of ZnO QDs by changing the molar concentration of the precursor solution for ZnO and the amount of MWCNT.

Photoluminescence spectra of GaN grown by metalorganic chemical-vapor deposition on sapphire show that by reactive ion etching, the intensity of the yellow luminescence (YL) band decreases compared to that of the as-grown GaN, due to nonradiative recombination at the damage-induced defect centers. The intensity of the YL in dry-etched GaN has been found to be dependent on rf power and postetch annealing. No change in intensity is observed with further etching indicating a uniform spread of yellow emitters in the epilayer which supports the view that point defects like VGa are the origin of the YL.

Surface-adsorbed species play an important role in the photophysical properties of one-dimensional (1D) ZnO providing a scope to comprehend the change in these properties with growth techniques as well as parameters. We have shown an unprecedented change in the photoluminescence properties of aqueous chemically grown (ACG) ZnO nanorods (NRs) by positioning the substrate at different precursor column heights by exploiting a simple phenomenon of different amounts of dissolved O2 along the depth of a precursor solution with its surface exposed to air. As anticipated, the NRs grown at the bottom of the reaction vessel show more OH-related defects and/or adsorbed O2 than those grown nearer to the liquid–air interface, resulting in better crystalline quality, ultraviolet (UV)/visible (Vis) photoluminescence intensity and UV photocurrent properties in the latter. Therefore, one can easily tune the photophysical properties of similar 1D oxide NRs simply by varying the substrate position in a columnar reaction vessel used in aqueous chemical growth.