S. Nandy

Current transport mechanism at metal–semiconductor nanoscale interfaces based on ultrahigh density arrays of p-type NiO nano-pillars

The present work focuses on a qualitative analysis of localised I-V characteristics based on the nanostructure morphology of highly dense arrays of p-type NiO nano-pillars (NiO-NPs). Vertically aligned NiO-NPs have been grown on different substrates by using a glancing angle deposition (GLAD) technique. The preferred orientation of as grown NiO-NPs was controlled by the deposition pressure. The NiO-NPs displayed a polar surface with a microscopic dipole moment along the (111) plane (Taskers type III). Consequently, the crystal plane dependent surface electron accumulation layer and the lattice disorder at the grain boundary interface showed a non-uniform current distribution throughout the sample surface, demonstrated by a conducting AFM technique (c-AFM). The variation in I-V for different points in a single current distribution grain (CD-grain) has been attributed to the variation of Schottky barrier height (SBH) at the metal-semiconductor (M-S) interface. Furthermore, we observed that the strain produced during the NiO-NPs growth can modulate the SBH. Inbound strain acts as an external field to influence the local electric field at the M-S interface causing a variation in SBH with the NPs orientation. This paper shows that vertical arrays of NiO-NPs are potential candidates for nanoscale devices because they have a great impact on the local current transport mechanism due to its nanostructure morphology.

Thickness-dependent blue shift in the excitonic peak of conformally grown ZnO:Al on ion-beam fabricated self-organized Si ripples

Al-doped ZnO (AZO) thin films of thicknesses 5,10, 15, 20, and 30 nm were deposited on 500 eV argon ion-beam fabricated nanoscale self-organized rippled-Si substrates at room temperature and are compared with similar films deposited on pristine-Si substrates (without ripples). It is observed that morphology of self-organized AZO films is driven by the underlying substrate morphology. For instance, for pristine-Si substrates, a granular morphology evolves for all AZO films. On the other hand, for rippled-Si substrates, morphologies having chain-like arrangement (anisotropic in nature) are observed up to a thickness of 20 nm, while a granular morphology evolves (isotropic in nature) for 30 nm-thick film. Photoluminescence studies reveal that excitonic peaks corresponding to 5–15 nm-thick AZO films, grown on rippled-Si templates, show a blue shift of 8 nm and 3 nm, respectively, whereas the peak shift is negligible for 20-nm thick film (with respect to their pristine counter parts). The observed blue shifts are substantiated by diffuse reflectance study and attributed to quantum confinement effect, associated with the size of the AZO grains and their spatial arrangements driven by the anisotropic morphology of underlying rippled-Si templates. The present findings will be useful for making tunable AZO-based light-emitting devices.

Tunable optoelectronic properties of pulsed dc sputter-deposited ZnO:Al thin films: Role of growth angle

In this paper, we investigate the role of deposition angle on the physical properties and work function of pulsed dc sputter-deposited Al-doped zinc oxide (AZO) thin films. It is observed that average grain size and crystal quality increase with higher angle of deposition, yielding improved optical properties. A systematic blue shift as well as a decrease in the resistivity takes place with the increasing growth angle up to 70°, while an opposite trend is observed beyond that. In addition, the work function of AZO films is also measured using Kelvin probe force microscopy, which corroborates well with the optical and structural properties. The observed results are explained in the framework of growth angle induced diffusion and shadowing effects. The films deposited at higher angles will be important for rapid incorporation into new technological applications that require a transparent conductive oxide.

Highly conductive grain boundaries in copper oxide thin films

High conductivity in the off-state and low field-effect mobility compared to bulk properties is widely observed in the p-type thin-film transistors of Cu2O, especially when processed at moderate temperature. This work presents results from in situ conductance measurements at thicknesses from sub-nm to around 250 nm with parallel X-ray photoelectron spectroscopy. An enhanced conductivity at low thickness is explained by the occurrence of Cu(II), which is segregated in the grain boundary and locally causes a conductivity similar to CuO, although the surface of the thick film has Cu2O stoichiometry. Since grains grow with an increasing film thickness, the effect of an apparent oxygen excess is most pronounced in vicinity to the substrate interface. Electrical properties of Cu2O grains are at least partially short-circuited by this effect. The study focuses on properties inherent to copper oxide, although interface effects cannot be ruled out. This non-destructive, bottom-up analysis reveals phenomena which are commonly not observable after device fabrication, but clearly dominate electrical properties of polycrystalline thin films.

Stress Induced Mechano-electrical Writing-Reading of Polymer Film Powered by Contact Electrification Mechanism

Mechano-electrical writing and reading in polyaniline (PANI) thin film are demonstrated via metal-polymer contact electrification mechanism (CEM). An innovative conception for a non-destructive self-powered writable-readable data sheet is presented which can pave the way towards new type of stress induced current harvesting devices. A localized forced deformation of the interface has been enacted by pressing the atomic force microscopic probe against the polymer surface, allowing charge transfer between materials interfaces. The process yields a well-defined charge pattern by transmuting mechanical stress in to readable information. The average of output current increment has been influenced from 0.5 nA to 15 nA for the applied force of 2 nN to 14 nN instead of electrical bias. These results underscore the importance of stress-induced current harvesting mechanism and could be scaled up for charge patterning of polymer surface to writable-readable data sheet. Time evolutional current distribution (TECD) study of the stress-induced patterned PANI surface shows the response of readability of the recorded data with time.

Optical and electrical properties of amorphous CuAlO 2 thin film deposited by RF magnetron sputtering

Defects chemistry plays an important role in the origin of p-type conductivity in transparent CuAlO2 thin films. CuAlO2 thin film was deposited at room temperature by RF magnetron sputtering on glass and silicon substrates. Films were deposited with various O2 partial pressures in the Ar+O2 atmosphere. UV-Vis spectrophotometric measurement indicated the films were having transparency above 75% in the visible region and the tauc gap was 1.6 eV. The room temperature electrical conductivity of the film was 0.32 S cm-1.

Optical and electrical properties of amorphous CuAlO2 thin film deposited by RF magnetron sputtering

Defects chemistry plays an important role in the origin of p-type conductivity in transparent CuAlO2 thin films. CuAlO2 thin film was deposited at room temperature by RF magnetron sputtering on glass and silicon substrates. Films were deposited with various O2 partial pressures in the Ar+O2 atmosphere. UV-Vis spectrophotometric measurement indicated the films were having transparency above 75% in the visible region and the tauc gap was 1.6 eV. The room temperature electrical conductivity of the film was 0.32 S cm-1.