Showing papers on "Substrate (electronics) published in 2022"

Large area van der Waals epitaxy of II–VI CdSe thin films for flexible optoelectronics and full-color imaging

Abstract: The demand for future semiconductor devices with enhanced performance and lower cost has driven the development of epitaxial growth of high quality, free-standing semiconductor thin film materials without the requirement of lattice matching to the substrate, as well as their transfer to other substrates and associated device processing technology. This work presents a study on the van der Waals epitaxy based molecular beam epitaxy of CdSe thin films on two-dimensional layered mica substrates, as well as related etch-free layer transfer technology of large area, free-standing layers and their application in flexible photodetectors for full-color imaging. The photoconductor detectors based on these flexible CdSe thin films demonstrate excellent device performance at room temperature in terms of responsivity (0.2 A·W−1) and detectivity (1.5 × 1012 Jones), leading to excellent full-color imaging quality in the visible spectral range. An etch-free and damage-free layer transfer method has been developed for transferring these CdSe thin films from mica to other substrate for further device processing and integration. These results demonstrate the feasibility of van der Waals epitaxy method for growing high quality, large area, and free-standing epitaxial layers without the requirement for lattice matching to substrate for applications in low-cost flexible and/or monolithic integrated optoelectronic devices.

The effect of ultrasonic wave amplitude on the physical properties of zinc oxide (ZnO) deposited by ultrasonic spray method

Abstract: In this study, high quality zinc oxide (ZnO) thin films, with improved properties, were prepared by a cost-effective ultrasonic spray pyrolysis technique via a careful optimization of the used ultrasonic wave amplitude. The deposition process was performed on glass substrate and were subsequently annealed at 400 °C. We investigated the effect of various ultrasonic wave amplitude on the structural, surface morphology, optical and electrical properties of the obtained thin films, after varying the applied wave amplitude. Furthermore, deposited thin films were studied by means of XRD, UV–vis spectrophotometer, scanning electron microscope, and four-point probe technique. XRD analysis confirmed that obtained ZnO thin films have polycrystalline structure and a wurtzite (hexagonal) phase, with a c-axis preferred orientation (0 0 2). The crystallite size was about 23–30 nm. The SEM micrographs of the surface morphology show uniform, homogenous and dense films with granular structures. The films thicknesses were found to be dependent on the used wave amplitude; they were ranged from 184 to 423.5 nm. In addition, the optical properties of the deposited thin films reveal that the films are highly transparent in the visible region above 80%, while the value of energy band gap varies from 3.24 to 3.27 eV. The Electrical properties investigation revealed a resistivity around 10-3 Ω.cm, showing also a non negligible dependency with the wave amplitude tuning. We obtained an improvement in the carrier concentration (1.6 × 1020–3.9 × 1020 cm−3) and mobility (4.2–15 cm2/V.s) with the ultrasonic wave amplitude rising. High quality ZnO thin films with enhanced properties are in demand and have a large wide of applications in optoelectronics and solar cells.

Origin of the Diffusion-Related Optical Degradation of 1.3 μm Inas QD-LDs Epitaxially Grown on Silicon Substrate

Abstract: This paper investigates the origin of the diffusion process responsible for the optical degradation of InAs quantum dot (QD) laser diodes epitaxially grown on silicon. By means of a series of constant-current stress experiments carried out at different temperatures, we were able to quantitatively evaluate the temperature acceleration of the degradation process. In addition, the presence of temperature thresholds above which the degradation rate drastically increases was ascribed to the onset of a recombination-enhanced degradation process, which is favored at high temperatures. Finally, the comparison of the experimentally determined diffusion coefficients with prior scientific reports suggests that degradation is related to the recombination-enhanced diffusion of Be, used here as p-type dopant, or of the lattice defects limiting Be diffusion. The original results of this work provide new insight on the microscopic origin of the gradual optical degradation of quantum-dot lasers, which will find wide application in silicon photonics.

Effect of growth parameters on defect structure and optical properties of ultrathin SnO2 films

Abstract: Tin oxide films with thicknesses in the range from 5 to 110 nm have been deposited by reactive dc magnetron sputtering of Sn in Ar + O plasma at a low working pressure of 1.0× 10 −3 Torr on glass substrates at different temperatures (150–400 °C). The effect of deposition time, substrate temperature, and oxygen partial pressure on surface morphology , crystallographic structure, optical properties, and photoluminescence characteristics of SnO 2 films has been studied and correlated with their defect structure . The structural transformation from nanocrystalline to polycrystalline of thicker films >40 nm and films were grown at higher temperature is explained based on adatom mobility and uniform substrate coverage. Based on photoluminescence characteristics and transmittance spectra, the 20 nm thick film exhibits the least defect structure and best electronic and optical behaviors.

Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling.

Abstract: We present a 'top-down' patterning technique based on ion milling performed at low-temperature, for the realization of oxide two-dimensional electron system devices with dimensions down to 160 nm. Using electrical transport and scanning Superconducting QUantum Interference Device measurements we demonstrate that the low-temperature ion milling process does not damage the 2DES properties nor creates oxygen vacancies-related conducting paths in the STO substrate. As opposed to other procedures used to realize oxide 2DES devices, the one we propose gives lateral access to the 2DES along the in-plane directions, finally opening the way to coupling with other materials, including superconductors.

Fabrication of junction-free Cu nanowire networks via Ru-catalyzed electroless deposition and their application to transparent conducting electrodes.

Abstract: Over the past few years, metal nanowire networks have attracted attention as an alternative to transparent conducting oxide materials such as indium tin oxide for transparent conducting electrode applications. Recently, electrodeposition of metal on nanoscale template is widely used for formation of metal network. In the present work, junctionless Cu nanowire networks were simply fabricated on a substrate by forming a nanostructured Ru with 80 nm width as a seed layer, followed by direct electroless deposition of Cu. By controlling the density of Ru nanowires or the electroless deposition time, we readily achieve desired transmittance and sheet resistance values ranging from ∼1 kΩ sq-1at 99% to 9 Ω sq-1at 89%. After being transferred to flexible substrates, the nanowire networks exhibited no obvious increase in resistance during 8000 cycles of a bending test to a radius of 2.5 mm. The durability was verified by evaluation of its heating performance. The maximum temperature was greater than 180 °C at 3 V and remained constant after three repeated cycles and for 10 min. Transmission electron microscopy and x-ray diffraction studies revealed that the adhesion between the electrolessly deposited Cu and the seed Ru nanowires strongly influenced the durability of the core-shell structured nanowire-based heaters.

Highly enhanced field emission from vertically aligned carbon nanotubes grown on a patterned substrate via non-lithographic method

Abstract: In the present work, a silicon substrate has been patterned with a gold thin film of thickness 15 nm using thermal evaporation , followed by growth of carbon nanotubes (CNTs) using thermal chemical vapor deposition . The effect of temperature on the growth of CNTs on Au patterned substrate is studied using Raman and Field emission scanning electron microscope (SEM). A significant change in the growth of the CNTs grown on Au film patterned substrate with temperature can be observed using SEM images. However, no significant change in the micro crystallinity of the films was observed. Field emission properties of vertically aligned carbon nanotubes, grown at different temperatures, on gold film patterned substrate has been investigated. For the non-patterned substrate, for the CNT film grown at 900 °C, the current density comes out to be 8.0 mA/cm 2@ 4.8V/μm, which increases to 14.6 mA/cm2 in the case of CNT film grown on gold patterned substrate. The observed enhancement of nearly 180% in current density for the patterned substrate as compared to non-patterned silicon substrate is primarily attributed to the reduced electric field screening. The reduced screening is realized with the help of COMSOL simulation, showing a significant enhancement in the local electric field near edges.