Growth, Optical Characterization and Modelling of ZnO Nanorods on Si, SiC and Macroporous Si Structure (original) (raw)
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Growth, Optical Characterization and Modeling of ZnO Nanorods on Si, SiC Microporous Si Structures
2009
Zinc Oxide (ZnO) and Silicon Carbide (SiC) are prominent materials with large applicability such as optoelectronic nanodevices and for instance ultraviolet detectors. There is lack of important information about optical transitions beyond the indirect band gap energy (BGE) of 4H-SiC and even more for ZnO direct BGE grown on the former material. Using vapor-liquid-solid and the aqueous chemical growth methods we have grown ZnO nanorods on different substrates, such as quartz, n-and ptype porous silicon, and n-type 4H-SiC. Scanning electron microscopy (SEM) was employed to compare sample morphologies. The absorption was calculated employing a projector augmented wave (PAW) method. The measured absorption of ZnO nanorods, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the low energy spectral range. It is observed a strong effect of 4H-SiC substrates on ZnO nanorod properties. Experiment and theory show a good agreement when the shape of the optical absorption is considered for both materials.
Optical Properties and Field Emission of ZnO Nanorods Grown on p-Type Porous Si
N-type ZnO nanorods were grown on p-type porous silicon using a chemical bath deposition (CBD) method (p-n diode). The structure and geometry of the device were examined by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) while the optoelectronic properties were investigated by UV/Vis absorption spectrometry as well as photoluminescence and electroluminescence measurements. The field emission (FE) properties of the device were also measured and its turn-on field and current at 6 V/µm were determined. In principle, the growth of ZnO nanorods on porous siicon for optoelectronic applications is possible.
Study of luminescent centers in ZnO nanorods catalytically grown on 4H-p-SiC
Semiconductor Science and Technology, 2009
High quality ZnO nanorods (NRs) were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates. Heterojunction light emitting diodes (LEDs) were fabricated. Electrical characterisation including deep level transient spectroscopy (DLTS) complemented by photolumincence (PL) are used to characterize the heterojunction LEDs. On contrary to previously published results on n-ZnO thin films on p-SiC, we found that the dominant emission is originating from the ZnO NRs. Three luminescence lines have been observed, these are associated with blue (465 nm) and violet (446 nm) emission lines from ZnO NRs emitted by direct transition/recombination of carriers from the conduction band to a zinc vacancy (V Zn ) radiative centre and from zinc interstitial (Zn i ) radiative center to the valance band. The third green-yellow (575 nm) spectral line is emitted due to a transition of carriers from Zn i to V Zn . The superposition of these lines led to the observation of strong white light which appears as a wide band in the room temperature PL.
Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC
Journal of Luminescence, 2010
Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4Hp-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors.
ELECTRICAL PROPERTIES OF NANOROD-BASED ZnO/SiC HYBRID HETEROJUNCTIONS
NANOCON 2019 Conference Proeedings, 2020
ZnO nanorods have attracted increasing interest in recent years due to their potential in optoelectronic applications. The lack of p-type ZnO emphasizes the importance of rectifying junctions realized on other ptype materials. SiC is a good candidate to create hybrid heterojunctions with ZnO due to its wurtzite crystal structure and a small lattice and thermal mismatch. The ZnO/SiC heterojunctions have a potential to show intense UV electroluminescence. We investigate morphology and electrical properties of a single verticallyoriented ZnO nanorod on a SiC substrate. The current-voltage measurements are performed directly in the vacuum chamber of a scanning electron microscope. The contact to a single nanorod is obtained by a nanoprobe, which allows for the measurement of the current-voltage characteristic of a single nanorod heterojunction of choice. The influence of ZnO growth parameters and post-growth treatment of ZnO/SiC structures are studied with the aim to minimize the density of structural/interfacial defects and to create lowdimensional hybrid heterojunctions with the potential to show intense UV electroluminescence.
Growth of ZnO Nanostructures on Porous Silicon and Oxidized Porous Silicon Substrates
Brazilian Journal of Physics, 2011
We have investigated an oxidation of substrate effect on structural morphology of zinc oxide (ZnO) rods. ZnO rods are grown on porous silicon (PS) and on thermally oxidized porous silicon substrates by carbothermal reduction of ZnO powder through chemical vapour transport and condensation. Porous silicon is fabricated by electrochemical etching of silicon in hydrofluoric acid solution. The effects of substrates on morphology and structure of ZnO nanostructures have been studied. The morphology of substrates is studied by atomic force microscopy in contact mode. The texture coefficient of each sample is calculated from X-ray diffraction data that demonstrate random orientation of ZnO rods on oxidized porous silicon substrate. The morphology of structures is investigated by scanning electron microscopy that confirms the surface roughness tends to increase the growth rate of ZnO rods on oxidized PS compared with porous silicon substrate. A green emission has been observed in ZnO structures grown on oxidized PS substrates by photoluminescence measurements.
Semiconductor Science and Technology, 2014
The electrical and optical properties of heterojunctions formed by thermally deposited ZnO thin films on n-type 4H-SiC substrates have been investigated. Current-voltage characteristics of the fabricated light emitting devices revealed excellent rectifying behaviors with a typical leakage current lower than 1 nA at a reverse bias of −3 V, and with a forward current at 3 V in the range of 2 mA. A study of the electroluminescent characteristics of ZnO/SiC heterojunctions over the temperature range of 50-450 K showed an emission peak around 410 nm and a broad defect-related electroluminescence at room temperature in the visible range for a forward current of 300 mA. Electrically active deep level centers in ZnO and n-type 4H-SiC epilayers have been investigated by deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS (LDLTS). Additionally, LDLTS has successfully been employed to resolve the closely spaced hole trap energy levels.
Heteroepitaxial ZnO nano hexagons on p-type SiC
Journal of Crystal Growth, 2010
ZnO single crystal nanohexagons have been grown heteroepitaxially on p-type Si-face 4H-SiC substrates with 8 o miscut from [0001] by catalyst-free atmospheric pressure metalorganic chemical vapor deposition and characterized by x-ray diffraction, scanning and transmission electron microscopy as well as energy disperse x-ray and cathodoluminescence analyses. The as-grown ZnO nanohexagons have a pillar shape terminated by a and c plane facets, and are aligned along the growth direction with the epitaxial relation [0001] ZnO //[0001] 4H-SiC and [10 1 0] ZnO //[10 1 0] 4H-SiC . The ZnO nanohexagons demonstrate intense UV emission ( NBE = 376 nm) and negligible defect related luminescence.
Journal of Luminescence, 2012
We report on a comparative micro-photoluminescence investigation of ZnO hexagonal nanopillars (HNPs) and the seeding layer grown on the off-axis 4H-SiC substrate. Transmission electron microscope (TEM) results establish that a thin seeding layer continuously covers the terraces of 4H-SiC prior to the growth of ZnO HNPs. Low temperature photoluminescence (LTPL) shows that ZnO HNPs are only dominated by strong donor bound exciton emissions without any deep level emissions. Micro-LTPL mapping demonstrates that this is specific also for the seeding layer. To further understand the recombination mechanisms, time-resolved micro-PL spectra (micro-TRPL) have been collected at 5 K and identical bi-exponential decays have been found on both the HNPs and seeding layer. Temperaturedependent TRPL indicates that the decay time of donor bound exciton is mainly determined by the contributions of non-radiative recombinations. This could be explained by the TEM observation of the non-radiative defects in both the seeding layer and HNPs, like domain boundaries and dislocations, generated at the ZnO/SiC interface due to biaxial strain.