Schottky barrier diode fabrication on n-GaN for altraviolet detection

There are many potential areas for the utilization of GaN-based nitride materials, including ultraviolet photodetectors. Ultraviolet photodetectors are used in the military for missile plume detection and space communications. Medically, ultraviolet photodiodes are used in monitoring skin cancer. Schottky barrier metal-semiconductor contacts are choice devices for the manufacture of ultraviolet photodiodes due to higher short wavelength sensitivity and fast response. They also require simple fabrication technology; suffer lower breakdown voltages, and record larger leakage currents at lower voltages as compared to p-n structures of the same semiconductor material. Thus the formation of a Schottky contact with high barrier height, low leakage current, and good thermal stability in order to withstand high temperature processing and operation are some of the most important factors in improving the performance of Schottky barrier photodiodes to be used for ultraviolet detection. The first stage of this study was to establish a chemical cleaning and etching technique. It was found that KOH was suitable in reducing C from the surface and that (NH4)2S further reduced the surface oxides. The next phase of the work was to select a metal that will allow UV light to pass through at a high transmission percentage: a combination of annealed Ni/Au was found to be ideal. The transmission percentage of this alloy was found to be above 80%. The next phase was the fabrication of Ni/Au Schottky barrier diodes on GaN to study the electrical characteristics of the diodes. Electrical characterization of the diodes showed that the dominant current transport mechanism was thermionic emission, masked by the effects of series resistance, which resulted from the condition of the GaN surface. Finally, we fabricated GaN UV photodiodes and characterized them in the optoelectronic station designed and produced during this research. Device responsivity as high as 31.8 mA/W for GaN and 3.8 mA/W for AlGaN were recorded. The calculated quantum efficiencies of the photodiodes were 11 % for GaN and 1.7 % for AlGaN respectively.Thesis (PhD)--University of Pretoria, 2010.Physicsunrestricte

Progress thus far : women in physics in South Africa

Physics still has a long way to go in addressing acceleration of women to higher ranks of research and leadership. The general trend shows that the personal choices affect the acceleration of women to the top in both research and academia. My reference is on women who already obtained PhDs and are in positions in South Africa. Women in academia has a higher workload than men and women in research centers has a support issue. Figure 1 is a presentation of institutions that offers a full course in Physics, indicating the status of women with a PhD degree in South Africa. It is clear that in the past 12 years - since the launch of women in physics in South Africa (WiPiSA), there has been very little progress in accelerating women to the top. Amongst those listed, there is one HOD, 2 associate professors and 2 full professors. A very interesting information is the profile of a woman whose dad is a physicist, raised six children and have a son as a physicist. Personal journeys of women in physics in South Africa will be found in a later full paper on this topic, to be submitted elsewhere.https://aip.scitation.org/journal/apc2020-06-03am2019Physic

Heterojunction of nanostructured α-Fe2O3/CuO for enhancement of photoelectrochemical water splitting

Please read abstract in the article.The National Research Foundation; the World Academy of Sciences (NRF-TWAS); South African Research Chairs Initiative (SARCHI); the University of Pretoria and the CSIR National Laser Centre Rental Pool Programme.https://www.elsevier.com/locate/jalcomhj2022ChemistryPhysic

Polyaniline nanoparticles for the selective recognition of aldrin : synthesis, characterization, and adsorption

We report the preparation, characterization, and property evaluation of molecularly imprinted polyaniline nanoparticles that can be used for the selective recognition of aldrin. The molecularly imprinted polyaniline nanoparticles were prepared by inverted emulsion polymerization using aldrin as a template and aniline as a functional monomer. The prepared nanoparticles were characterized using UV–vis spectroscopy, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The spectral data confirmed that aldrin was successfully incorporated into the polymer matrix. Atomic force microscopy and scanning electron microscopy analyses revealed that the prepared nanoparticles were spherical in nature with sizes ranging from 60 to 100 nm for nonimprinted particles and from 500 to 1500 nm for imprinted particles. The surface morphology changed from smooth to rough upon the incorporation of aldrin molecules. The electrical properties were evaluated using a four-point probe coupled to a source meter. The nonimprinted nanoparticles showed an electrical conductivity of 4.149 S/cm, which was reduced to 0.546 S/cm in molecularly imprinted polyaniline. The equilibrium dissociation constant and free equilibrium concentration were found to be 0.6 and 0.799 ng/μL, respectively. The adsorption characteristics of aldrin and dichlorodiphenyltrichloroethane (DDT) were investigated to determine the selectivity of the imprinted nanoparticles. The distribution coefficients for DDT and aldrin were 0.76 ng/ng and 1.31 μL/ng, respectively, indicating that the imprinted nanoparticles had a stronger affinity for aldrin than for DDT.The International Programme in Chemical Sciences (IPICS), Uppsala University, Sweden.https://www.elsevier.com/locate/synmet2018-11-01hj2018Physic

Effects of L-arginine concentration on hematite nanostructures synthesized by spray pyrolysis and chemical bath deposition

Please read abstract in the article.The Department of Physics, University of Pretoria for support, the African Laser Centre (ALC, J.S.N.) and the National Research Foundation (NRF) grant No. N0115/115463 (SARChI, M.D.), NRF grant no. N00500/110983 (T.P.J.K.) and a grant from the Photonics Initiative of South Africa.http://www.elsevier.com/locate/physb2021-03-15hj2020Physic

Properties of ITO thin films rapid thermally annealed in different exposures of nitrogen gas

Indium tin oxide (ITO) thin films were rapid thermal annealed (RTA) for 5 min at a temperature of 550 °C in different exposures of nitrogen gas. Effects of these exposures on the structural, morphological, electrical, and optical properties of these films were investigated using X-ray diffraction, atomic force microscopy and field emission-scanning electron microscopy, four-point probe and hall effect measurements, and ultraviolet–visible-near-infrared (UV–VIS–NIR) spectrophotometer, respectively. The un-exposed RTA ITO films maintained (400) plane preferential orientation similar to the un-annealed sample. However, this plane preferential orientation was reduced relative to (222) plane for exposed RTA sample. The grains and surface roughness parameters were reduced for exposed and enhanced for un-exposed RTA samples as compared to the un-annealed sample. Relatively higher electrical conductivity, average solar transmittance, and bandgap values were observed for ITO films annealed while exposed to nitrogen gas. The exposed RTA ITO films showed sheet resistance of 7.91 Ω sq−1, average solar transmittance of 83%, and bandgap of 3.93 eV. Findings from this study suggest that RTA exposure have the potential to control ITO thin films properties, hence, extending its potential applications.Mkwawa University College of Education (a constituent college of the University of Dar es Salaam); International Science Program (ISP) and University of Pretoria.https://link.springer.com/journal/108542021-08-17hj2020Physic

Temperature-dependent current-voltage characteristics of Pd/ZnO Schottky barrier diodes and the determination of the Richardson constant

We report on a systematic investigation of temperature dependent current-voltage (I-V) characteristics of Pd/ZnO Schottky barrier diodes in the 30-300 K temperature range. The ideality factor was observed to decrease with increase in temperature, whilst the barrier height increases with increase in temperature. The observed trend has been attributed to barrier inhomogeneities, which results in a distribution of barrier heights at the interface. Using the dependence of saturation current values on temperature, we have calculated the Richardson constant (A*) which was investigated in the two distinct temperature regions: 140–200 K and 210–300 K and values 3 x10-12 of and 3x10-9 A cm-2 K-2 were obtained, respectively. A mean barrier height of 0.97 eV was obtained in the 140-300 K temperature range. Applying the barrier height inhomogeneities correction, the value of A* was obtained from the modified Richardson plots as 39.43 and 39.03 A cm-2 K-2 in the 140-200 K and 210-300 K temperature range. The modified Richardson constant (A**) has proved to be strongly affected by barrier inhomogeneities and dependent on contact quality.South African National Research Foundation (NRF) and the University of Pretoria.http://www.elsevier.com/locate/mssp2016-06-30hb201

Structural, morphological, optical and electrical properties of Schottky diodes based on CBD deposited ZnO : Cu nanorods

Undoped and copper doped zinc oxide (ZnO) nanorods have been synthesized by a simple chemical bath deposition (CBD) method at a temperature of 90 C. Structural, morphological, optical and electrical properties of the synthesized ZnO nanorods were found to be dependent on the Cu doping percentage. X-ray diffraction (XRD) patterns revealed strong diffraction peaks of hexagonal wurtzite of ZnO, and no impurity phases from metallic zinc or copper. Scanning electron microscopy (SEM) images showed changes in diameter and shape of nanorods, where by those doped with 2 at.% and 3 at.% aggregated and became compact. Selected area electron diffraction (SAED) patterns indicates high quality, single crystalline wurtzite structure ZnO and intensities of bright spots varied with copper doping concentration. UVevisible absorption peaks of ZnO red shifted with increasing copper doping concentration. Raman studies demonstrated among others, strong and sharp E2 (low) and E2 (high) optical phonon peaks confirming crystal structure of ZnO. Current-voltage measurements based on the gold/ZnO nanorods/ITO showed good rectifying behavior of the Schottky diode. The predicted Schottky barrier height of 0.60 eV was obtained which is not far from the theoretical Schottky-Mott value of 0.80 eVThe University of Pretoria and National Research Foundation (NRF), South Africa, Grant No: 91550 and 94166.http:// www.elsevier.com/locate/superlattices2018-07-31hb2017Physic

Electrically enhanced transition metal dichalcogenides as charge transport layers in metallophthalocyanine-based solar cells

Transitional metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2) have found application in photovoltaic cells as a charge transporting layer due to their high carrier mobility, chemical stability, and flexibility. In this research, a photovoltaic device was fabricated consisting of copper phthalocyanine (CuPc) as the active layer, exfoliated and Au-doped MoS2, which are n-type and p-type as electron and hole transport layers, respectively. XRD studies showed prominent peaks at (002) and other weak reflections at (100), (103), (006), and (105) planes corresponding to those of bulky MoS2. The only maintained reflection at (002) was weakened for the exfoliated MoS2 compared to the bulk, which confirmed that the material was highly exfoliated. Additional peaks at (111) and (200) planes were observed for the Au doped MoS2. The interlayer spacing (d002) was calculated to be 0.62 nm for the trigonal prismatic MoS2 with the space group P6m2. Raman spectroscopy showed that the E1 2 g (393 cm−1 ) and A1g (409 cm−1 ) peaks for exfoliated MoS2 are closer to each other compared to their bulk counterparts (378 and 408 cm−1 , respectively) hence confirming exfoliation. Raman spectroscopy also confirmed doping of MoS2 by Au as the Au-S peak was observed at 320 cm−1 . Exfoliation was further confirmed by SEM as when moving from bulky to exfoliated MoS2, a single nanosheet was observed. Doping was further proven by EDS, which detected Au in the sample suggesting the yield of a p-type Au-MoS2. The fabricated device had the architecture: Glass/FTO/Au-MoS2/CuPc/MoS2/Au. A quadratic relationship between I-V was observed suggesting little rectification from the device. Illuminated I-V characterization verified that the device was sensitive and absorbed visible light. Upon illumination, the device was able to absorb photons to create electron-hole pairs and it was evident that semipermeable junctions were formed between Au-MoS2/CuPc and CuPc/MoS2 as holes and electrons were extracted and separated at respective junctions generating current from light. This study indicates that the exfoliated and Au-MoS2 could be employed as an electron transporting layer (ETL) and hole transporting layer (HTL), respectively in fabricating photovoltaic devices.The National Research Foundation (NRF), South Africahttp://frontiersin.org/Chemistrypm2021ChemistryPhysic

Electrical characterisation of electron beam exposure induced defects in silicon

The defects introduced in epitaxially grown p-type silicon (Si) during electron beam exposure were electrically characterised using deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS. In this process, Si samples were first exposed to the conditions of electron beam deposition (EBD) without metal deposition. This is called electron beam exposure (EBE) herein. After 50 minutes of EBE, nickel (Ni) Schottky contacts were fabricated using the resistive deposition method. The defect level observed using the Ni contacts had an activation energy of H(0.55). This defect has an activation energy similar to that of the I-defect. The defect level is similar to that of the HB4, a boron related defect. DLTS depth profiling revealed that H(0.55) could be detected up to a depth of 0.8 μm below the junction. We found that exposing the samples to EBD conditions without metal deposition introduced a defect which was not introduced by the EBD method. We also observed that the damage caused by EBE extended deeper into the material compared to that caused by EBD.National Research Foundation of South Africa.http://www.elsevier.com/locate/physb2017-01-31hb2016Physic