Women in physics in Zimbabwe

This paper reports on the state of women in physics in Zimbabwe since 2002. Three universities have physics departments: the University of Zimbabwe, National University of Science and Technology, and Midlands State University. These institutions are all state owned. A 10-year survey shows a limited female enrollment at the undergraduate level. We report on the challenges faced by women in physics starting from the primary level of education due to culture and custom. Another reason is the lack of resources owing to the economic hardships currently experienced in the country. The authors suggest possible solutions to the current shortage of women in physics and in science in general.https://aip.scitation.org/journal/apc2020-06-03am2019Physic

The fine structure of electron irradiation induced EL2-like defects in n-GaAs

Defects induced by electron irradiation in n-GaAs have been studied using deep level transient spectroscopy (DLTS) and Laplace DLTS (L-DLTS). The E0.83 (EL2) is the only defect observed prior to irradiation. Ru/n-GaAs Schottky diodes were irradiated with high energy electrons from a Sr-90 radionuclide up to a fluence of 2.45 1013 cm 2. The prominent electron irradiation induced defects, E0.04, E0.14, E0.38, and E0.63, were observed together with the metastable E0.17. Using L-DLTS, we observed the fine structure of a broad base EL2-like defect peak. This was found to be made up of the E0.75, E0.83, and E0.85 defects. Our study reveals that high energy electron irradiation increases the concentration of the E0.83 defect and introduces a family of defects with electronic properties similar to those of the EL2.The authors gratefully acknowledge the financial support of the South African National Research Foundation (NRF) and the University of Pretoria.The South African National Research Foundation (NRF) and the University of Pretoria.http://scitation.aip.org/content/aip/journal/japam2016Physic

The effect of high temperatures on the electrical characteristics of Au/n-GaAs Schottky diodes

In this study, the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Au/n-GaAs Schottky diodes have been measured over a wide temperature range, 80–480 K. The diodes were rectifying throughout the range and showed good thermal stability. Room temperature values for the ideality factor, I–V barrier height and C–V barrier height were found to be n =1.10, ϕIVϕIV=0.85 eV and ϕCVϕCV=0.96 eV, respectively. ϕIVϕIV increases and n decreases with an increase in temperature. We investigated the effect of elevated temperatures on the barrier height and ideality factor by measuring the diodes at a high temperature (annealing mode) then immediately afterwards measuring at room temperature (post annealing mode). The measurements indicate I–V characteristics that degrade permanently above 300 K. Permanent changes to the C–V characteristics were observed only above 400 K. We also noted a discrepancy in the C–V barrier height and carrier concentration between 340 and 400 K, which we attribute to the influence of the EL2 defect (positioned 0.83 eV below the conduction band minima) on the free carrier density. Consequently, we were able to fit the ϕCVϕCV versus temperature curve into two regions with temperature coefficients −6.9×10−4 eV/K and −2.2×10−4 eV/K above and below 400 K.The University of Pretoria and the South African National Research Foundation grant#88021.http://www.journals.elsevier.com/physica-b-condensed-matter2017-01-31hb2016Physic

Rare earth interstitial-complexes in Ge : hybrid density functional studies

Please read abstract in the article.The National Research Foundation (NRF) of South Africa [98961]http://www.elsevier.com/locate/nimb2018-10-15hj2017Physic

Rare earth substitutional impurities in germanium : a hybrid density functional theory study

Please read abstract in the article.The National Research Foundation (NRF) of South Africa [(UID) 98961]http://www.elsevier.com/locate/nimb2018-10-15hj2017Physic

Defects in swift heavy ion irradiated n-4H-SiC

Please read abstract in the article.http://www.elsevier.com/locate/nimb2020-12-01hj2020Physic

Defects induced by solid state reactions at the tungsten-silicon carbide interface

Defects introduced by the solid state reactions between tungsten and silicon carbide have been studied using deep level transient spectroscopy (DLTS) and Laplace DLTS. W/4H-SiC Schottky barrier diodes were isochronally annealed in the 100–1100 C temperature range. Phase composition transitions and the associated evolution in the surface morphology were investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM). After annealing at 1100 C, the E0.08, E0.15, E0.23, E0.34, E0.35, E0.61, E0.67, and E0.82 defects were observed. Our study reveals that products of thermal reactions at the interface between tungsten and n-4H-SiC may migrate into the semiconductor, resulting in electrically active defect states in the bandgap.The South African National Research Foundation (NRF) and the University of Pretoria.http://aip.scitation.org/journal/jap2019-01-18am2018Physic

Electrical characterization of defects induced by electron beam exposure in low doped n-GaAs

We have used deep level transient spectroscopy (DLTS) and Laplace DLTS (L-DLTS) to characterize the electrically active point defects introduced in n-type gallium arsenide by electron beam exposure prior to Schottky metallization. The GaAs crystals were exposed to incident electrons at sub-threshold energies which are deemed low and insufficient to form defects through ion solid interactions. DLTS revealed a set of electron traps different from those commonly observed in n-GaAs after particle irradiation. These different signatures from the same radiation type suggest that different mechanisms are responsible for defect formation in the two electron irradiation processes. An analysis of the conditions under which the defects were formed was done to distil a number of possible defect formation mechanisms using the experimental evidence obtained.The South African National Research Foundation (NRF) and the University of Pretoria.http://www.elsevier.com/locate/nimb2018-10-30Physic

The effects of high-energy proton irradiation on the electrical characteristics of Au/Ni/4H-SiC Schottky barrier diodes

Please read abstract in the article.The University of Pretoria and the National Research Foundation (NRF) of South Africa, Grant number 98961.http://www.elsevier.com/locate/nimb2018-10-15hj2017Physic

Electrical characterization of process and irradiation induced defects in GaAs

Gallium arsenide (GaAs) technology leads the implementation of high frequency devices with superior performance. A vast number of optoelectronic applications are based on the material owing to its direct and wide bandgap. Over the years the number of these applications continues to grow but they remain highly cost-ineffective partly due to the growth techniques and the presence of defects in GaAs. These areas have been researched on intensively over the past four decades with much controversy, particularly on the subject of the EL2 defect. This defect plays an important role in the design and operation of GaAs based devices. It is therefore important to understand its electronic properties and influence on device operation. Schottky barrier diodes (SBDs) were fabricated on n-type GaAs. The quality of the contacts was evaluated using current-voltage (I-V) and capacitance-voltage (C-V) measurements before and after exposing them to different processing techniques and radiation types. Deep-level transient spectroscopy (DLTS) and Laplace deeplevel transient spectroscopy (L-DLTS) were used to characterize the electrically active defects in the material. Defects with almost similar emission rates which were not observed in the past were identified using L-DLTS due to its high resolution. I-V and C-V measurements on as-deposited Au/n-GaAs SBDs in the 80 ?? 480 K range showed that the EL2 defect has a profound effect on the diode characteristics. The influence of the defect caused the temperature dependent behavior of the C-V barrier height to be split into two temperature intervals, each with a unique temperature coefficient. Exposure of the devices to temperatures above 300 K resulted in the deterioration of their I-V characteristics. Permanent physical modification of the SBDs was observed at 400 K and above. Inductively coupled plasma (ICP) etching, Electron beam deposition (EBD) and electron beam exposure (EBE) were observed to impact significantly on diode I-V and C-V characteristics. ICP etching resulted in devices with a lower reverse leakage current and high barrier height whereas EBD fabricated devices exhibited the poorest characteristics. DLTS results revealed that processing introduced electrically active defects in the bandgap. EBE induced defects had different electronic properties to all the processing and radiation induced defects observed in previous studies. I-V and C-V characteristics of SBDs exposed to alpha and beta-particle irradiation were identical to as-deposited samples. This demonstrated the radiation hardness of GaAs. DLTS spectra of alpha-particle irradiated SBDs displayed the defect peaks sitting on a skewed baseline which hampered accurate L-DLTS measurements. In addition to the prominent irradiation induced defects, high energy electron-irradiation was observed to induce defects with electronic properties similar to those of the EL2.Dissertation (MSc)--University of Pretoria, 2016.PhysicsMScUnrestricte