Preliminary Investigation Into The Benefits From Investments In Environmental Research: Case Studies on Water Clarity/Quality and The Biological Management of Possums

MoRST is performing an evaluation of the funds invested in environmental research. The two case studies discussed in this paper contribute to the ongoing decision-making about this investment. Substantial funds have been invested in both research programmes identified. Because the main benefits associated with research output are environmental, they are difficult to value monetarily. Preliminary analysis suggests that at a discount rate of 6%, annual future benefit flows of $7 -$10 million will justify the water quality/clarity research. The expenditure on possum biocontrol will be justified if the research generates an annual future benefit flow of $20 million.Cost benefit analysis, returns to research, environmental research, Community/Rural/Urban Development, Environmental Economics and Policy, Land Economics/Use, Resource /Energy Economics and Policy,

Electronic properties of shallow level defects in ZnO grown by pulsed laser deposition

We have used deep level transient spectroscopy (DLTS) to characterise four defects with shallow levels in ZnO grown by pulsed laser deposition (PLD). These defects all have DLTS peaks below 100 K. From DLTS measurements and Arrhenius plots we have calculated the energy levels of these defects as 31 meV, 64 meV, 100 meV and 140 meV, respectively, below the conduction band. The 100 meV defect displayed metastable behaviour: Annealing under reverse bias at temperatures of above 130 K introduced it while annealing under zero bias above 110 K removed it. The 64 meV and 140 meV defects exhibited a strong electric field assisted emission, indicating that they may be donors

Introduction and annealing of primary defects in proton-bombarded n-GaN

We report on in situ space charge spectroscopy measure-ments on low-temperature 1.6 MeV proton-bombarded n-type gallium nitride thin film samples. The scope of this study was to investigate the introduction and annealing dynamics of radiation-induced lattice damage. Using optical excitation allowed for the detection of electronic defect states in the entire GaN bandgap and to detect unstable primary defects that would have been invisible in thermal space charge spectroscopic measurements. The introduction of compensating acceptor-like primary defects by the bombardment was observed and manifested as a decrease in the sample capacitance. After the bombardment the concentrations of deep-levels and acceptor states were monitored by deep-level transient spectroscopy and photo-capacitance measurements while the temperature was increased. It was found that annealing and reactions of primary bombardment-induced defects occurs even below room-temperature which might account for the radiation-hardness of GaN.University of Pretoria and the National Research Foundation (NRF).http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-3951hb201

Electronic properties of shallow level defects in ZnO grown by pulsed laser deposition

We have used deep level transient spectroscopy (DLTS) to characterise four defects with shallow levels in ZnO grown by pulsed laser deposition (PLD). These defects all have DLTS peaks below 100 K. From DLTS measurements and Arrhenius plots we have calculated the energy levels of these defects as 31 meV, 64 meV, 100 meV and 140 meV, respectively, below the conduction band. The 100 meV defect displayed metastable behaviour: Annealing under reverse bias at temperatures of above 130 K introduced it while annealing under zero bias above 110 K removed it. The 64 meV and 140 meV defects exhibited a strong electric field assisted emission, indicating that they may be donors

Comparison of two models for phonon assisted tunneling field enhanced emission from defects in Ge measured by DLTS

Deep Level Transient Spectroscopy (DLTS) was used to measure the field enhanced emission rate from a defect introduced in n-type Ge. The defect was introduced through low energy (±80 eV) inductively coupled plasma (ICP) etching using Ar. The defect, named EP0.31, had an energy level 0.31 eV below the conduction band. Models of Pons and Makram-Ebeid (1979) [2] and Ganichev and Prettl (1997) [3], which describe emission due to phonon assisted tunnelling, were fitted to the observed electric field dependence of the emission rate. The model of Pons and Makram-Ebeid fitted the measured emission rate more accurately the Ganichev and Prettl. However the model of Ganichev and Prettl has only two parameters, while the model of Pons and Makram-Ebeid has four. Both models showed a trasition in the dominant emission mechanism from a weak electron-phonon coupling below 152.5 K to a strong electron –phonon coupling above 155 K. After the application of a x2 goodness of fit test, it was determined that the model of Pons and Makram-Ebeid describes the data well, while that of Ganichev and Prettl does not.The South African National Research Foundationhttp://www.elsevier.com/locate/phys

Observation of low-temperature annealing of a primary defect in gallium nitride

Primary defects were introduced into n-type gallium nitride (GaN) thin films by 1.6 MeV-proton bombardment at 20 K. The electronic states of these defects were investigated by means of optical space charge spectroscopy. An until now unreported primary defect, HP1, with an electronic state close to the valence band edge was detected. HP1 can be photo-ionised with photon energies of 3.4 eV. It was found to be stable up to 235 K but anneals quickly at temperatures above 240 K.National Research Foundation (NRF)http://www.elsevier.com/locate/physbhb201

Field dependence of the E1' and M3' electron traps in inductively coupled Ar plasma treated n-Gallium Arsenide

Inductively coupled Ar plasma etching of n-type (Si doped) Gallium Arsenide (GaAs) introduces several electron traps, Ec – 0.04 eV (labelled E10), Ec – 0.19 eV, Ec – 0.31 eV, Ec – 0.53 eV, and Ec – 0.61 eV (behaving like the well documented M3 and labelled M30 in this study), of which the metastable defects Ec – 0.04eV (E10 ), and Ec – 0.07 eV are novel. Furthermore, E10 and M30 exhibit strong field enhanced carrier emission. Double-correlation deep level transient spectroscopy was used to investigate the field dependent emission behaviour of these two defects. It is shown that for both traps, the observed enhanced emission is due to phonon assisted tunnelling. The latter observation is contrary to the literature reports suggesting that enhanced carrier emission for M3 occurs via the Poole-Frenkel mechanism.http://jap.aip.org/nf201

Electrical characterization of deep levels created by bombarding nitrogen-doped 4HSiC with alpha-particle irradiation

Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate the effect of alpha-particle irradiation on the electrical properties of nitrogen-doped 4H-SiC. The samples were bombarded with alpha-particles at room temperature (300 K) using an americium-241 (241Am) radionuclide source. DLTS revealed the presence of four deep levels in the as-grown samples, E0.09, E0.11, E0.16 and E0.65. After irradiation with a fluence of 4.1 × 1010 alpha-particles-cm–2, DLTS measurements indicated the presence of two new deep levels, E0.39 and E0.62 with energy level, EC – 0.39 eV and EC –0.62 eV, with an apparent capture cross sections of 2×10–16 and 2×10–14 cm2, respectively. Furthermore, irradiation with fluence of 8.9×1010 alpha-particles-cm–2 resulted in disappearance of shallow defects due to a lowering of the Fermi level. These defects - minutes. Defects, E0.39 and E0.42 with close emission rates were attributed to silicon or carbon vacancy and could only be separated by using high resolution Laplace-DLTS. The DLTS peaks at EC – (0.55-0.70) eV (known as Z1/Z2) were attributed to an isolated carbon vacancy (VC).This work is based on the research supported in part by the National Research Foundation (NRF) of South African (Grant specific unique reference number (UID) 78838).http://www.elsevier.com/locate/nimb2017-03-31hb2016Physic

Determination of capture barrier energy of the e-center in palladium Schottky barrier diodes of antimony-doped germanium by varying the pulse width

Please read abstract in the article.The National Research Foundation (NRF) of South Africahttp://iopscience.iop.org/journal/2053-1591am2020Physic

Electronic properties and transformation kinetics of two prominent metastable defects introduced in GaAs during sputter deposition of Au Schottky contacts

Please read abstract in the article.The National Research Foundation of South Africahttp://www.elsevier.com/locate/mssp2020-08-15hj2020Physic