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

Electrical characterization of 5.4 MeV alpha-particle irradiated 4H-SiC with low doping density

Nickel Schottky diodes were fabricated on 4H-SiC. The diodes had excellent current rectification with about ten orders of magnitude between 50 V and +2 V. The ideality factor was obtained as 1.05 which signifies the dominance of the thermionic emission process in charge transport across the barrier. Deep level transient spectroscopy revealed the presence of four deep level defects in the 30–350 K temperature range. The diodes were then irradiated with 5.4 MeV alpha particles up to fluence of 2.6 1010 cm 2. Current–voltage and capacitance–voltage measurements revealed degraded diode characteristics after irradiation. DLTS revealed the presence of three more energy levels with activation enthalpies of 0.42 eV, 0.62 eV and 0.76 eV below the conduction band. These levels were however only realized after annealing the irradiated sample at 200 C and they annealed out at 400 C. The defect depth concentration was determined for some of the observed defects.National Research Foundation (NRF) of South Africa.http://www.elsevier.com/locate/nimb2016-09-30hb201

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

Electrical characterization of electron irradiated and annealed lowly-doped 4H-SiC

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

Electrical characterization of high energy electron irradiated Ni/4H-SiC Schottky barrier diodes

The effect of high energy electron (HEE) irradiation on Ni/4H-SiC Schottky barrier diodes was evaluated by current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. Electron irradiation was achieved by using a radioactive strontium source with peak emission energy of 2.3 MeV. Irradiation was performed in fluence steps of 4.9 × 1013 cm–2 until a total fluence of 5.4 × 1014 cm–2 was reached. The Schottky barrier height determined from (I-V) measurements was not significantly changed by irradiation while that obtained from (C-V) measurements increased with irradiation. The ideality factor was obtained before irradiation as 1.05 and this value did not significantly change as a result of irradiation. The series resistance increased from 47 Ω before irradiation to 74 Ω after a total electron fluence of 5.4 × 1014 cm–2. The net donor concentration decreased with increasing irradiation fluence from 4.6 × 1014 cm–3 to 3.0 × 1014 cm–3 from which the carrier removal rate was calculated to be 0.37 cm–1.National Research Foundation (NRF) of South Africahttp://link.springer.com/journal/116642017-08-31hb2016Physic

The influence of high energy electron irradiation on the Schottky barrier height and the Richardson constant of Ni/4H-SiC Schottky diodes

Please read abstract in the article.National Research Foundation (NRF) of South African (Grant specific unique reference number (UID) 78838).http://www.elsevier.com/locate/mssp2016-11-30hb201

Effects of 5.4 MeV alpha-particle irradiation on the electrical properties of nickel Schottky diodes on 4H-SiC

Current–voltage, capacitance–voltage and conventional deep level transient spectroscopy at temperature ranges from 40 to 300 K have been employed to study the influence of alpha-particle irradiation from an 241Am source on Ni/4H–SiC Schottky contacts. The nickel Schottky barrier diodes were resistively evaporated on n-type 4H–SiC samples of doping density of 7.1 1015 cm 3. It was observed that radiation damage caused an increase in ideality factors of the samples from 1.04 to 1.07, an increase in Schottky barrier height from 1.25 to 1.31 eV, an increase in series resistance from 48 to 270 X but a decrease in saturation current density from 55 to 9 10 12Am 2 from I–V plots at 300 K. The free carrier concentration of the sample decreased slightly after irradiation. Conventional DLTS showed peaks due to four deep levels for as-grown and five deep levels after irradiation. The Richardson constant, as determined from a modified Richardson plot assuming a Gaussian distribution of barrier heights for the as-grown and irradiated samples were 133 and 151 A cm 2 K 2, respectively. These values are similar to literature values.National Research Foundation (NRF) of South African (Grant specific unique reference number (UID) 78838).http://www.elsevier.com/locate/nimb2016-12-31hb201

Electrical characterisation of particle irradiated 4H-SiC

Silicon Carbide is a wide bandgap semiconductor with excellent physical and opto-electrical properties. Among these excellent properties are its radiation hardness, high temperature operation and high electric field breakdown. SiC can therefore be used in the fabrication of electronic devices capable of operating in harsh environments, e.g. radiation detectors. Like any other semiconductor, the success of SiC in device fabrication depends on elimination of defects that are detrimental to desired devices or controlled introduction of desired energy levels. The first step in so doing is understanding the defects that are either found in as grown material, introduced during device fabrication or introduced during device operation. In this study nickel ohmic and Schottky contacts were resistively fabricated on n-type 4H-SiC with a net doping density of 4 × 1014 cm-3. Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and Laplace-DLTS measurement techniques were used to electrically characterize the fabricated Schottky diodes. The diodes were then irradiated with low energy electrons, alpha particles and protons. The characterization measurements were repeated after irradiation to evaluate the effect of irradiation on the electrical properties of SiC. It was observed from I-V measurements that electron, alpha particle and proton irradiations do not significantly affect the rectification of Ni/SiC Schottky contacts. C-V measurements indicated that the free carrier removal rate is higher for alpha particle irradiation as compared to electron irradiation. The irradiated diodes were annealed in argon ambient and significant recovery in the free carrier concentration was observed below 600 °C. The free carrier concentration of proton irradiated Schottky contacts, which was decreased to below detection levels was also partly recovered after heat treatment of up to 400 °C. DLTS and Laplace-DLTS measurements revealed the presence of four defect levels in as-grown 4H-SiC. These defects have been labelled E0.10, E0.12, E0.17 and E0.69 where the subscripts indicate the activation energies of the respective defects. Electron, alpha particle and proton irradiations were observed to induce three more defect levels with activation energies of 0.42 eV, 0.62 eV and 0.76 eV. Additionally, these irradiations were also observed to enhance the concentration of level E0.69. All the radiation induced defects were annealed out at temperatures below 600 °C. In proton irradiated diodes, another defect with activation energy of 0.31 eV was observed after annealing the irradiated diodes at 625 °C.Dissertation (MSc)--University of Pretoria, 2014.lk2014PhysicsMScUnrestricte

Use of interfacial layers to prolong hole lifetimes in hematite probed by ultrafast transient absorption spectroscopy

Hematite is a widely investigated material for applications in solar water oxidation due primarily to its small bandgap. However, full realization of the material continues to be hampered by fast electron-hole recombination rates among other weaknesses such as low hole mobility, short hole diffusion length and low conductivity. To address the problem of fast electron-hole recombination, researchers have resorted to growth of nano-structured hematite, doping and use of under-layers. Under-layer materials enhance the photo-current by minimising electron-hole recombination through suppressing of back electron flow from the substrate, such as fluorine-doped tin oxide (FTO), to hematite. We have carried out ultrafast transient absorption spectroscopy on hematite in which Nb2O5 and SnO2 materials were used as interfacial layers to enhance hole lifetimes. The transient absorption data was fit with four different lifetimes ranging from a few hundred femtoseconds to a few nanoseconds. We show that the electron-hole recombination is slower in samples where interfacial layers are used than in pristine hematite. We also develop a model through target analysis to illustrate the effect of under-layers on electron-hole recombination rates in hematite thin films.A.T.P. acknowledges bursaries from the African Laser Centre (ALC) and from the University of Pretoria (UP Postgraduate Research Support Bursary). K.M. acknowledges University of Botswana for financial support. M.D. acknowledges the National Research Foundation (NRF), South Africa, for financial assistance, (National Flagship Programme, Grant number 88021). T.P.J.K. acknowledges the Rental Pool Programme of the National Laser Centre and Department of Science and Technology (Grant number LREJA11), and a grant from the Photonics Initiative of South Africa.http://www.elsevier.com/locate/physb2019-04-15hj2018Physic

Photoelectrochemical performance and ultrafast dynamics of photogenerated electrons and holes in highly titanium-doped hematite

Please read abstract in the article.The African Laser Centre (ALC), the University of Pretoria (UP Postgraduate Research Support Bursary), the University of Botswana, the National Research Foundation (NRF), South Africa, the Swiss-South African joint Research (SSAJR) project, the Rental Pool Programme of the National Laser Centre and Department of Science and Innovation and the Photonics Initiative of South Africa.http://www.rsc.org/journals-books-databases/about-journals/PCCP2021-11-12hj2021Physic