M. Diale

Effects of hydrogen, oxygen, and argon annealing on the electrical properties of ZnO and ZnO devices studied by current-voltage, deep level transient spectroscopy, and Laplace DLTS

Effects of annealing ZnO in hydrogen, oxygen, and argon have been investigated using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS) measurements. Current-voltage (IV) measurements indicate a decrease in zero–bias barrier height for all the annealed samples. Conventional DLTS measurements reveal the presence of three prominent peaks in the un-annealed and annealed samples. A new peak with an activation enthalpy of 0.60 eV has been observed in the H2 annealed samples, while an estimated energy level of 0.67 eV has been observed in Ar annealed samples. O2 annealing does not introduce new peaks but causes a decrease in the concentration of the E3 peak and an increase in concentration of the E1 peak. The concentrations of all the intrinsic defects have decreased after H2 and Ar annealing; with Ar annealing giving peaks with the lowest concentrations. The E2 peak anneals out after annealing ZnO in Ar and H2 at 300 °C. From the annealing behaviour of E3, we have attributed to transition metal ...

A study of the T2 defect and the emission properties of the E3 deep level in annealed melt grown ZnO single crystals

We report on the space charge spectroscopy studies performed on thermally treated melt-grown single crystal ZnO. The samples were annealed in different ambients at 700 °C and also in oxygen ambient at different temperatures. A shallow donor with a thermal activation enthalpy of 27 meV was observed in the as-received samples by capacitance-temperature, CT scans. After annealing the samples, an increase in the shallow donor concentrations was observed. For the annealed samples, E27 could not be detected and a new shallow donor with a thermal activation enthalpy of 35 meV was detected. For samples annealed above 650 °C, an increase in acceptor concentration was observed which affected the low temperature capacitance. Deep level transient spectroscopy revealed the presence of five deep level defects, E1, E2, E3, E4, and E5 in the as-received samples. Annealing of the samples at 650 °C removes the E4 and E5 deep level defects, while E2 also anneals-out at temperatures above 800 °C. After annealing at 700 °C, t...

Effects of high temperature annealing on single crystal ZnO and ZnO devices

We have systematically investigated the effects of high-temperature annealing on ZnO and ZnO devices using current voltage, deep level transient spectroscopy (DLTS) and Laplace DLTS measurements. Current–voltage measurements reveal the decrease in the quality of devices fabricated on the annealed samples, with the high-temperature annealed samples yielding devices with low barrier heights and high reverse currents. DLTS results indicate the presence of three prominent defects in the as-received samples. Annealing the ZnO samples at 300 °C, 500 °C, and 600 °C in Ar results in an increase in reverse leakage current of the Schottky contacts and an introduction of a new broad peak. After 700 °C annealing, the broad peak is no longer present, but a new defect with an activation enthalpy of 0.18 eV is observed. Further annealing of the samples in oxygen after Ar annealing causes an increase in intensity of the broad peak. High-resolution Laplace DLTS has been successfully employed to resolve the closely spaced ...

Laplace current deep level transient spectroscopy measurements of defect states in methylammonium lead bromide single crystals

The Israel Ministry of Science’s Tashtiot program.and the NRF Nanotechnology Flagship Program (Project No. 88021).

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

The authors gratefully acknowledge the financial support of the South African National Research Foundation (NRF) and the University of Pretoria.

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.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.

Hydrogen production with holes: what we learn from operando studies

As we become more aware of the limited amount of energy available from traditional sources, we are increasingly turning to solar power as a viable alternative.1, 2 Of the total worldwide energy consumption, 20% is electrical, with an increasing share being produced by photovoltaics. Scientists, engineers, technologists, and investors are now working towards a renewable alternative for the remaining 80%, which is currently obtained from fossil fuels, nuclear fuels, and biomass.3–5 Photoelectrochemical cells (PECs), which use sunlight to convert water into solar-hydrogen fuel, represent one route to achieving a renewable energy source. PECs are based on semiconductor photoelectrodes,6 but their principles of energy conversion and storage are analogous to photosynthesis. The photoelectrodes within PECs are comprised of two electrodes. At least one contains a light absorber (which is applied as a coating on a transparent conducting oxide, TCO) and one has an electrocatalytic surface (e.g., an aqueous-electrolyte coating). When light strikes the absorber, photoelectrons and holes are created. The electrons then migrate through the TCO, which acts as a current collector, and enter the electric circuit. The holes diffuse to the electrode surface, where they chemically react with water molecules and cause them to electrochemically split into oxygen gas. This gas evolves at the photoanode and can be collected in a container for any potential further use. Protons migrate through the electrolyte to the counter electrode, where they combine with electrons to form hydrogen gas, which is collected as fuel. We have designed a PEC reactor (a prototype of which is shown in Figure 1) that has a large (10 10cm) iron oxide Figure 1. The photoelectrochemical cell (PEC) reactor prototype. The device has an active area of 100cm2 and is comprised of glass coated with an iron-oxide photoelectrode. The design incorporates an oxygen gas outlet (top left). The white compartment on the right of the device holds the platinum counter electrode for hydrogen gas evolution and collection. One molar mass of potassium hydroxide, acting as the electrolyte, is supplied continuously.

International Exploratory Workshop on Catalysis, Photoelectrochemistry, and X-ray Spectroscopy for Renewable Energy

From August 17–19, 2015, the Swiss Federal Laboratories for Materials Science and Technology (Empa) and the Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI) held an international workshop on photoelectrochemistry, catalysis, and X-ray spectroscopy at Empa in Dübendorf, Switzerland. Thirty scientists from Austria, China, Germany, Italy, Japan, Korea, South Africa, Sweden, Switzerland, and the United States elaborated on novel X-ray and electron spectroscopy techniques combined operando and in situ with electroanalytical methods for renewable and sustainable energy.

Women in Physics in South Africa: A Passionate Career Development

In celebration of the world year of physics, I worked with the Department of Science and Technology (DST) to start a Women in Physics working group in South Africa. At the end of 2004, I submitted a proposal to DST to fund the formation of Women in Physics in South Africa. The DST funded the formation of the working group. This success was due to my personal interest in women in physics, which was instilled by my attendance at the first IUPAP Women in Physics Conference in Paris in 2002. The story presented here is my personal journey to becoming a physicist, despite some difficulties that I have come across in my life, and to establishing the Women in Physics Group in South Africa.