This paper presents the experimental design and characterization of an optimized radio-frequency energy-harvesting prototype device to operate in the GSM 900 band. The energy harvesting device is based on an off-the-shelf GSM antenna, Schottky diode rectifier, and was implemented on a standard FR4 substrate. The experimental results show that the harvesting device is capable of generating 0.3 V DC voltage at an input power of -17 dBm at 956 MHz frequency. The measured efficiency of the developed energy harvesting system was 68%, at R-L = 1.6 k ohm, which is a very significant performance relative to other prototypes of the same class reported in literature.

Barrier height inhomogeneities on Pd/n-type 4H-SiC Schottky barrier diodes in the 300-800 K temperature range have been investigated. Palladium is known to form silicide above 673 K. Temperature dependent current-voltage (I-V) characteristics were analyzed. Barrier height (BH) and ideality factor (n) were found to be strongly temperature dependent. Barrier height increased, whilst ideality factor decreased with increasing in temperature and the Richardson plot showed some deviation from linearity. This was attributed to barrier inhomogeneities at the metal-semiconductor interface which resulted in a distribution of barrier heights. From the modified Richardson plot, the modified Richardson constant, A** was found to be 155 Acm(-2)K(-2) and 87 Acm(-2)K(-2) in the 300-525 K and the 550-800 K temperature ranges respectively.

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.

We have investigated the current-voltage (I-V) characteristics of nickel (Ni), cobalt (Co), tungsten (W) and palladium (Pd) Schottky contacts on n-type 4H-SiC in the 300–800K temperature range. Results extracted from I-V measurements of Schottky barrier diodes showed that barrier height (ФBo) and ideality factor (n) were strongly dependent on temperature. Schottky barrier heights for contacts of all the metals showed an increase with temperature between 300K and 800K. This was attributed to barrier inhomogeneities at the interface between the metal and the semiconductor, which resulted in a distribution of barrier heights at the interface. Ideality factors of Ni, Co and Pd decreased from 1.6 to 1.0 and for W the ideality factor decreased from 1.1 to 1.0 when the temperature was increased from 300K to 800K respectively. The device parameters were compared to assess advantages and disadvantages of the metals for envisaged applications.

The Recently, there has been growing interest in power conditioning interface circuits used to enhance energy harvesting using piezoelectric devices. Among there interface circuits, the Synchronised Switch Harvesting on Inductor Interfaces (SSHI) and Synchronous Electric Charge Extraction (SECE) are the most promising. In this paper we the results of design and performance characterisation of self-powered SSHI and SECE interface circuits. The self-powered SSHI interface demonstrated a record enhancement of close to 300 % while the self-powered SECE interface shoed an enhancement of 70 % more power relative to the standard energy harvesting (SEH)

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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, the T2 deep level defect was observed in all other ambient conditions except in Ar. The emission properties of the E3 deep level defect are observed to change with increase in annealing temperature beyond 800 °C. For samples annealed beyond 800 °C, a decrease in activation enthalpy with increase in annealing temperature has been observed which suggests an enhanced thermal ionization rate of E3 with annealing.

We report on the studies carried out on hydrogen peroxide treated melt-grown, bulk single crystal ZnO samples. Results show the existence of two shallow donors in the as-received ZnO samples with energy levels (37.8±0.3)meV that has been suggested as Zni related and possibly H-complex related and (54.5±0.9)meV, which has been assigned to an Al-related donor. Annealing studies performed on the hydrogen peroxide treated samples reveal the existence of a conductive channel in the samples in which new energy levels have been observed, Zn vacancies, related to the Group I elements, XZn. The surface donor volume concentration of the conductive channel was calculated from a theory developed by Look (2007) [1]. Results indicate an increase in the surface volume concentration with increasing annealing temperature from 60×1017cm−3 at 200°C to 4.37×1018cm-3 at 800°C.

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 energy levels.

Iridium (Ir) Schottky barrier diodes were deposited on bulk grown (1 0 0) Sb-doped n-type germanium by using the electron beam deposition system. Electrical characterization of these contacts using current-voltage (I-V) and capacitance-voltage (C-V) measurements was performed under various annealing conditions. The variation of the electrical properties of these Schottky diodes can be attributed to combined effects of interfacial reaction and phase transformation during the annealing process. Thermal stability of the Ir/n-Ge (1 0 0) was observed up to annealing temperature of 500 degrees C. Furthermore, structural characterization of these samples was performed by using a scanning electron microscopy (SEM) at different annealing temperatures. Results have also revealed that the onset temperature for agglomeration in a 20 nm Ir/n-Ge (1 0 0) system occurs between 600 and 700 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

A systematic investigation to check the quality of Pd Schottky contacts deposited on ZnO has been performed on electron beam (e-beam) deposited and resistively/thermally evaporated samples using current-voltage, IV, and conventional deep level transient spectroscopy (DLTS) measurements. Room temperature IV measurements reveal the dominance of pure thermionic emission on the resistively evaporated contacts, while the e-beam deposited contacts show the dominance of generation recombination at low voltages, <0.30 V, and the dominance of pure thermionic emission at high voltages, greater than 0.30 V. The resistively evaporated contacts have very low reverse currents of the order of 10−10 A at a reverse voltage of 1.0 V whereas the e-beam deposited contacts have reverse currents of the order of 10−6 A at 1.0 V. Average ideality factors have been determined as (1.43 ± 0.01) and (1.66 ± 0.02) for the resistively evaporated contacts and e-beam deposited contacts, respectively. The IV barrier heights have been calculated as (0.721 ± 0.002) eV and (0.624 ± 0.005) eV for the resistively evaporated and e-beam deposited contacts, respectively. Conventional DLTS measurements reveal the presence of three prominent defects in both the resistive and e-beam contacts. Two extra peaks with energy levels of 0.60 and 0.81 eV below the conduction band minimum have been observed in the e-beam deposited contacts. These have been explained as contributing to the generation recombination current that dominates at low voltages and high leakage currents. Based on the reverse current at 1.0 V, the degree of rectification, the dominant current transport mechanism and the observed defects, we conclude that the resistive evaporation technique yields better quality Schottky contacts for use in solar cells and ultraviolet detectors compared to the e-beam deposition technique. The 0.60 eV has been identified as possibly related to the unoccupied level for the doubly charged oxygen vacancy, Vo2+.

Current-voltage (IV) and capacitance-voltage (CV) measurement techniques have successfully been employed to study the effects of annealing highly rectifying Pd/ZnO Schottky contacts. IV results reveal a decrease in the contact quality with increasing annealing temperature as confirmed by a decrease in the zero bias barrier height and an increase in the reverse current measured at -1.5 V. An average barrier height of (0.77 +/- 0.02) eV has been calculated by assuming pure thermionic emission for the as-deposited material and as (0.56 +/- 0.03) eV after annealing at 550 degrees C. The reverse current has been measured as (2.10 +/- 0.01) x 10(-10) A for the as-deposited and increases by 5 orders of magnitude after annealing at 550 degrees C to (1.56 +/- 0.01) x 10(-5) A. The depletion layer width measured at -2.0 V has shown a strong dependence on thermal annealing as it decreases from 1.09 mu m after annealing at 200 degrees C to 0.24 mu m after annealing at 500 degrees C, resulting in the modification of the dopant concentration within the depletion region and hence the current flowing through the interface from pure thermionic emission to thermionic field emission with the donor concentrations increasing from 6.90 x 10(15) cm(-3) at 200 degrees C to 6.06 x 10(16) cm(-3) after annealing at 550 degrees C. This increase in the volume concentration has been explained as an effect of a conductive channel that shifts closer to the surface after sample annealing. The series resistance has been observed to decrease with increase in annealing temperature. The Pd contacts have shown high stability up to an annealing temperature of 250 degrees C as revealed by the IV and CV characteristics after which the quality of the contacts deteriorates with increase in annealing temperature. (C) 2011 Elsevier B.V. All rights reserved.

Deep level transient spectroscopy (DLTS) and Laplace-DLTS have been used to investigate the defects created in Sb doped Ge after irradiation with 2MeV protons having a fluence of 1×1013protons/cm2. The results show that proton irradiation resulted in primary hole traps at EV +0.15 and EV +0.30eV and electron traps at EC −0.38, EC −0.32, EC −0.31, EC −0.22, EC −0.20, EC −0.17, EC −0.15 and EC −0.04eV. Defects observed in this study are compared with those introduced in similar samples after MeV electron irradiation reported earlier. EC −0.31, EC −0.17 and EC −0.04, and EV +0.15eV were not observed previously in similar samples after high energy irradiation. Results from this study suggest that although similar defects are introduced by electron and proton irradiation, traps introduced by the latter are dose dependent.

We computed the homogeneous Schottky barrier height (SBH) at ideality factor (n) = 1.0 of Ni/n-Ge (100) Schottky diodes (SDs). The SDs were identically prepared by using resistive evaporation of Ni on n-Ge (100). The SBHs and n of these diodes (24 dots) were calculated from their experimental forward bias current-voltage (I-V) and reverse bias capacitance-voltage (C-V) measurements at room temperature. Even though the Schottky diodes were identically prepared, the values of the SBH from the I-V characteristics varied from 0.487 to 0.508 eV, the ideality factor varied from 1.34 to 1.53, and the SBH from the C-2-V characteristics varied from 0.358 to 0.418 eV. The Gaussian fits of the experimental SBH distributions obtained from the C-2-V and the I-V characteristics yielded mean SBH values of 0.401 +/- 0.015 and 0.503 +/- 0.006 eV, respectively. Furthermore, a homogeneous SBH value of approximately 0.535 eV was also computed from an extrapolation of a linear plot of the experimental SBHs versus the ideality factors. The homogeneous SBHs, rather than the effective SBHs, of individual contacts or mean values should be used to discuss the theories and the physical mechanisms that determine the SBHs of SDs.

Platinum (Pt) and titanium (Ti) Schottky barrier diodes were fabricated on bulk grown (1 0 0)Sb-doped n-type germanium using the electron beam whereas nickel (Ni) contacts were fabricated using the resistive evaporation system. Electrical characterization of these contacts using current-voltage (I-V) measurements was performed under various annealing conditions. The variation of the electrical properties of these Schottky diodes can be attributed to combined effects of interfacial reaction and phase transformation during the annealing process. The results have also revealed that Pt Schottky contacts are of a high quality, with low reverse currents in the order of (10(-5) to 10(-6)) A and as-deposited ideality factors as low as 1.09. Furthermore, the samples microstructural characterization was performed by scanning electron microscopy (SEM) at different annealing temperatures. From the results, it can be concluded that the onset temperature in 30 nm Ni- and Pt/n-Ge (1 0 0) systems occurs at 500-600 degrees C and 600-700 degrees C, respectively. (c) 2009 Elsevier B.V. All rights reserved.

Platinum (Pt), nickel (Ni), palladium (Pd) and cobalt (Co) Schottky barrier diodes were fabricated by vacuum resistive evaporation or electron beam deposition. We have studied the electrical characteristics of platinum, nickel, palladium and cobalt Schottky contacts on bulk grown (100) Sb-doped n-type germanium under various annealing conditions by current voltage (I-V) measurements. The Schottky behaviour of the metal contacts with annealing temperatures is compared. Results obtained from the electrical properties of the Schottky contacts have revealed that Pt contacts are highly thermally stable over a wide range of temperature compared to Pd, Ni and Co contacts. Furthermore, Pt Schottky contacts are of highest quality, with low reverse currents of the order (10(-6) - 10(-5) A) and as-deposited ideality factor as low as 1.09, compared to Pd, Ni, and Co Schottky contacts. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Current–voltage characteristics of Au/Ni/n-GaN Schottky contacts have been measured in the 60–320K temperature range. The zero bias barrier height, ϕbo and ideality factor, n have been studied as a function of temperature. The sharp increase in ideality factor at low temperatures has been explained as an effect of thermionic field emission. The deviation of the characteristics from the ideal thermionic behaviour is more pronounced with a decrease in temperature, in which the results obtained indicate the presence of other current transport mechanisms in the 60–280K temperature range and the dominance of pure thermionic emission current at 300K. The increase in barrier height with increasing temperature has been explained as an effect of barrier inhomogeneities.