Jackie Nel | University of Pretoria (original) (raw)

Papers by Jackie Nel

MRS Proceedings, 2006

Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiatio... more Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiation. The kinetic energies of irradiated protons were 2.32, 2.55 and 2.97 MeV, and for each energy condition, doses of 1 Â 10 11 , 1 Â 10 12 and 1 Â 10 13 cm À2 were given. By modulating the kinetic energy, the proton penetration depth into Si crystal could be adjusted to the range of 55-90 mm, and then controlled to the special depth regions such as junction region, depletion region and neutral region over the depletion layer in the p þ-n-n þ diode structure. Defects produced by the proton irradiation affected to electrical property of the Si diode because of their carrier trapping, and then the reverse recovery time was improved from 240 to 50 ns. It appeared that the defect states with activation energies of 0.47 and 0.54 eV may be responsible for the decrease of the minority carrier lifetime in the proton-irradiated diode with 2.97 MeV energy and 1 Â 10 13 cm À2 doses.

Applied Physics Letters, Oct 9, 2006

The authors have employed deep level transient spectroscopy to investigate the defects introduced... more The authors have employed deep level transient spectroscopy to investigate the defects introduced in n-type Ge during 160keV indium (In) ion implantation. Our results show that In implantation introduces three prominent electron traps with energy levels at EC−0.09eV, EC−0.15eV, and EC−0.30eV, respectively. The authors have found that these defects are different from the point defects introduced by electron irradiation but that they do not involve In. Annealing at 600°C removed all the defects introduced during In implantation but results in a single prominent defect with a level at EC−0.35eV.

Physica B-condensed Matter, May 1, 2012

The variation in electrical characteristics of Au/n-Ge (100) Schottky contacts have been systemat... more The variation in electrical characteristics of Au/n-Ge (100) Schottky contacts have been systematically investigated as a function of temperature using current-voltage (I-V) measurements in the temperature range 140-300 K. The I-V characteristics of the diodes indicate very strong temperature dependence. While the ideality factor n decreases, the zerobias Schottky barrier height (SBH) (B ) increases with increasing temperature. The I-V characteristics are analyzed using the thermionic emission (TE) model and the assumption of a Gaussian distribution of the barrier heights due to barrier inhomogeneities at the metal-semiconductor interface. The zero-bias barrier height B  versus 1/2kT plot has been used to show evidence of a Gaussian distribution of barrier heights and values of B  = 0.615 eV and standard deviation 0 s  = 0.0858 eV for the mean barrier height and zero-bias standard deviation have been obtained from this plot, respectively. The Richardson constant and the mean barrier height from the modified Richardson plot were obtained as 1.37 Acm-2 K-2 and 0.639 eV, respectively. This Richardson constant is much smaller than the reported of 50 Acm-2 K-2. This may be due to greater inhomogeneities at the interface.

Journal of Electronic Materials, Mar 22, 2019

Ni/4H-SiC Schottky barrier diodes have been irradiated by 5.4-MeV helium ions at cryogenic temper... more Ni/4H-SiC Schottky barrier diodes have been irradiated by 5.4-MeV helium ions at cryogenic temperatures and their electrical characteristics investigated. Only the prominent native defects (E 0.11 , E 0.16 , and E 0.65) were observed before and after low-temperature irradiation at 50 K, with a baseline on the spectrum observed starting at 190 K. Low-temperature irradiation reduced the concentration of native E 0.11 and E 0.16 defects. After annealing at 380 K, E 0.37 , E 0.58 , E 0.62 , E 0.73 , and E 0.92 defects were observed. These results show that E 0.62 , an acceptor level of the Z 1 center, and E 0.73 , an acceptor level of the Z 2 center, are both secondary defects which are not formed directly from the irradiation process but from succeeding thermal reactions. An interpretation of the formation of the secondary defects is given.

Materials Science in Semiconductor Processing, Jul 1, 2018

We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten usi... more We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten using deep-level transient spectroscopy (DLTS). Current-voltage and capacitancevoltage measurements showed a deterioration of diode thermionic emission characteristics due to the sputter deposition. Two electrically active defects E 0.29 and E 0.69 were introduced. Depth profiling revealed that sputter deposition increases the concentration of the native Z 1 defect. A comparison with prominent irradiation and process induced defects showed that the E 0.29 was unique and introduced during sputter deposition only. The E 0.69 may be silicon vacancy related defect.

Journal of Applied Physics, Apr 28, 2018

Defects introduced by the solid state reactions between tungsten and silicon carbide have been st... more 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 E 0.08 , E 0.15 , E 0.23 , E 0.34 , E 0.35 , E 0.61 , E 0.67 , and E 0.82 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.

Journal of Alloys and Compounds, Feb 1, 2012

Iridium (Ir) Schottky barrier diodes were deposited on bulk grown (100) Sbdoped n-type germanium ... more Iridium (Ir) Schottky barrier diodes were deposited on bulk grown (100) Sbdoped 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 (100) was observed up to annealing temperature of 500 o 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 (100) system occurs between 600-700 o C.

Materials Science in Semiconductor Processing, Aug 1, 2006

ABSTRACT

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Dec 1, 2019

We have used confocal Raman spectroscopy, atomic force microscopy (AFM), Binary collision approxi... more We have used confocal Raman spectroscopy, atomic force microscopy (AFM), Binary collision approximations and Deep level transient spectroscopy (DLTS) to study the defects introduced in n-type 4H-SiC by 167 MeV Xe 26+ ions (swift heavy ions (SHIs)). Moderately doped epitaxial layers were irradiated with SHIs to a fluence of 5 × 10 11 cm −2 at room temperature. Raman spectroscopy was used to investigate the effects of irradiation on the crystal structure. Raman intensity reduced after irradiation but the overall bond structure was conserved. Cluster spectra from confocal Raman spectroscopy showed a damage impact that was consistent with SRIM simulations. AFM showed that the incident radiation resulted in elongated protrusions. The virgin samples contained the E 0.09 , E 0.12 , E 0.15 and E 0.65 as the only electrically active defects. After irradiation the E 0.40 and E 0.71 defects were introduced. 2. Experimental details and binary collision approximation (BCA) methodology Nitrogen doped, n-type (0001) oriented 4H-SiC (8°off axis) wafers supplied by Cree inc were used. The wafers consisted of a 6.0 µm epitaxial layer of doping density 6 × 10 16 cm −3 grown on a highly doped substrate of approximately 10 18 cm −3. The samples were cleaned in a two-step procedure that involved degreasing and then wet etching. Degreasing was done by boiling for 5 min each in trichloroethylene, acetone then methanol followed by rinsing in deionised water 18.2 MΩ

Superlattices and Microstructures, 2006

We have investigated and compared the defects in ZnO grown by two methods, namely seeded chemical... more We have investigated and compared the defects in ZnO grown by two methods, namely seeded chemical vapour transport (SCVT) and melt-growth (MG), using conventional deep level transient spectroscopy (DLTS) and high resolution (Laplace) DLTS with Au and Ru Schottky barrier diodes. Both materials contained two prominent defects, E1, at EC–0.12 eV and E3 at EC–0.29 eV. The SCVT ZnO has E1 as

MRS Proceedings, 2006

Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiatio... more Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiation. The kinetic energies of irradiated protons were 2.32, 2.55 and 2.97 MeV, and for each energy condition, doses of 1 Â 10 11 , 1 Â 10 12 and 1 Â 10 13 cm À2 were given. By modulating the kinetic energy, the proton penetration depth into Si crystal could be adjusted to the range of 55-90 mm, and then controlled to the special depth regions such as junction region, depletion region and neutral region over the depletion layer in the p þ-n-n þ diode structure. Defects produced by the proton irradiation affected to electrical property of the Si diode because of their carrier trapping, and then the reverse recovery time was improved from 240 to 50 ns. It appeared that the defect states with activation energies of 0.47 and 0.54 eV may be responsible for the decrease of the minority carrier lifetime in the proton-irradiated diode with 2.97 MeV energy and 1 Â 10 13 cm À2 doses.

Semiconductor Science and Technology

Gallium nitride thin films have attracted attention due to their prospects in semiconductor devic... more Gallium nitride thin films have attracted attention due to their prospects in semiconductor devices and technology. In this study, we investigate the electrical properties and perform deep level transient spectroscopy (DLTS) on Au/Ni Schottky diodes fabricated on gallium nitride thin films that were synthesized by electrodeposition on a Si(111) substrate from a solution containing gallium nitrate (Ga(NO3)3) and ammonium nitrate (NH4(NO3)) using current densities of 1 and 3 mA cm−2. The thin films were found to crystallize in the wurtzite hexagonal structure with crystallite sizes of approximately 20 nm. Scanning electron microscopy and atomic force microscopy were used to characterize the microstructure of the GaN thin films. The Schottky diodes had good rectifying properties, corresponding to n-type material. The diodes had a IV barrier heights of 0.76 eV and 0.60 eV; a CV barrier heights of 0.92 eV and 0.71 eV; and carrier densities of 1.2 × 1016 cm−3, and 1.7 × 1016 cm−3, for mat...

Fifth Conference on Sensors, MEMS, and Electro-Optic Systems, 2019

ZnO thin films were produced by the spin-coating sol-gel method on which the nanorods were grown ... more ZnO thin films were produced by the spin-coating sol-gel method on which the nanorods were grown by chemical bath deposition. The morphology of the thin films and nanorods were studied using field emission scanning electron microscopy (SEM), and the structure of the ZnO was determined by X-ray diffraction. It was found that the thin films comprised of randomly orientated particles (~57 nm in size) which covered the entire surface, although there were some voids visible in the films. The nanorods were found to have preferred orientation along the (002) direction, and this was confirmed by the SEM images which also indicated that the nanorods were of uniform size and height. Raman spectroscopy showed that both the thin films and the nanorods contained defects. The electrical properties of the thin films were studied before and after alpha particle irradiation.

Physica Status Solidi A-applications and Materials Science, Oct 1, 2012

We have used deep level transient spectroscopy (DLTS) and high resolution DLTS to characterize th... more We have used deep level transient spectroscopy (DLTS) and high resolution DLTS to characterize the defects introduced in epitaxially grown n‐type, P‐doped, Si during electron beam deposition (EBD) of Pt for Schottky contact formation. The identity of some of these defects could be established by comparing their properties to those of well‐known defects introduced by high energy electron irradiation of the same material. The most prominent EBD‐induced defects thus identified were the E‐center (VP center), the A‐center (VO center), interstitial carbon (Ci), and the interstitial carbon–substitutional carbon (CiCs) pair. EBD also introduced some defects that were not observed after high energy electron irradiation. DLTS depth profiling revealed that the main defects, VO and VP, could be detected up to 0.5 µm below the metal–Si interface. Shielding the sample from particles originating in the region of the electron beam significantly reduced defect introduction and resulted in Schottky contacts with improved rectification properties. Finally, we have found that exposing the sample to EBD conditions, without actually depositing metal, introduced a different set of electron traps, not introduced by the EBD process.

Journal of Electronic Materials, Sep 21, 2007

We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten usi... more We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten using deep-level transient spectroscopy (DLTS). Current-voltage and capacitancevoltage measurements showed a deterioration of diode thermionic emission characteristics due to the sputter deposition. Two electrically active defects E 0.29 and E 0.69 were introduced. Depth profiling revealed that sputter deposition increases the concentration of the native Z 1 defect. A comparison with prominent irradiation and process induced defects showed that the E 0.29 was unique and introduced during sputter deposition only. The E 0.69 may be silicon vacancy related defect.

Agriculture

Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ... more Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ticks. Due to misuse in rural dipping pools, some ticks are showing resistance to Taktic. This work presents a low-cost e-nose with commercial sensors to monitor Taktic levels in dipping pool water. The device shows distinctly different measurements for the odours of air, distilled water, farm water, and four levels of Taktic insecticide in farm water. A naive Bayes algorithm with a Gaussian distribution is trained on the data and a validation set achieves a 96.5% accuracy. This work also compares two sol-gel ZnO nanoparticle solutions with an off-the-shelf ZnO nanoparticle ink for use as active material in chemiresistive gas sensors to be employed in an e-nose array. The ZnO solutions are screen-printed onto gold electrodes, auto-sintered with a built in heater, and used with UV illumination to operate as low-power, room temperature gas sensors. All of the screen-printed ZnO sensors sho...

Physica Status Solidi A-applications and Materials Science, 2008

ABSTRACT

ECS Meeting Abstracts, 2020

Group III-nitride semiconductor materials show promise in a variety of electronics applications, ... more Group III-nitride semiconductor materials show promise in a variety of electronics applications, including diodes, transistors, LEDs and photovoltaic applications. The new generation of semiconductors rely heavily on nanotechnology and advances in nanomaterials. Group III-nitride semiconductor materials such as GaN, AlN and InN are promising materials since their properties are ideal for use in optoelectronic devices, high power and high temperature electronic devices. These materials have wide band gaps between 1.9 and 6.3 eV and, for electronic applications, these materials are usually synthesised by means of chemical vapour deposition or molecular beam epitaxy. These techniques are expensive, therefore we investigated room temperature electrochemical growth to synthesize GaN. The advantages of electrochemical deposition are the controllability of the thickness and surface morphology by varying the deposition parameters, cost-effectiveness, the minimum waste generation, long bath ...

Materials Science in Semiconductor Processing, 2019

ZnO thin films were prepared using the sol-gel spin coating technique. The structure was investig... more ZnO thin films were prepared using the sol-gel spin coating technique. The structure was investigated using Xray diffraction (XRD). The XRD spectra exhibited typical randomly orientated structure with a slight preference for growth along the (002) plane and a crystallite size of ∼ 48 nm. The Schottky barrier diodes were fabricated on the synthesized ZnO thin films. The electrical properties before and after irradiating the devices with alpha particle irradiation were characterized using current-voltage (I-V), capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and Laplace-transform deep-level transient spectroscopy (L-DLTS) techniques. Pd/ ZnO/n-Si/AuSb Schottky diodes exhibited good rectifying properties. Before irradiation, the DLTS spectra revealed one defect E 4 with activation enthalpy 0.41 eV. After irradiation, there is a new defect E α with the activation enthalpy 0.35 eV. Laplace-transform deep-level transient spectroscopy (L-DLTS) revealed the fine structure of the E α to be made up of 0.53 eV and 0.36 eV defects.

MRS Proceedings, 2006

Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiatio... more Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiation. The kinetic energies of irradiated protons were 2.32, 2.55 and 2.97 MeV, and for each energy condition, doses of 1 Â 10 11 , 1 Â 10 12 and 1 Â 10 13 cm À2 were given. By modulating the kinetic energy, the proton penetration depth into Si crystal could be adjusted to the range of 55-90 mm, and then controlled to the special depth regions such as junction region, depletion region and neutral region over the depletion layer in the p þ-n-n þ diode structure. Defects produced by the proton irradiation affected to electrical property of the Si diode because of their carrier trapping, and then the reverse recovery time was improved from 240 to 50 ns. It appeared that the defect states with activation energies of 0.47 and 0.54 eV may be responsible for the decrease of the minority carrier lifetime in the proton-irradiated diode with 2.97 MeV energy and 1 Â 10 13 cm À2 doses.

Applied Physics Letters, Oct 9, 2006

The authors have employed deep level transient spectroscopy to investigate the defects introduced... more The authors have employed deep level transient spectroscopy to investigate the defects introduced in n-type Ge during 160keV indium (In) ion implantation. Our results show that In implantation introduces three prominent electron traps with energy levels at EC−0.09eV, EC−0.15eV, and EC−0.30eV, respectively. The authors have found that these defects are different from the point defects introduced by electron irradiation but that they do not involve In. Annealing at 600°C removed all the defects introduced during In implantation but results in a single prominent defect with a level at EC−0.35eV.

Physica B-condensed Matter, May 1, 2012

The variation in electrical characteristics of Au/n-Ge (100) Schottky contacts have been systemat... more The variation in electrical characteristics of Au/n-Ge (100) Schottky contacts have been systematically investigated as a function of temperature using current-voltage (I-V) measurements in the temperature range 140-300 K. The I-V characteristics of the diodes indicate very strong temperature dependence. While the ideality factor n decreases, the zerobias Schottky barrier height (SBH) (B ) increases with increasing temperature. The I-V characteristics are analyzed using the thermionic emission (TE) model and the assumption of a Gaussian distribution of the barrier heights due to barrier inhomogeneities at the metal-semiconductor interface. The zero-bias barrier height B  versus 1/2kT plot has been used to show evidence of a Gaussian distribution of barrier heights and values of B  = 0.615 eV and standard deviation 0 s  = 0.0858 eV for the mean barrier height and zero-bias standard deviation have been obtained from this plot, respectively. The Richardson constant and the mean barrier height from the modified Richardson plot were obtained as 1.37 Acm-2 K-2 and 0.639 eV, respectively. This Richardson constant is much smaller than the reported of 50 Acm-2 K-2. This may be due to greater inhomogeneities at the interface.

Journal of Electronic Materials, Mar 22, 2019

Ni/4H-SiC Schottky barrier diodes have been irradiated by 5.4-MeV helium ions at cryogenic temper... more Ni/4H-SiC Schottky barrier diodes have been irradiated by 5.4-MeV helium ions at cryogenic temperatures and their electrical characteristics investigated. Only the prominent native defects (E 0.11 , E 0.16 , and E 0.65) were observed before and after low-temperature irradiation at 50 K, with a baseline on the spectrum observed starting at 190 K. Low-temperature irradiation reduced the concentration of native E 0.11 and E 0.16 defects. After annealing at 380 K, E 0.37 , E 0.58 , E 0.62 , E 0.73 , and E 0.92 defects were observed. These results show that E 0.62 , an acceptor level of the Z 1 center, and E 0.73 , an acceptor level of the Z 2 center, are both secondary defects which are not formed directly from the irradiation process but from succeeding thermal reactions. An interpretation of the formation of the secondary defects is given.

Materials Science in Semiconductor Processing, Jul 1, 2018

We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten usi... more We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten using deep-level transient spectroscopy (DLTS). Current-voltage and capacitancevoltage measurements showed a deterioration of diode thermionic emission characteristics due to the sputter deposition. Two electrically active defects E 0.29 and E 0.69 were introduced. Depth profiling revealed that sputter deposition increases the concentration of the native Z 1 defect. A comparison with prominent irradiation and process induced defects showed that the E 0.29 was unique and introduced during sputter deposition only. The E 0.69 may be silicon vacancy related defect.

Journal of Applied Physics, Apr 28, 2018

Defects introduced by the solid state reactions between tungsten and silicon carbide have been st... more 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 E 0.08 , E 0.15 , E 0.23 , E 0.34 , E 0.35 , E 0.61 , E 0.67 , and E 0.82 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.

Journal of Alloys and Compounds, Feb 1, 2012

Iridium (Ir) Schottky barrier diodes were deposited on bulk grown (100) Sbdoped n-type germanium ... more Iridium (Ir) Schottky barrier diodes were deposited on bulk grown (100) Sbdoped 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 (100) was observed up to annealing temperature of 500 o 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 (100) system occurs between 600-700 o C.

Materials Science in Semiconductor Processing, Aug 1, 2006

ABSTRACT

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Dec 1, 2019

We have used confocal Raman spectroscopy, atomic force microscopy (AFM), Binary collision approxi... more We have used confocal Raman spectroscopy, atomic force microscopy (AFM), Binary collision approximations and Deep level transient spectroscopy (DLTS) to study the defects introduced in n-type 4H-SiC by 167 MeV Xe 26+ ions (swift heavy ions (SHIs)). Moderately doped epitaxial layers were irradiated with SHIs to a fluence of 5 × 10 11 cm −2 at room temperature. Raman spectroscopy was used to investigate the effects of irradiation on the crystal structure. Raman intensity reduced after irradiation but the overall bond structure was conserved. Cluster spectra from confocal Raman spectroscopy showed a damage impact that was consistent with SRIM simulations. AFM showed that the incident radiation resulted in elongated protrusions. The virgin samples contained the E 0.09 , E 0.12 , E 0.15 and E 0.65 as the only electrically active defects. After irradiation the E 0.40 and E 0.71 defects were introduced. 2. Experimental details and binary collision approximation (BCA) methodology Nitrogen doped, n-type (0001) oriented 4H-SiC (8°off axis) wafers supplied by Cree inc were used. The wafers consisted of a 6.0 µm epitaxial layer of doping density 6 × 10 16 cm −3 grown on a highly doped substrate of approximately 10 18 cm −3. The samples were cleaned in a two-step procedure that involved degreasing and then wet etching. Degreasing was done by boiling for 5 min each in trichloroethylene, acetone then methanol followed by rinsing in deionised water 18.2 MΩ

Superlattices and Microstructures, 2006

We have investigated and compared the defects in ZnO grown by two methods, namely seeded chemical... more We have investigated and compared the defects in ZnO grown by two methods, namely seeded chemical vapour transport (SCVT) and melt-growth (MG), using conventional deep level transient spectroscopy (DLTS) and high resolution (Laplace) DLTS with Au and Ru Schottky barrier diodes. Both materials contained two prominent defects, E1, at EC–0.12 eV and E3 at EC–0.29 eV. The SCVT ZnO has E1 as

MRS Proceedings, 2006

Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiatio... more Electrical characterization of p þ-n-n þ Si power electric diodes was done with proton irradiation. The kinetic energies of irradiated protons were 2.32, 2.55 and 2.97 MeV, and for each energy condition, doses of 1 Â 10 11 , 1 Â 10 12 and 1 Â 10 13 cm À2 were given. By modulating the kinetic energy, the proton penetration depth into Si crystal could be adjusted to the range of 55-90 mm, and then controlled to the special depth regions such as junction region, depletion region and neutral region over the depletion layer in the p þ-n-n þ diode structure. Defects produced by the proton irradiation affected to electrical property of the Si diode because of their carrier trapping, and then the reverse recovery time was improved from 240 to 50 ns. It appeared that the defect states with activation energies of 0.47 and 0.54 eV may be responsible for the decrease of the minority carrier lifetime in the proton-irradiated diode with 2.97 MeV energy and 1 Â 10 13 cm À2 doses.

Semiconductor Science and Technology

Gallium nitride thin films have attracted attention due to their prospects in semiconductor devic... more Gallium nitride thin films have attracted attention due to their prospects in semiconductor devices and technology. In this study, we investigate the electrical properties and perform deep level transient spectroscopy (DLTS) on Au/Ni Schottky diodes fabricated on gallium nitride thin films that were synthesized by electrodeposition on a Si(111) substrate from a solution containing gallium nitrate (Ga(NO3)3) and ammonium nitrate (NH4(NO3)) using current densities of 1 and 3 mA cm−2. The thin films were found to crystallize in the wurtzite hexagonal structure with crystallite sizes of approximately 20 nm. Scanning electron microscopy and atomic force microscopy were used to characterize the microstructure of the GaN thin films. The Schottky diodes had good rectifying properties, corresponding to n-type material. The diodes had a IV barrier heights of 0.76 eV and 0.60 eV; a CV barrier heights of 0.92 eV and 0.71 eV; and carrier densities of 1.2 × 1016 cm−3, and 1.7 × 1016 cm−3, for mat...

Fifth Conference on Sensors, MEMS, and Electro-Optic Systems, 2019

ZnO thin films were produced by the spin-coating sol-gel method on which the nanorods were grown ... more ZnO thin films were produced by the spin-coating sol-gel method on which the nanorods were grown by chemical bath deposition. The morphology of the thin films and nanorods were studied using field emission scanning electron microscopy (SEM), and the structure of the ZnO was determined by X-ray diffraction. It was found that the thin films comprised of randomly orientated particles (~57 nm in size) which covered the entire surface, although there were some voids visible in the films. The nanorods were found to have preferred orientation along the (002) direction, and this was confirmed by the SEM images which also indicated that the nanorods were of uniform size and height. Raman spectroscopy showed that both the thin films and the nanorods contained defects. The electrical properties of the thin films were studied before and after alpha particle irradiation.

Physica Status Solidi A-applications and Materials Science, Oct 1, 2012

We have used deep level transient spectroscopy (DLTS) and high resolution DLTS to characterize th... more We have used deep level transient spectroscopy (DLTS) and high resolution DLTS to characterize the defects introduced in epitaxially grown n‐type, P‐doped, Si during electron beam deposition (EBD) of Pt for Schottky contact formation. The identity of some of these defects could be established by comparing their properties to those of well‐known defects introduced by high energy electron irradiation of the same material. The most prominent EBD‐induced defects thus identified were the E‐center (VP center), the A‐center (VO center), interstitial carbon (Ci), and the interstitial carbon–substitutional carbon (CiCs) pair. EBD also introduced some defects that were not observed after high energy electron irradiation. DLTS depth profiling revealed that the main defects, VO and VP, could be detected up to 0.5 µm below the metal–Si interface. Shielding the sample from particles originating in the region of the electron beam significantly reduced defect introduction and resulted in Schottky contacts with improved rectification properties. Finally, we have found that exposing the sample to EBD conditions, without actually depositing metal, introduced a different set of electron traps, not introduced by the EBD process.

Journal of Electronic Materials, Sep 21, 2007

We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten usi... more We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten using deep-level transient spectroscopy (DLTS). Current-voltage and capacitancevoltage measurements showed a deterioration of diode thermionic emission characteristics due to the sputter deposition. Two electrically active defects E 0.29 and E 0.69 were introduced. Depth profiling revealed that sputter deposition increases the concentration of the native Z 1 defect. A comparison with prominent irradiation and process induced defects showed that the E 0.29 was unique and introduced during sputter deposition only. The E 0.69 may be silicon vacancy related defect.

Agriculture

Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ... more Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ticks. Due to misuse in rural dipping pools, some ticks are showing resistance to Taktic. This work presents a low-cost e-nose with commercial sensors to monitor Taktic levels in dipping pool water. The device shows distinctly different measurements for the odours of air, distilled water, farm water, and four levels of Taktic insecticide in farm water. A naive Bayes algorithm with a Gaussian distribution is trained on the data and a validation set achieves a 96.5% accuracy. This work also compares two sol-gel ZnO nanoparticle solutions with an off-the-shelf ZnO nanoparticle ink for use as active material in chemiresistive gas sensors to be employed in an e-nose array. The ZnO solutions are screen-printed onto gold electrodes, auto-sintered with a built in heater, and used with UV illumination to operate as low-power, room temperature gas sensors. All of the screen-printed ZnO sensors sho...

Physica Status Solidi A-applications and Materials Science, 2008

ABSTRACT

ECS Meeting Abstracts, 2020

Group III-nitride semiconductor materials show promise in a variety of electronics applications, ... more Group III-nitride semiconductor materials show promise in a variety of electronics applications, including diodes, transistors, LEDs and photovoltaic applications. The new generation of semiconductors rely heavily on nanotechnology and advances in nanomaterials. Group III-nitride semiconductor materials such as GaN, AlN and InN are promising materials since their properties are ideal for use in optoelectronic devices, high power and high temperature electronic devices. These materials have wide band gaps between 1.9 and 6.3 eV and, for electronic applications, these materials are usually synthesised by means of chemical vapour deposition or molecular beam epitaxy. These techniques are expensive, therefore we investigated room temperature electrochemical growth to synthesize GaN. The advantages of electrochemical deposition are the controllability of the thickness and surface morphology by varying the deposition parameters, cost-effectiveness, the minimum waste generation, long bath ...

Materials Science in Semiconductor Processing, 2019

ZnO thin films were prepared using the sol-gel spin coating technique. The structure was investig... more ZnO thin films were prepared using the sol-gel spin coating technique. The structure was investigated using Xray diffraction (XRD). The XRD spectra exhibited typical randomly orientated structure with a slight preference for growth along the (002) plane and a crystallite size of ∼ 48 nm. The Schottky barrier diodes were fabricated on the synthesized ZnO thin films. The electrical properties before and after irradiating the devices with alpha particle irradiation were characterized using current-voltage (I-V), capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and Laplace-transform deep-level transient spectroscopy (L-DLTS) techniques. Pd/ ZnO/n-Si/AuSb Schottky diodes exhibited good rectifying properties. Before irradiation, the DLTS spectra revealed one defect E 4 with activation enthalpy 0.41 eV. After irradiation, there is a new defect E α with the activation enthalpy 0.35 eV. Laplace-transform deep-level transient spectroscopy (L-DLTS) revealed the fine structure of the E α to be made up of 0.53 eV and 0.36 eV defects.