p H determination is a strong prerequisite for many biochemical and biological processes. We used... more p H determination is a strong prerequisite for many biochemical and biological processes. We used two methods, namely, the electrochemical potential method (experimental) and site binding method (theoretical), to study the sensitivity of zinc oxide (ZnO) nanorods grown on two-dimensional macroporous periodic structures (2DMPPS) (p-and n-type) and plane n-type Si substrates for use as an intracellular pH sensing device. The dimension of these nanorods varied in radius between 50 and 300 nm and lengths of 1–10 μm. We found that the sensitivity of ZnO nanorods increases with reductions in size, from 35 mV/pH for D=300 nm and L=10 μm, to 58 mV/pH for D=50 nm and L=1 μm, using the site binding model. The experimental electrochemical potential difference for the ZnO nanorods working electrode versus Ag/AgCl reference electrode showed a high sensitivity range for ZnO nanorods grown on 2DMPPS n-Si substrate as compared to plane n-Si at room temperature for pH ranging from 4 to 12 in buffer and NaCl solutions.
... Muzaffer Çakar, Nezir Yıldırım, Şukru Karataş, Cabir Temirci, Abdulmecit Türüt. ... Therefore... more ... Muzaffer Çakar, Nezir Yıldırım, Şukru Karataş, Cabir Temirci, Abdulmecit Türüt. ... Therefore, the SBH determined from the zero bias intercept, assuming thermionic emission as the current transport ... CJHuang, S.Han, D.Groze, A.Turak, and ZHLu, Organic light-emitting devices with ...
Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of ve... more Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires were performed quantitatively by nanoindentation technique. These nanostructures were grown by the vapor liquid solid ͑VLS͒ method, a relatively high temperature approach, and the aqueous chemical growth ͑ACG͒ method, a relatively low temperature approach on different substrates, including SiC and Si. The first critical load at the inflection point found for the ZnO nanorods/nanowires grown by ACG method was 105 N on the SiC substrates and 114 N on the Si substrates. The corresponding buckling energies calculated from the force-displacement curves were 3.15ϫ 10 −12 and 2.337ϫ 10 −12 J, respectively. Similarly, for the samples grown by the VLS method, the first critical load at the inflection point and the corresponding buckling energies were calculated from the force-displacement curves as 198 N and 7.03ϫ 10 −12 J on the SiC substrates, and 19 N and 1.805ϫ 10 −13 J on the Si substrates. Moreover, the critical buckling stress, strain, and strain energy were also calculated for all samples. The strain energy for all samples was much less than the corresponding buckling energy. This shows that our as-grown samples are elastic and flexible. The elasticity measurement was performed for all the samples before reaching the first critical and kinking inflection point, and we subsequently observed the bending flexibility, kinking, and buckling phenomena on the same nanorods/nanowires. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical, and also that the highest point on the bending curves and the first inflection and critical point were very close. ZnO nanorods/nanowires grown on SiC by the ACG method, and those grown by the VLS method on Si substrates, show a linear relation and high modulus of elasticity for the force and displacement up to the first inflection and critical point. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point, is independent of the growth method and is strongly dependent on the verticality on the surface of the substrates. In addition, the results show that after the first buckling point, the nanorods/nanowires have plasticity, and become more flexible to produce multiple kinks.
Zinc Oxide (ZnO) has many promising properties for optoelectronics, sensor applications, transpar... more Zinc Oxide (ZnO) has many promising properties for optoelectronics, sensor applications, transparent electronics etc. To mention a few, ZnO has a large exciton binding energy (60 meV at room temperature) and a direct wide bandgap energy of 3.37 eV. In addition, ZnO is piezoelectric and shows more resistance to radiation damage than Si and GaN. The green luminescence band, or deep band emission (DBE), in ZnO has been studied for decades, but no clear consensus has been made. The first part of this thesis has been addressed to the issue of the origin of the DBE. Both an ion implantation and a systematic annealing study was performed. In the ion implantation study both Zn and O ions were implanted in different concentrations in bulk single crystal ZnO wafers. The photoluminescence (PL) intensity of the DBE decreased rapidly with increased concentration of implanted Zn ions, whereas the DBE intensity only slightly decreased with increased concentration of the implanted O ions. The comparison of DBE intensities together with PL measurements of the as-grown samples led to the conclusion that zinc vacancies (V Zn) are involved in the DBE. In the annealing study single crystalline bulk ZnO wafers were annealed in different atmospheres, especially O-and Zn-rich atmospheres, in a systematic way. All samples were characterized with PL measurement performed from 27 K to room temperature. A striking correlation between the position of the DBE and the annealing condition was observed. In particular, for samples annealed in Zn-rich atmospheres the DBE peak position was located at ∼2.53 eV at room temperature, whereas annealing in O-rich conditions resulted in a DBE peak position located at ∼2.35 eV. The former peak position was attributed to V O and the later to V Zn. Furthermore, both the V Zn-and the V O-related PL band exhibited characteristic features when the measurement temperature was decreased. The peak position of the V Zn-related band increased with decreased measurement temperature, while that of V O decreased. Secondly, phonon replicas were clearly observed in the DBE spectra in the sample containing V Zn. Finally, for the V Zn-enriched samples the decay curves showed strong wavelength dependence and generally slower decay components as compared to the sample enriched with V O. The results showed that the DBE is composed of at least two components, V Zn and V O. Both of them have their own characteristic features promoting defect identification. In the second part of the thesis growth and properties of ZnO nanorods are discussed. Both the vapor-liquid-solid (VLS) and the aqueous chemical growth method were used. Laser action was observed at room temperature from vertically aligned nanorods under optical pumping. Secondly, Schottky contacts were demonstrated on ZnO nanorods grown on glass substrates. The best Schottky contact was the as deposited Pd/ZnO contact with an ideality factor of 1.74±0.43 and a barrier height of 0.67±0.09 eV. The presence of surface states due to the high evaporation pressure is probably the reason for the high ideality factor. Finally buckling of ZnO nanorods under uniaxial compression was studied. The critical load was found to be 477 µN. The Young's modulus together with the critical buckling stress and strain for single nanorods was calculated using the Euler (for long nanorods) and Johnson (for intermediate nanorods) buckling models.
An overview of our recent results on characterization and modification of high-resistivity n-type... more An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ∼800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10−1 Ωcm is obtained and the Li content is reduced from above 1017 cm−3 to the mid 1015 cm−3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting improvement of the n-type conductivity. However, these clusters have a limited stability and start to dissociate already after 1h at 900 °C, accompanied by a decrease in the conductivity. For topic (ii), n-type doping by hydrogen implantation is shown to enhance the conductivity by about 5 orders of magnitude already in the as-implanted state. Despite substantial loss of hydrogen, the conductivity remains stable, or even increases, after annealing up to ≥600 °C, and necessary conditions for doping by hydrogen are discussed. In (iii), the origin of the commonly observed deep band emission from monocrystalline zinc oxide is investigated using a concept of annealing as-grown samples in different atmospheres. A strong influence by the atmosphere and temperature is observed and the results can be interpreted in terms of dominant effects on the emission by vacancy-related defects.
ABSTRACT Energy levels and wave functions of ground and excited states of an exciton are calculat... more ABSTRACT Energy levels and wave functions of ground and excited states of an exciton are calculated by the method of imaginary time. Energy levels as functions of radius of single and double wall nanotube are studied. Asymptotic behavior of energy levels at large and small values of the radius using perturbation theory and adiabatic approximation is considered. Spatially indirect exciton in semiconductor nanowire is also investigated. Experimental result from high quality reproducible ZnO nanowires grown by low temperature chemical engineering is presented. State of the art high brightness white light emitting diodes (HB-LEDs) are demonstrated from the grown ZnO nano-wires. The color temperature and color rendering index (CRI) of the HB-LEDs values was found to be (3250 K, 82), and (14000 K, 93), for the best LEDs, which means that the quality of light is superior to one obtained from GaN LEDs available on the market today. The role of VZn and VO on the emission responsible for the white light band as well as the peak position of this important wide band is thoroughly investigated in a systematic way.
ABSTRACT ZnO nanostructures were grown by thermal evaporation technique on (001) Si substrate and... more ABSTRACT ZnO nanostructures were grown by thermal evaporation technique on (001) Si substrate and were characterized by photoluminescence measurements, scanning electron microscope and x-ray measurements. The results show that the formation of ZnO nanostructures is strongly influenced by the growth conditions. By optimizing the growth conditions, orientated ZnO nanorods with a diameter of around 300 nm and lengths of 20–35 μm have been achieved, and they show excellent optical properties. The laser action is observed at room temperature by using optical pumping.
A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in... more A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in zinc-and oxygen-rich atmospheres. The different annealing conditions create oxygen and zinc vacancies in a controlled way in the ZnO samples. These defects are ...
High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate... more High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate. The current transport mechanisms of the diodes at room temperature (RT) have been explained in term of the space-charge-limited current model based on the energy band diagram of ZnO rods/4H-p-SiC heterostructure. The tunneling mechanism via deep-level states was found to be the main conduction process at low-applied voltage but at trap-filled limit voltage V TFL all traps are filled and the space-chargelimited current conduction dominated the current transport. From the RT current voltage measurements, the energy of the deep level trap and the trap concentration were obtained as ∼ 0.24 ± 0.02 eV and 4.4 × 10 18 cm-3 , respectively. The deep level states observed correspond to zinc interstitial (Zn i), responsible for the violet emission.
In this work we have analyzed the optical absorption of the ZnO and SnO 2 :F (FTO) films and appl... more In this work we have analyzed the optical absorption of the ZnO and SnO 2 :F (FTO) films and applied them in porous silicon light-emitting diodes. The absorption and energy gap were calculated by employing the projector augmented wave method [1] within the local density approximation and with a modeled on-site selfinteraction-like correction potential within the LDA+U SIC [2]. Experiment and theory show a good agreement when the optical absorption and optical energy gap are considered. A layer of FTO is deposited by spray pyrolysis on top of porous Si (PSi) or ZnO/(PSi) in order to make the LEDs. The morphology and roughness of the films are analyzed by Atomic Force Microscopy before and after the FTO deposition. The electrical and optical properties are studied by characteristics curves J × V, and electroluminescence intensity versus bias.
Recently zinc oxide (ZnO) has drawn attention as it exhibits promising properties for making opto... more Recently zinc oxide (ZnO) has drawn attention as it exhibits promising properties for making optoelectronic devices, biosensors. In this paper we will present our recent results from research work on the fabrication of light emitting diodes (LEDs) based on n-ZnO nanorods grown on p-Si by a low temperature chemical approach. The ideality factor of the p- Si/n-ZnO junctions was found
An overview of our recent results on characterization and modification of high-resistivity n-type... more An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ∼800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10−1 Ωcm is obtained and the Li content is reduced from above 1017 cm−3 to the mid 1015 cm−3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting impr...
High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate... more High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate. The current transport mechanisms of the diodes at room temperature (RT) have been explained in term of the space-charge-limited current model based on the energy band diagram of ZnO rods/4H-p-SiC heterostructure. The tunneling mechanism via deep-level states was found to be the main conduction process at low-applied voltage but at trap-filled limit voltage V TFL all traps are filled and the space-chargelimited current conduction dominated the current transport. From the RT current voltage measurements, the energy of the deep level trap and the trap concentration were obtained as ∼ 0.24 ± 0.02 eV and 4.4 × 10 18 cm-3 , respectively. The deep level states observed correspond to zinc interstitial (Zn i), responsible for the violet emission.
A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in... more A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in zinc-and oxygen-rich atmospheres. The different annealing conditions create oxygen and zinc vacancies in a controlled way in the ZnO samples. These defects are ...
p H determination is a strong prerequisite for many biochemical and biological processes. We used... more p H determination is a strong prerequisite for many biochemical and biological processes. We used two methods, namely, the electrochemical potential method (experimental) and site binding method (theoretical), to study the sensitivity of zinc oxide (ZnO) nanorods grown on two-dimensional macroporous periodic structures (2DMPPS) (p-and n-type) and plane n-type Si substrates for use as an intracellular pH sensing device. The dimension of these nanorods varied in radius between 50 and 300 nm and lengths of 1–10 μm. We found that the sensitivity of ZnO nanorods increases with reductions in size, from 35 mV/pH for D=300 nm and L=10 μm, to 58 mV/pH for D=50 nm and L=1 μm, using the site binding model. The experimental electrochemical potential difference for the ZnO nanorods working electrode versus Ag/AgCl reference electrode showed a high sensitivity range for ZnO nanorods grown on 2DMPPS n-Si substrate as compared to plane n-Si at room temperature for pH ranging from 4 to 12 in buffer ...
p H determination is a strong prerequisite for many biochemical and biological processes. We used... more p H determination is a strong prerequisite for many biochemical and biological processes. We used two methods, namely, the electrochemical potential method (experimental) and site binding method (theoretical), to study the sensitivity of zinc oxide (ZnO) nanorods grown on two-dimensional macroporous periodic structures (2DMPPS) (p-and n-type) and plane n-type Si substrates for use as an intracellular pH sensing device. The dimension of these nanorods varied in radius between 50 and 300 nm and lengths of 1–10 μm. We found that the sensitivity of ZnO nanorods increases with reductions in size, from 35 mV/pH for D=300 nm and L=10 μm, to 58 mV/pH for D=50 nm and L=1 μm, using the site binding model. The experimental electrochemical potential difference for the ZnO nanorods working electrode versus Ag/AgCl reference electrode showed a high sensitivity range for ZnO nanorods grown on 2DMPPS n-Si substrate as compared to plane n-Si at room temperature for pH ranging from 4 to 12 in buffer and NaCl solutions.
... Muzaffer Çakar, Nezir Yıldırım, Şukru Karataş, Cabir Temirci, Abdulmecit Türüt. ... Therefore... more ... Muzaffer Çakar, Nezir Yıldırım, Şukru Karataş, Cabir Temirci, Abdulmecit Türüt. ... Therefore, the SBH determined from the zero bias intercept, assuming thermionic emission as the current transport ... CJHuang, S.Han, D.Groze, A.Turak, and ZHLu, Organic light-emitting devices with ...
Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of ve... more Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires were performed quantitatively by nanoindentation technique. These nanostructures were grown by the vapor liquid solid ͑VLS͒ method, a relatively high temperature approach, and the aqueous chemical growth ͑ACG͒ method, a relatively low temperature approach on different substrates, including SiC and Si. The first critical load at the inflection point found for the ZnO nanorods/nanowires grown by ACG method was 105 N on the SiC substrates and 114 N on the Si substrates. The corresponding buckling energies calculated from the force-displacement curves were 3.15ϫ 10 −12 and 2.337ϫ 10 −12 J, respectively. Similarly, for the samples grown by the VLS method, the first critical load at the inflection point and the corresponding buckling energies were calculated from the force-displacement curves as 198 N and 7.03ϫ 10 −12 J on the SiC substrates, and 19 N and 1.805ϫ 10 −13 J on the Si substrates. Moreover, the critical buckling stress, strain, and strain energy were also calculated for all samples. The strain energy for all samples was much less than the corresponding buckling energy. This shows that our as-grown samples are elastic and flexible. The elasticity measurement was performed for all the samples before reaching the first critical and kinking inflection point, and we subsequently observed the bending flexibility, kinking, and buckling phenomena on the same nanorods/nanowires. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical, and also that the highest point on the bending curves and the first inflection and critical point were very close. ZnO nanorods/nanowires grown on SiC by the ACG method, and those grown by the VLS method on Si substrates, show a linear relation and high modulus of elasticity for the force and displacement up to the first inflection and critical point. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point, is independent of the growth method and is strongly dependent on the verticality on the surface of the substrates. In addition, the results show that after the first buckling point, the nanorods/nanowires have plasticity, and become more flexible to produce multiple kinks.
Zinc Oxide (ZnO) has many promising properties for optoelectronics, sensor applications, transpar... more Zinc Oxide (ZnO) has many promising properties for optoelectronics, sensor applications, transparent electronics etc. To mention a few, ZnO has a large exciton binding energy (60 meV at room temperature) and a direct wide bandgap energy of 3.37 eV. In addition, ZnO is piezoelectric and shows more resistance to radiation damage than Si and GaN. The green luminescence band, or deep band emission (DBE), in ZnO has been studied for decades, but no clear consensus has been made. The first part of this thesis has been addressed to the issue of the origin of the DBE. Both an ion implantation and a systematic annealing study was performed. In the ion implantation study both Zn and O ions were implanted in different concentrations in bulk single crystal ZnO wafers. The photoluminescence (PL) intensity of the DBE decreased rapidly with increased concentration of implanted Zn ions, whereas the DBE intensity only slightly decreased with increased concentration of the implanted O ions. The comparison of DBE intensities together with PL measurements of the as-grown samples led to the conclusion that zinc vacancies (V Zn) are involved in the DBE. In the annealing study single crystalline bulk ZnO wafers were annealed in different atmospheres, especially O-and Zn-rich atmospheres, in a systematic way. All samples were characterized with PL measurement performed from 27 K to room temperature. A striking correlation between the position of the DBE and the annealing condition was observed. In particular, for samples annealed in Zn-rich atmospheres the DBE peak position was located at ∼2.53 eV at room temperature, whereas annealing in O-rich conditions resulted in a DBE peak position located at ∼2.35 eV. The former peak position was attributed to V O and the later to V Zn. Furthermore, both the V Zn-and the V O-related PL band exhibited characteristic features when the measurement temperature was decreased. The peak position of the V Zn-related band increased with decreased measurement temperature, while that of V O decreased. Secondly, phonon replicas were clearly observed in the DBE spectra in the sample containing V Zn. Finally, for the V Zn-enriched samples the decay curves showed strong wavelength dependence and generally slower decay components as compared to the sample enriched with V O. The results showed that the DBE is composed of at least two components, V Zn and V O. Both of them have their own characteristic features promoting defect identification. In the second part of the thesis growth and properties of ZnO nanorods are discussed. Both the vapor-liquid-solid (VLS) and the aqueous chemical growth method were used. Laser action was observed at room temperature from vertically aligned nanorods under optical pumping. Secondly, Schottky contacts were demonstrated on ZnO nanorods grown on glass substrates. The best Schottky contact was the as deposited Pd/ZnO contact with an ideality factor of 1.74±0.43 and a barrier height of 0.67±0.09 eV. The presence of surface states due to the high evaporation pressure is probably the reason for the high ideality factor. Finally buckling of ZnO nanorods under uniaxial compression was studied. The critical load was found to be 477 µN. The Young's modulus together with the critical buckling stress and strain for single nanorods was calculated using the Euler (for long nanorods) and Johnson (for intermediate nanorods) buckling models.
An overview of our recent results on characterization and modification of high-resistivity n-type... more An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ∼800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10−1 Ωcm is obtained and the Li content is reduced from above 1017 cm−3 to the mid 1015 cm−3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting improvement of the n-type conductivity. However, these clusters have a limited stability and start to dissociate already after 1h at 900 °C, accompanied by a decrease in the conductivity. For topic (ii), n-type doping by hydrogen implantation is shown to enhance the conductivity by about 5 orders of magnitude already in the as-implanted state. Despite substantial loss of hydrogen, the conductivity remains stable, or even increases, after annealing up to ≥600 °C, and necessary conditions for doping by hydrogen are discussed. In (iii), the origin of the commonly observed deep band emission from monocrystalline zinc oxide is investigated using a concept of annealing as-grown samples in different atmospheres. A strong influence by the atmosphere and temperature is observed and the results can be interpreted in terms of dominant effects on the emission by vacancy-related defects.
ABSTRACT Energy levels and wave functions of ground and excited states of an exciton are calculat... more ABSTRACT Energy levels and wave functions of ground and excited states of an exciton are calculated by the method of imaginary time. Energy levels as functions of radius of single and double wall nanotube are studied. Asymptotic behavior of energy levels at large and small values of the radius using perturbation theory and adiabatic approximation is considered. Spatially indirect exciton in semiconductor nanowire is also investigated. Experimental result from high quality reproducible ZnO nanowires grown by low temperature chemical engineering is presented. State of the art high brightness white light emitting diodes (HB-LEDs) are demonstrated from the grown ZnO nano-wires. The color temperature and color rendering index (CRI) of the HB-LEDs values was found to be (3250 K, 82), and (14000 K, 93), for the best LEDs, which means that the quality of light is superior to one obtained from GaN LEDs available on the market today. The role of VZn and VO on the emission responsible for the white light band as well as the peak position of this important wide band is thoroughly investigated in a systematic way.
ABSTRACT ZnO nanostructures were grown by thermal evaporation technique on (001) Si substrate and... more ABSTRACT ZnO nanostructures were grown by thermal evaporation technique on (001) Si substrate and were characterized by photoluminescence measurements, scanning electron microscope and x-ray measurements. The results show that the formation of ZnO nanostructures is strongly influenced by the growth conditions. By optimizing the growth conditions, orientated ZnO nanorods with a diameter of around 300 nm and lengths of 20–35 μm have been achieved, and they show excellent optical properties. The laser action is observed at room temperature by using optical pumping.
A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in... more A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in zinc-and oxygen-rich atmospheres. The different annealing conditions create oxygen and zinc vacancies in a controlled way in the ZnO samples. These defects are ...
High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate... more High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate. The current transport mechanisms of the diodes at room temperature (RT) have been explained in term of the space-charge-limited current model based on the energy band diagram of ZnO rods/4H-p-SiC heterostructure. The tunneling mechanism via deep-level states was found to be the main conduction process at low-applied voltage but at trap-filled limit voltage V TFL all traps are filled and the space-chargelimited current conduction dominated the current transport. From the RT current voltage measurements, the energy of the deep level trap and the trap concentration were obtained as ∼ 0.24 ± 0.02 eV and 4.4 × 10 18 cm-3 , respectively. The deep level states observed correspond to zinc interstitial (Zn i), responsible for the violet emission.
In this work we have analyzed the optical absorption of the ZnO and SnO 2 :F (FTO) films and appl... more In this work we have analyzed the optical absorption of the ZnO and SnO 2 :F (FTO) films and applied them in porous silicon light-emitting diodes. The absorption and energy gap were calculated by employing the projector augmented wave method [1] within the local density approximation and with a modeled on-site selfinteraction-like correction potential within the LDA+U SIC [2]. Experiment and theory show a good agreement when the optical absorption and optical energy gap are considered. A layer of FTO is deposited by spray pyrolysis on top of porous Si (PSi) or ZnO/(PSi) in order to make the LEDs. The morphology and roughness of the films are analyzed by Atomic Force Microscopy before and after the FTO deposition. The electrical and optical properties are studied by characteristics curves J × V, and electroluminescence intensity versus bias.
Recently zinc oxide (ZnO) has drawn attention as it exhibits promising properties for making opto... more Recently zinc oxide (ZnO) has drawn attention as it exhibits promising properties for making optoelectronic devices, biosensors. In this paper we will present our recent results from research work on the fabrication of light emitting diodes (LEDs) based on n-ZnO nanorods grown on p-Si by a low temperature chemical approach. The ideality factor of the p- Si/n-ZnO junctions was found
An overview of our recent results on characterization and modification of high-resistivity n-type... more An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ∼800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10−1 Ωcm is obtained and the Li content is reduced from above 1017 cm−3 to the mid 1015 cm−3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting impr...
High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate... more High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate. The current transport mechanisms of the diodes at room temperature (RT) have been explained in term of the space-charge-limited current model based on the energy band diagram of ZnO rods/4H-p-SiC heterostructure. The tunneling mechanism via deep-level states was found to be the main conduction process at low-applied voltage but at trap-filled limit voltage V TFL all traps are filled and the space-chargelimited current conduction dominated the current transport. From the RT current voltage measurements, the energy of the deep level trap and the trap concentration were obtained as ∼ 0.24 ± 0.02 eV and 4.4 × 10 18 cm-3 , respectively. The deep level states observed correspond to zinc interstitial (Zn i), responsible for the violet emission.
A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in... more A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in zinc-and oxygen-rich atmospheres. The different annealing conditions create oxygen and zinc vacancies in a controlled way in the ZnO samples. These defects are ...
p H determination is a strong prerequisite for many biochemical and biological processes. We used... more p H determination is a strong prerequisite for many biochemical and biological processes. We used two methods, namely, the electrochemical potential method (experimental) and site binding method (theoretical), to study the sensitivity of zinc oxide (ZnO) nanorods grown on two-dimensional macroporous periodic structures (2DMPPS) (p-and n-type) and plane n-type Si substrates for use as an intracellular pH sensing device. The dimension of these nanorods varied in radius between 50 and 300 nm and lengths of 1–10 μm. We found that the sensitivity of ZnO nanorods increases with reductions in size, from 35 mV/pH for D=300 nm and L=10 μm, to 58 mV/pH for D=50 nm and L=1 μm, using the site binding model. The experimental electrochemical potential difference for the ZnO nanorods working electrode versus Ag/AgCl reference electrode showed a high sensitivity range for ZnO nanorods grown on 2DMPPS n-Si substrate as compared to plane n-Si at room temperature for pH ranging from 4 to 12 in buffer ...
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Papers by Peter Klason