Rashad Badran - Academia.edu (original) (raw)

Papers by Rashad Badran

MRS Proceedings, 2002

We compare the predictions of several analytical models for conductivity fluctuations in a homoge... more We compare the predictions of several analytical models for conductivity fluctuations in a homogeneous semiconductor containing discrete and distributed traps, using a Monte-Carlo simulation of the relevant multi – trapping (MT) transitions. The simulation directly embodies the statistical features associated with such processes, in a simple ‘model - independent’ approach, free of approximations and assumptions. We compare the results with those of several analytical approaches. In one, the noise spectrum is assumed to reflect separately, the characteristic individual release time constants of the various trapping centers in the material. In another, the trapping time into the ensemble of electron traps is taken to be the dominant time constant, and hence, in a material such as a-Si:H, where the trapping time into tail sates is of order 1ps, this is taken to imply that this component of the conductivity noise spectrum is unobservable in practice. Our own analytical approach, incorpo...

Materials Express, 2020

In this paper, the heterojunction diode based on n-Ga doped ZnO nanowires interconnected with dis... more In this paper, the heterojunction diode based on n-Ga doped ZnO nanowires interconnected with disks/p-Si assembly was fabricated and their low-temperature electrical properties were examined. The Ga-doped ZnO nanowires interconnected with disks were grown over p-Si substrate and studied by numerous techniques to understand the structural, compositional and morphological characteristics. Electrical properties, at lowtemperatures ranging from 77 K–295 K, were examined for the fabricated heterojunction diode assembly both in reverse and forward biased conditions which exhibited an excellent stability over all the temperature range. The detailed electrical characterizations revealed that the current decreases gradually from 1.9 μA, to 0.87 μA to 0.84 μA when temperature increases from 77 K, 100 K to 150 K and then increases gradually from 1.86 μA–3.36 μA and to 9.95 μA when temperature increases from 200 K–250 K and to 295 K, respectively. Both the highest rectifying ratio at 100 K and ...

Materials Express, 2020

Heterojunction diode based on n-ZnO nanorods/p-Silicon (Si) assembly was fabricated, examined and... more Heterojunction diode based on n-ZnO nanorods/p-Silicon (Si) assembly was fabricated, examined and reported here. Horizontal quartz tube thermal evaporation technique was used for the growth of ZnO nanorods on Si substrate. The nanorods were characterized by several techniques to examine the structural, morphological, scattering and electrical properties. Wurtzite hexagonal phase of the grown aligned nanorods was observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The appearance of a sharp Raman peak at 438 cm–1 was observed and it is related to the E2(high) mode of the wurtzite hexagonal phase of ZnO. The electrical properties of the fabricated heterojunction assembly were examined at different temperatures (298∼398 K) in both reverse and forward biased conditions, and a good stability was observed over the entire temperature range. A reduction in the turn-on and breakdown voltage was observed with increasing temperature. By increasing the temperature, the...

Journal of Nanoelectronics and Optoelectronics, 2015

ABSTRACT This paper reports the successful growth of aligned ZnO nanorods on p-Si substrate via l... more ABSTRACT This paper reports the successful growth of aligned ZnO nanorods on p-Si substrate via lowtemperature simple aqueous solution process. The prepared nanorods were examined in terms of their morphological, structural, compositional and optical properties using several analytical tools such as field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and room-temperature photoluminescence (PL) spectroscopy. The detailed characterization studies revealed that the as-grown nanorods are vertically aligned, wellcrystalline possessing wurtzite hexagonal phase, grown along the [0001] direction and possessing good optical properties. Furthermore, the prepared n-ZnO nanorods/p-Si heterojunction assembly was used to fabricate heterojunction diode. The fabricated heterojunction diode exhibits good rectifying behavior of rectification factor of 16 at voltage of 7.2 volts. High values of quality factor and series resistance of the device of ∼4 and 52 kΩ, respectively, are obtained from I–V characteristics. The high series resistance may play the role of a shunt resistance that causes a partial drop in the output current of the whole assembly.

Science of Advanced Materials, 2014

ABSTRACT Well-crystalline Sn-doped ZnO nanowires were grown on p-type silicon substrates by simpl... more ABSTRACT Well-crystalline Sn-doped ZnO nanowires were grown on p-type silicon substrates by simple non-catalytic thermal evaporation process. The prepared nanowires were examined in terms of their morphological, compositional and structural properties which revealed that the as-grown nanowires are well-crystalline Sn-doped ZnO, possessing wurtzite hexagonal phase structure and grown in very high density over whole silicon substrate. Further, the as-grown n-Sn-doped ZnO nanowires were used to fabricate n-Sn-ZnO/p-Si heterojunction diode. Temperature dependant electrical properties (294–353 K and 373–433 K) of the fabricated heterojunction diode were studied in the forward and reverse bias conditions and presented in this paper. The current–voltage characteristics at varying temperature of the heterojunction diode reveal that both the quality factor and Schottky barrier height depend on temperature. However, the mean barrier height is estimated ∼1.2 eV in one attempt of analysis when a Gaussian distribution of low barrier heights is considered and found almost ∼1 eV in another attempt when the Richardson plot is linearized. Furthermore, effective barrier heights of 0.55–0.75 eV are extracted in the temperature range 294–433 K when Tung model is used. These correspond to barrier heights of 0.93–0.35 eV extracted from C–V analysis in the same range of temperatures. Although the latter results from C–V analysis exhibit closer correlation with the Schottky barrier heights extracted from I–V analysis but the discrepancy between them still exist.

Science of Advanced Materials, 2013

ABSTRACT This paper reports the facile growth, characterization and efficient heterojunction diod... more ABSTRACT This paper reports the facile growth, characterization and efficient heterojunction diode application of wellcrystalline aligned n-ZnO nanonails. The ZnO nanonails were grown on p-Silicon substrate by facile noncatalytic thermal evaporation process. Detailed morphological and structural studies revealed that the nanonails are grown in high density, possessing well-crystalline and wurtzite hexagonal phase. X-ray diffraction and Raman scattering confirm the wurtzite hexagonal phase structure whereas room-temperature photoluminescence studies affirms good optical properties for the as-grown nanonails. The as-grown aligned ZnO nanonails grown on silicon substrate are utilized to fabricate n-ZnO/p-Si heterojunction diode. The I–V characteristics of the fabricated n-ZnO/p-Si heterojunction diode are studied at temperature <300 K and ≥300 K in the forward and reverse bias conditions. By detailed studies, it was found that the junction exhibits a diode-like behavior with a value of turn-on voltage of 5 V at almost all temperatures. The rectifying behavior of the fabricated heterojunction diode, at 5 V, is demonstrated by rectifying ratio of ∼4 at 77 K which decreases to ∼2 at 277 K. Moreover, the delivered current at this turn-on voltage is the least and in the order of ∼1 �A, at 77 K. This current gradually increases to ∼6 �A which occurs, at the same turn-on voltage, when the temperature changes in the range of 77 ≤ T ≤ 277 K and drastically increases to ∼400 �A at 427 K while the rectifying ratio is dropped to ∼0.4. For the reverse-bias voltage of 5 V, the leakage current changes from ∼10−7 A at 77 K to ∼10−3 A at 477 K. These results show that the turn-on voltage, breakdown voltage and leakage current have exhibited similar behavior in reverse bias due to the increase in temperature.

MRS Proceedings, 2000

ABSTRACTWe show that the analysis of post-transit photocurrent i(t) in a multi-trapping context t... more ABSTRACTWe show that the analysis of post-transit photocurrent i(t) in a multi-trapping context to determine the density of trapping states g(E) is capable of resolving features less than kT in width. A commonly used method uses a Laplace inversion of i(t) data giving the well-known result g(E) ∼ t i(t) but employs a delta function approximation for trap release times, which results in loss of energy resolution. We show that it is possible to retain the exponential distribution function for trap release time and solve the multi-trapping rate equations directly, giving significantly improved resolution. The analysis is performed on computer generated post-transit data for distributed and discrete traps, and compared with the earlier method and other related Fourier transform methods for determining g(E). In addition, the versatility of the new method in handling cases with either distributed traps or with discrete traps means that it can be applied to disordered materials or to cryst...

Vacuum, 2009

Two sets of hydrogenated microcrystalline silicon thin-film samples were prepared by Plasma Enhan... more Two sets of hydrogenated microcrystalline silicon thin-film samples were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique at different deposition conditions of excited power and pressure. The correlation between the crystalline volume fraction for the samples determined from Raman spectra and the excited power, pressure, absorption coefficient, refractive index and optical energy gap was discussed. The values of optical parameters (refractive index and absorption coefficient), were calculated from the transmission spectra in the range 400-2500 nm. The optical band energy gap and Urbach energy were obtained using the calculated values of absorption coefficients Ó 2009 Elsevier Ltd. All rights reserved.

Thin Solid Films, 2003

We examine several analytical models with different predictions for noise associated with conduct... more We examine several analytical models with different predictions for noise associated with conductivity fluctuations in homogeneous thin film semiconductors. In one model, the noise spectrum is assumed to reflect separately the release times of groups of trapping centres in the material. In another, the trapping time into the whole distribution of traps is assumed to dominate, predicting that, in a material like a-Si:H, where trapping into tail states is of order 1 ps, the trapping component of the noise spectrum should be unobservable. Our own analytical approach includes weak coupling between traps via the extended states, which is most clearly demonstrated by use of an R-C equivalent circuit approach for the multi-trap system. We assess the models using a Monte Carlo simulation of the trapping, generation and recombination transitions, which automatically incorporates statistical features associated with these processes, and hence it is free of assumptions. Simulation results support our thesis, and verify that the same information is contained in the real part of the modulated photoconductivity spectrum.

Journal of Nanoscience and Nanotechnology, 2012

In this paper, we report a successful growth of zinc oxide nanowire networks by simple thermal ev... more In this paper, we report a successful growth of zinc oxide nanowire networks by simple thermal evaporation process by using metallic zinc powder in the presence of oxygen. The morphological investigations of the synthesized nanowire networks are conducted by using field emission scanning electron microscopy (FESEM) which reveals that the grown products are in high-density over the whole substrate surface and possessing nanowire networks like structures. The structural and compositional properties of the grown nanowire networks are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), respectively which confirm that the synthesized products are well-crystalline, with wurtzite hexagonal phase ZnO. The as-grown ZnO nanowire networks grown on silicon substrate are utilized to fabricate n-ZnO/p-Si heterojunction diode and presented in this paper. The I-V characteristics of the fabricated heterojunction diode at different temperatures (77 K-477 K) are also investigated. High values of quality factor, which are obtained from this study, indicate a non-ideal behavior of the fabricated device. The mean barrier height of ∼0.84 eV is also estimated and presented in this paper.

Journal of Applied Physics, 2000

We show that the analysis of post-transit photocurrent i(t) to determine the energy distribution ... more We show that the analysis of post-transit photocurrent i(t) to determine the energy distribution g(E) of trapping states in a semiconductor is capable of much finer energy resolution than has hitherto been realized. Existing methods use a Laplace inversion of i(t) data to find g(E) but employ a delta function approximation for trap release times. In this article we retain the exponential distribution function for the release time and solve the rate equations directly. The analysis is performed on computer generated post-transit data for distributed and discrete traps, and compared with the earlier method and other related transform methods for determining the density of states, g(E).

Applied Physics Letters, 2013

ABSTRACT A heterojunction device was fabricated with solution processed SnS nanosheets (p-type)/T... more ABSTRACT A heterojunction device was fabricated with solution processed SnS nanosheets (p-type)/TiO2 nanoparticles (n-type) and a top Pt thin layer to form Pt/SnS/TiO2/fluorine doped tin oxide diode assembly. The SnS nanosheets were synthesized by facile hydrothermal process at low-temperature and the detailed morphological characterizations revealed that the SnS nanosheets are uniformly grown in high density. The structural characterizations confirmed the well-crystallinity and purity of the synthesized SnS nanosheets. The fabricated heterostructure device presented considerably improved electrical properties with high current of 0.78mA at 1V, reasonable ideality factor of 31 and relatively high effective barrier height of 0.634 eV.

Advanced Science Letters, 2011

This paper explores the temperature dependent heterojunction behavior of n-type zinc oxide (ZnO) ... more This paper explores the temperature dependent heterojunction behavior of n-type zinc oxide (ZnO) nanowires/p-Si diodes. The device behavior at different temperatures in forward as well as reverse biased conditions are studied and reported. From the detailed electrical properties, it is confirmed that the fabricated p-n diode showed a good stability over the temperature range of 25-130 C. The turn-on and breakdown voltage of the device slightly decreases with an increase of temperature whereas the saturation current of the device increases. The effective potential barrier height is found increasing with the increase in temperature. The quality factor is found with and without the consideration of barrier height inhomogenity. The mean potential barrier is also determined. Moreover, a value of activation energy of 53 meV which is close to the exciton binding energy of ZnO, is estimated.

MRS Proceedings, 2001

ABSTRACTWe examine different approaches to the analysis of noise in amorphous hydrogenated silico... more ABSTRACTWe examine different approaches to the analysis of noise in amorphous hydrogenated silicon associated with trapping and generation – recombination processes, which appear to predict very different noise spectra. In one approach the broad noise spectrum observed is assumed to be composed of a distribution of Lorentzian noise spectra, each associated with traps at a given energy depth, with appropriate weighting according to the energy distribution of characteristic time constants. This latter weighting is taken to mirror the energy distribution of states in the gap. This represents a linear superposition of the (weighted) contribution from individual trapping levels, each with its own characteristic time constant. This approach thus assumes that each trap level is an independent source of fluctuation in free carrier number, unaffected by the presence of other traps in the material. At first sight this assertion seems plausible, since in the multi-trapping situation envisaged,...

MRS Proceedings, 2002

We compare the predictions of several analytical models for conductivity fluctuations in a homoge... more We compare the predictions of several analytical models for conductivity fluctuations in a homogeneous semiconductor containing discrete and distributed traps, using a Monte-Carlo simulation of the relevant multi – trapping (MT) transitions. The simulation directly embodies the statistical features associated with such processes, in a simple ‘model - independent’ approach, free of approximations and assumptions. We compare the results with those of several analytical approaches. In one, the noise spectrum is assumed to reflect separately, the characteristic individual release time constants of the various trapping centers in the material. In another, the trapping time into the ensemble of electron traps is taken to be the dominant time constant, and hence, in a material such as a-Si:H, where the trapping time into tail sates is of order 1ps, this is taken to imply that this component of the conductivity noise spectrum is unobservable in practice. Our own analytical approach, incorpo...

Materials Express, 2020

In this paper, the heterojunction diode based on n-Ga doped ZnO nanowires interconnected with dis... more In this paper, the heterojunction diode based on n-Ga doped ZnO nanowires interconnected with disks/p-Si assembly was fabricated and their low-temperature electrical properties were examined. The Ga-doped ZnO nanowires interconnected with disks were grown over p-Si substrate and studied by numerous techniques to understand the structural, compositional and morphological characteristics. Electrical properties, at lowtemperatures ranging from 77 K–295 K, were examined for the fabricated heterojunction diode assembly both in reverse and forward biased conditions which exhibited an excellent stability over all the temperature range. The detailed electrical characterizations revealed that the current decreases gradually from 1.9 μA, to 0.87 μA to 0.84 μA when temperature increases from 77 K, 100 K to 150 K and then increases gradually from 1.86 μA–3.36 μA and to 9.95 μA when temperature increases from 200 K–250 K and to 295 K, respectively. Both the highest rectifying ratio at 100 K and ...

Materials Express, 2020

Heterojunction diode based on n-ZnO nanorods/p-Silicon (Si) assembly was fabricated, examined and... more Heterojunction diode based on n-ZnO nanorods/p-Silicon (Si) assembly was fabricated, examined and reported here. Horizontal quartz tube thermal evaporation technique was used for the growth of ZnO nanorods on Si substrate. The nanorods were characterized by several techniques to examine the structural, morphological, scattering and electrical properties. Wurtzite hexagonal phase of the grown aligned nanorods was observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The appearance of a sharp Raman peak at 438 cm–1 was observed and it is related to the E2(high) mode of the wurtzite hexagonal phase of ZnO. The electrical properties of the fabricated heterojunction assembly were examined at different temperatures (298∼398 K) in both reverse and forward biased conditions, and a good stability was observed over the entire temperature range. A reduction in the turn-on and breakdown voltage was observed with increasing temperature. By increasing the temperature, the...

Journal of Nanoelectronics and Optoelectronics, 2015

ABSTRACT This paper reports the successful growth of aligned ZnO nanorods on p-Si substrate via l... more ABSTRACT This paper reports the successful growth of aligned ZnO nanorods on p-Si substrate via lowtemperature simple aqueous solution process. The prepared nanorods were examined in terms of their morphological, structural, compositional and optical properties using several analytical tools such as field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and room-temperature photoluminescence (PL) spectroscopy. The detailed characterization studies revealed that the as-grown nanorods are vertically aligned, wellcrystalline possessing wurtzite hexagonal phase, grown along the [0001] direction and possessing good optical properties. Furthermore, the prepared n-ZnO nanorods/p-Si heterojunction assembly was used to fabricate heterojunction diode. The fabricated heterojunction diode exhibits good rectifying behavior of rectification factor of 16 at voltage of 7.2 volts. High values of quality factor and series resistance of the device of ∼4 and 52 kΩ, respectively, are obtained from I–V characteristics. The high series resistance may play the role of a shunt resistance that causes a partial drop in the output current of the whole assembly.

Science of Advanced Materials, 2014

ABSTRACT Well-crystalline Sn-doped ZnO nanowires were grown on p-type silicon substrates by simpl... more ABSTRACT Well-crystalline Sn-doped ZnO nanowires were grown on p-type silicon substrates by simple non-catalytic thermal evaporation process. The prepared nanowires were examined in terms of their morphological, compositional and structural properties which revealed that the as-grown nanowires are well-crystalline Sn-doped ZnO, possessing wurtzite hexagonal phase structure and grown in very high density over whole silicon substrate. Further, the as-grown n-Sn-doped ZnO nanowires were used to fabricate n-Sn-ZnO/p-Si heterojunction diode. Temperature dependant electrical properties (294–353 K and 373–433 K) of the fabricated heterojunction diode were studied in the forward and reverse bias conditions and presented in this paper. The current–voltage characteristics at varying temperature of the heterojunction diode reveal that both the quality factor and Schottky barrier height depend on temperature. However, the mean barrier height is estimated ∼1.2 eV in one attempt of analysis when a Gaussian distribution of low barrier heights is considered and found almost ∼1 eV in another attempt when the Richardson plot is linearized. Furthermore, effective barrier heights of 0.55–0.75 eV are extracted in the temperature range 294–433 K when Tung model is used. These correspond to barrier heights of 0.93–0.35 eV extracted from C–V analysis in the same range of temperatures. Although the latter results from C–V analysis exhibit closer correlation with the Schottky barrier heights extracted from I–V analysis but the discrepancy between them still exist.

Science of Advanced Materials, 2013

ABSTRACT This paper reports the facile growth, characterization and efficient heterojunction diod... more ABSTRACT This paper reports the facile growth, characterization and efficient heterojunction diode application of wellcrystalline aligned n-ZnO nanonails. The ZnO nanonails were grown on p-Silicon substrate by facile noncatalytic thermal evaporation process. Detailed morphological and structural studies revealed that the nanonails are grown in high density, possessing well-crystalline and wurtzite hexagonal phase. X-ray diffraction and Raman scattering confirm the wurtzite hexagonal phase structure whereas room-temperature photoluminescence studies affirms good optical properties for the as-grown nanonails. The as-grown aligned ZnO nanonails grown on silicon substrate are utilized to fabricate n-ZnO/p-Si heterojunction diode. The I–V characteristics of the fabricated n-ZnO/p-Si heterojunction diode are studied at temperature <300 K and ≥300 K in the forward and reverse bias conditions. By detailed studies, it was found that the junction exhibits a diode-like behavior with a value of turn-on voltage of 5 V at almost all temperatures. The rectifying behavior of the fabricated heterojunction diode, at 5 V, is demonstrated by rectifying ratio of ∼4 at 77 K which decreases to ∼2 at 277 K. Moreover, the delivered current at this turn-on voltage is the least and in the order of ∼1 �A, at 77 K. This current gradually increases to ∼6 �A which occurs, at the same turn-on voltage, when the temperature changes in the range of 77 ≤ T ≤ 277 K and drastically increases to ∼400 �A at 427 K while the rectifying ratio is dropped to ∼0.4. For the reverse-bias voltage of 5 V, the leakage current changes from ∼10−7 A at 77 K to ∼10−3 A at 477 K. These results show that the turn-on voltage, breakdown voltage and leakage current have exhibited similar behavior in reverse bias due to the increase in temperature.

MRS Proceedings, 2000

ABSTRACTWe show that the analysis of post-transit photocurrent i(t) in a multi-trapping context t... more ABSTRACTWe show that the analysis of post-transit photocurrent i(t) in a multi-trapping context to determine the density of trapping states g(E) is capable of resolving features less than kT in width. A commonly used method uses a Laplace inversion of i(t) data giving the well-known result g(E) ∼ t i(t) but employs a delta function approximation for trap release times, which results in loss of energy resolution. We show that it is possible to retain the exponential distribution function for trap release time and solve the multi-trapping rate equations directly, giving significantly improved resolution. The analysis is performed on computer generated post-transit data for distributed and discrete traps, and compared with the earlier method and other related Fourier transform methods for determining g(E). In addition, the versatility of the new method in handling cases with either distributed traps or with discrete traps means that it can be applied to disordered materials or to cryst...

Vacuum, 2009

Two sets of hydrogenated microcrystalline silicon thin-film samples were prepared by Plasma Enhan... more Two sets of hydrogenated microcrystalline silicon thin-film samples were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique at different deposition conditions of excited power and pressure. The correlation between the crystalline volume fraction for the samples determined from Raman spectra and the excited power, pressure, absorption coefficient, refractive index and optical energy gap was discussed. The values of optical parameters (refractive index and absorption coefficient), were calculated from the transmission spectra in the range 400-2500 nm. The optical band energy gap and Urbach energy were obtained using the calculated values of absorption coefficients Ó 2009 Elsevier Ltd. All rights reserved.

Thin Solid Films, 2003

We examine several analytical models with different predictions for noise associated with conduct... more We examine several analytical models with different predictions for noise associated with conductivity fluctuations in homogeneous thin film semiconductors. In one model, the noise spectrum is assumed to reflect separately the release times of groups of trapping centres in the material. In another, the trapping time into the whole distribution of traps is assumed to dominate, predicting that, in a material like a-Si:H, where trapping into tail states is of order 1 ps, the trapping component of the noise spectrum should be unobservable. Our own analytical approach includes weak coupling between traps via the extended states, which is most clearly demonstrated by use of an R-C equivalent circuit approach for the multi-trap system. We assess the models using a Monte Carlo simulation of the trapping, generation and recombination transitions, which automatically incorporates statistical features associated with these processes, and hence it is free of assumptions. Simulation results support our thesis, and verify that the same information is contained in the real part of the modulated photoconductivity spectrum.

Journal of Nanoscience and Nanotechnology, 2012

In this paper, we report a successful growth of zinc oxide nanowire networks by simple thermal ev... more In this paper, we report a successful growth of zinc oxide nanowire networks by simple thermal evaporation process by using metallic zinc powder in the presence of oxygen. The morphological investigations of the synthesized nanowire networks are conducted by using field emission scanning electron microscopy (FESEM) which reveals that the grown products are in high-density over the whole substrate surface and possessing nanowire networks like structures. The structural and compositional properties of the grown nanowire networks are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), respectively which confirm that the synthesized products are well-crystalline, with wurtzite hexagonal phase ZnO. The as-grown ZnO nanowire networks grown on silicon substrate are utilized to fabricate n-ZnO/p-Si heterojunction diode and presented in this paper. The I-V characteristics of the fabricated heterojunction diode at different temperatures (77 K-477 K) are also investigated. High values of quality factor, which are obtained from this study, indicate a non-ideal behavior of the fabricated device. The mean barrier height of ∼0.84 eV is also estimated and presented in this paper.

Journal of Applied Physics, 2000

We show that the analysis of post-transit photocurrent i(t) to determine the energy distribution ... more We show that the analysis of post-transit photocurrent i(t) to determine the energy distribution g(E) of trapping states in a semiconductor is capable of much finer energy resolution than has hitherto been realized. Existing methods use a Laplace inversion of i(t) data to find g(E) but employ a delta function approximation for trap release times. In this article we retain the exponential distribution function for the release time and solve the rate equations directly. The analysis is performed on computer generated post-transit data for distributed and discrete traps, and compared with the earlier method and other related transform methods for determining the density of states, g(E).

Applied Physics Letters, 2013

ABSTRACT A heterojunction device was fabricated with solution processed SnS nanosheets (p-type)/T... more ABSTRACT A heterojunction device was fabricated with solution processed SnS nanosheets (p-type)/TiO2 nanoparticles (n-type) and a top Pt thin layer to form Pt/SnS/TiO2/fluorine doped tin oxide diode assembly. The SnS nanosheets were synthesized by facile hydrothermal process at low-temperature and the detailed morphological characterizations revealed that the SnS nanosheets are uniformly grown in high density. The structural characterizations confirmed the well-crystallinity and purity of the synthesized SnS nanosheets. The fabricated heterostructure device presented considerably improved electrical properties with high current of 0.78mA at 1V, reasonable ideality factor of 31 and relatively high effective barrier height of 0.634 eV.

Advanced Science Letters, 2011

This paper explores the temperature dependent heterojunction behavior of n-type zinc oxide (ZnO) ... more This paper explores the temperature dependent heterojunction behavior of n-type zinc oxide (ZnO) nanowires/p-Si diodes. The device behavior at different temperatures in forward as well as reverse biased conditions are studied and reported. From the detailed electrical properties, it is confirmed that the fabricated p-n diode showed a good stability over the temperature range of 25-130 C. The turn-on and breakdown voltage of the device slightly decreases with an increase of temperature whereas the saturation current of the device increases. The effective potential barrier height is found increasing with the increase in temperature. The quality factor is found with and without the consideration of barrier height inhomogenity. The mean potential barrier is also determined. Moreover, a value of activation energy of 53 meV which is close to the exciton binding energy of ZnO, is estimated.

MRS Proceedings, 2001

ABSTRACTWe examine different approaches to the analysis of noise in amorphous hydrogenated silico... more ABSTRACTWe examine different approaches to the analysis of noise in amorphous hydrogenated silicon associated with trapping and generation – recombination processes, which appear to predict very different noise spectra. In one approach the broad noise spectrum observed is assumed to be composed of a distribution of Lorentzian noise spectra, each associated with traps at a given energy depth, with appropriate weighting according to the energy distribution of characteristic time constants. This latter weighting is taken to mirror the energy distribution of states in the gap. This represents a linear superposition of the (weighted) contribution from individual trapping levels, each with its own characteristic time constant. This approach thus assumes that each trap level is an independent source of fluctuation in free carrier number, unaffected by the presence of other traps in the material. At first sight this assertion seems plausible, since in the multi-trapping situation envisaged,...