Rubi Gul - Academia.edu (original) (raw)
Papers by Rubi Gul
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018
Crystals
CdTe:Cl doped single crystals were grown under conditions of tellurium excess by using an acceler... more CdTe:Cl doped single crystals were grown under conditions of tellurium excess by using an accelerated crucible rotation technique, modified vertical Bridgman (ACRT-MVB) method. Chlorine dopant levels were kept at 4.4 × 1019 at·cm−3, for all growths, while the Te excess level varied from 3.5 to 15% by weight. The relationship between the detector performance, Te inclusions, and resistivity was investigated in detail. Tellurium excess caused additional nucleation which decreased the average single crystal grain size. At the same time, the increasing Te excess level improved the electrical transport properties. In the three Cl-doped, and one In-doped CdTe crystals, detectors from Cl-doped CdTe grown under 15% Te excess showed better response to gammas and alphas, and high µτ for electrons (1.8 × 10−3 cm2/V), as well as for holes (5.1 × 10−4 cm2/V). The full-width half maximum for the Cl-doped CdTe were very large, as the peaks were broadened, especially at high bias. This could be due ...
2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), 2016
Surface passivation and contact deposition are important processes in the fabrication of cadmium ... more Surface passivation and contact deposition are important processes in the fabrication of cadmium zinc telluride (CdZnTe) X-rays and gamma-rays detectors. Surface passivation is used to reduce the effects of fabrication-induced surface defects. It is also used to reduce defects that could result from aging of the detector. Another important factor in charge collection is the interface between the electrical contacts and the detector wafer. In this paper, we present the results of the effects of chemo-mechanically polishing CdZnTe wafers with a hydrogen bromide in hydrogen peroxide solution followed by passivation in a mixture of potassium hydroxide in hydrogen peroxide solution by monitoring their energy resolutions over a 4-day period. The results showed that the 59.5-keV gamma peak of Am-241 remains under the same channel over the 4 days.
IEEE Transactions on Nuclear Science, 2017
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2010
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2009
The aim of this study is the evaluation of radiation effects in detectors based on p-type MCZmagn... more The aim of this study is the evaluation of radiation effects in detectors based on p-type MCZmagnetic czochralski (MCz) Si that was converted to n-type by thermal donor (TD) introduction. As-processed p+-p-n+ detectors were annealed at 430° C resulting in p+-n ( ...
2011 IEEE Nuclear Science Symposium Conference Record, 2011
CdZnTe (CZT) and CdMnTe (CMT) materials come into the spotlight for room-temperature semiconducto... more CdZnTe (CZT) and CdMnTe (CMT) materials come into the spotlight for room-temperature semiconductor detectors. Nonethelss, both materials still have limitations for the production of economical, uniform, and large-volume devices due to the zinc (Zn) segregation in CZT and manganese purity in CMT. The effective segregation coefficient of Zn in the CdTe host is nearly 1.3, so about 5–6% of Zn
IEEE Transactions on Nuclear Science, 2012
ABSTRACT Although CdZnTe (CZT) and CdMnTe (CMT) materials are leading contenders for room-tempera... more ABSTRACT Although CdZnTe (CZT) and CdMnTe (CMT) materials are leading contenders for room-temperature semiconductor detectors, nonetheless, both materials have limitations hindering their full usage in producing economical, uniform, large-volume devices due to their grain/twin boundaries, material purity, secondary-phase Te defects and material segregation. We tried to prevent the generation of twin and subgrain boundaries to achieve large-volume CZT crystals by means of local temperature control between the CZT melt and quartz crucible. Also, we have expanded the understanding of the electrical and structural properties of coherent/incoherent twin boundaries. The high residual impurities in the starting source materials, especially in manganese, were identified as obstacles against obtaining high-performance CMT detectors. We found that purifying manganese telluride (MnTe) via a floating Te melt-zone very effectively removes impurities, leading to better detectors. CMT detectors fabricated with purified material give a 2.1% energy resolution for 662 keV with a 137^{137}137Cs gamma source without any electron-loss corrections. Secondary-phase Te defects deteriorate detector performance due to incomplete charge collection caused by charge trapping. In situ growth interface studies reveal the thermo-migration of Te inclusions to CZT melts and the dependence of Te-inclusion size on the cooling rate. The effective segregation coefficient of Zn in the CdTe host is nearly 1.3, so about 5%–6% of Zn deviation was reported in Bridgman-grown CZT (Zn$,=$10% ingots. Such uncontrolled Zn variations cause a significant variation of the band-gap throughout the ingot and, consequently, affect the nonuniformity of the detectors' responses. Practically, this means that manufacturers cannot cut the ingot parallel to the crystal growth direction. We also de- onstrated that the segregation of Zn can be controlled by creating particular thermal environments after growth.
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIX, 2017
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIX, 2017
Temperature dependence of thermal transport properties
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIX, 2017
High-resolution position-sensing has been proposed to correct response non-uniformities in Cadmiu... more High-resolution position-sensing has been proposed to correct response non-uniformities in Cadmium Zinc Telluride (CZT) gamma ray detectors by virtually subdividing the area into small voxels and equalizing responses from each voxel. 3D pixelated detectors coupled with multichannel readout electronics are the most advanced type of CZT devices offering many options in signal processing and enhancing detector performance. The main hurdle in achieving high sub-pixel position resolution is the relatively low signal induced on the neighboring pixels because of the electrostatic shielding effect caused by the collecting pixel. In addition, to achieve high position sensitivity one should rely on time-correlated transient signals, which means that digitized output signals must be used. Previous results have shown the benefit of using a focused laser beam to study position resolution in 3D pixelated detectors. We present the results of our studies to measure the amplitude of the pixel signals so that these can be used to measure positions of the interaction points. This is done with the processing of digitized correlated time signals measured from several adjacent pixels taking into account rise-time and charge-sharing effects. In these measurements we used a focused pulsed laser to generate a 10-micron beam at one milliwatt (650-nm wavelength) over the detector surface while the collecting pixel was moved in cardinal directions. The results include measurements that present the benefits of combining conventional pixel geometry with digital pulse processing for the best approach in achieving sub-pixel position resolution with different pixel dimensions ranging from 0.5 mm to 1.72 mm.
2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), 2016
Cadmium zinc telluride (CdZnTe) X-rays and gamma-rays detectors have found applications in radiol... more Cadmium zinc telluride (CdZnTe) X-rays and gamma-rays detectors have found applications in radiological and nuclear security, environmental protection, astrophysics, and nuclear medical imaging. Cadmium manganese telluride (CdMnTe) has the potential for similar success as CdZnTe in the detection of ionizing radiations. The detection of radiological and nuclear threats would greatly benefit from detector wafers with large-volume, high-performance, and low-cost of production. This paper presents recent advances in the development of CdZnTe and CdMnTe nuclear detectors with the focus on the detection of radiological and nuclear threats. Efforts on improving the performance of CdZnTe and CdMnTe detectors were made in three major areas: crystal growth, post-growth annealing, and device fabrication. In crystal growth, we optimized ampoule carbon coating for CdZnTe and eliminated detector performance-limiting secondary phase particles in CdMnTe. In post-growth annealing of CdMnTe and CdZnT...
Enormous effort has been exerted on research and development of CdZnTe (CZT) over the past two de... more Enormous effort has been exerted on research and development of CdZnTe (CZT) over the past two decades, as well as the pursuit of an alternative material to mitigate the disadvantages in today’s CZT material or provide comparable device performance at a lower cost of production. Although the quality of CdZnTe crystals has been improved drastically over the past few years and the material cost has steadily decreased, the yield of large-volume high-quality detector-grade CZT continues to be an issue due to its poor thermo-physical properties. TlBr was found to be a promising material to compete with CZT, but the contact degradation and device stability are still big issues and severely hinder the deployment of commercial TlBr-based devices for nonproliferation and national security applications. At BNL, we are developing a new compound Cd1-xZnx Te1-y Sey (CZTS) that holds promise as a potentially viable crystal for the replacement of CZT for some radiation detection and imaging applic...
2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2017
Cadmium zinc telluride (CdZnTe) radiation detectors have found applications in medical imaging an... more Cadmium zinc telluride (CdZnTe) radiation detectors have found applications in medical imaging and in the detection of radiological and nuclear threats. While there has been success in developing CdZnTe detectors with less than 1% FWHM energy resolution at the 662 keV gamma energy, charge collection can be improved through optimization of surface treatment techniques. The dominant surface species on CdZnTe are cadmium, tellurium, and tellurium oxide. The tellurium oxide is expected to produce a more chemically stable surface. This paper presents the quantification of the tellurium oxide species on CdZnTe wafers that are freshly etched in a mixture of hydrogen bromide in hydrogen peroxide and ethylene glycol solution. It also presents the effects of the tellurium oxide on surface current and detector performance. X-ray photoelectron spectroscopy (XPS) was used to quantify the tellurium oxide species on the wafer surface. The formation of tellurium oxide on the CdZnTe wafers immediate...
American Journal of Materials Science, 2015
Chemical etching and chemo-mechanical polishing are techniques used to remove surface defects and... more Chemical etching and chemo-mechanical polishing are techniques used to remove surface defects and damages caused by cutting and mechanical polishing of cadmium zinc telluride (CdZnTe) nuclear detector materials. Etching and chemo-mechanical polishing processes often form thin films on the surfaces of the CdZnTe wafers. While several studies have been done on etching and chemo-mechanical polishing using different chemicals, there is a lack of reporting on the uses of the same chemical solution to study the effects of these two-surface processing techniques. This paper focuses on comparing the effects of chemical etching and chemo-mechanical polishing on the electrical properties of CdZnTe detectors using the same chemical solution: bromine-methanol-ethylene glycol. Three CdZnTe samples were cut from the same region of the ingot, mechanically polished, and used to studying the two surface processing techniques. The current-voltage experiments on the samples gave a measured bulk resist...
Journal of Electronic Materials, 2015
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018
Crystals
CdTe:Cl doped single crystals were grown under conditions of tellurium excess by using an acceler... more CdTe:Cl doped single crystals were grown under conditions of tellurium excess by using an accelerated crucible rotation technique, modified vertical Bridgman (ACRT-MVB) method. Chlorine dopant levels were kept at 4.4 × 1019 at·cm−3, for all growths, while the Te excess level varied from 3.5 to 15% by weight. The relationship between the detector performance, Te inclusions, and resistivity was investigated in detail. Tellurium excess caused additional nucleation which decreased the average single crystal grain size. At the same time, the increasing Te excess level improved the electrical transport properties. In the three Cl-doped, and one In-doped CdTe crystals, detectors from Cl-doped CdTe grown under 15% Te excess showed better response to gammas and alphas, and high µτ for electrons (1.8 × 10−3 cm2/V), as well as for holes (5.1 × 10−4 cm2/V). The full-width half maximum for the Cl-doped CdTe were very large, as the peaks were broadened, especially at high bias. This could be due ...
2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), 2016
Surface passivation and contact deposition are important processes in the fabrication of cadmium ... more Surface passivation and contact deposition are important processes in the fabrication of cadmium zinc telluride (CdZnTe) X-rays and gamma-rays detectors. Surface passivation is used to reduce the effects of fabrication-induced surface defects. It is also used to reduce defects that could result from aging of the detector. Another important factor in charge collection is the interface between the electrical contacts and the detector wafer. In this paper, we present the results of the effects of chemo-mechanically polishing CdZnTe wafers with a hydrogen bromide in hydrogen peroxide solution followed by passivation in a mixture of potassium hydroxide in hydrogen peroxide solution by monitoring their energy resolutions over a 4-day period. The results showed that the 59.5-keV gamma peak of Am-241 remains under the same channel over the 4 days.
IEEE Transactions on Nuclear Science, 2017
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2010
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2009
The aim of this study is the evaluation of radiation effects in detectors based on p-type MCZmagn... more The aim of this study is the evaluation of radiation effects in detectors based on p-type MCZmagnetic czochralski (MCz) Si that was converted to n-type by thermal donor (TD) introduction. As-processed p+-p-n+ detectors were annealed at 430° C resulting in p+-n ( ...
2011 IEEE Nuclear Science Symposium Conference Record, 2011
CdZnTe (CZT) and CdMnTe (CMT) materials come into the spotlight for room-temperature semiconducto... more CdZnTe (CZT) and CdMnTe (CMT) materials come into the spotlight for room-temperature semiconductor detectors. Nonethelss, both materials still have limitations for the production of economical, uniform, and large-volume devices due to the zinc (Zn) segregation in CZT and manganese purity in CMT. The effective segregation coefficient of Zn in the CdTe host is nearly 1.3, so about 5–6% of Zn
IEEE Transactions on Nuclear Science, 2012
ABSTRACT Although CdZnTe (CZT) and CdMnTe (CMT) materials are leading contenders for room-tempera... more ABSTRACT Although CdZnTe (CZT) and CdMnTe (CMT) materials are leading contenders for room-temperature semiconductor detectors, nonetheless, both materials have limitations hindering their full usage in producing economical, uniform, large-volume devices due to their grain/twin boundaries, material purity, secondary-phase Te defects and material segregation. We tried to prevent the generation of twin and subgrain boundaries to achieve large-volume CZT crystals by means of local temperature control between the CZT melt and quartz crucible. Also, we have expanded the understanding of the electrical and structural properties of coherent/incoherent twin boundaries. The high residual impurities in the starting source materials, especially in manganese, were identified as obstacles against obtaining high-performance CMT detectors. We found that purifying manganese telluride (MnTe) via a floating Te melt-zone very effectively removes impurities, leading to better detectors. CMT detectors fabricated with purified material give a 2.1% energy resolution for 662 keV with a 137^{137}137Cs gamma source without any electron-loss corrections. Secondary-phase Te defects deteriorate detector performance due to incomplete charge collection caused by charge trapping. In situ growth interface studies reveal the thermo-migration of Te inclusions to CZT melts and the dependence of Te-inclusion size on the cooling rate. The effective segregation coefficient of Zn in the CdTe host is nearly 1.3, so about 5%–6% of Zn deviation was reported in Bridgman-grown CZT (Zn$,=$10% ingots. Such uncontrolled Zn variations cause a significant variation of the band-gap throughout the ingot and, consequently, affect the nonuniformity of the detectors' responses. Practically, this means that manufacturers cannot cut the ingot parallel to the crystal growth direction. We also de- onstrated that the segregation of Zn can be controlled by creating particular thermal environments after growth.
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIX, 2017
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIX, 2017
Temperature dependence of thermal transport properties
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIX, 2017
High-resolution position-sensing has been proposed to correct response non-uniformities in Cadmiu... more High-resolution position-sensing has been proposed to correct response non-uniformities in Cadmium Zinc Telluride (CZT) gamma ray detectors by virtually subdividing the area into small voxels and equalizing responses from each voxel. 3D pixelated detectors coupled with multichannel readout electronics are the most advanced type of CZT devices offering many options in signal processing and enhancing detector performance. The main hurdle in achieving high sub-pixel position resolution is the relatively low signal induced on the neighboring pixels because of the electrostatic shielding effect caused by the collecting pixel. In addition, to achieve high position sensitivity one should rely on time-correlated transient signals, which means that digitized output signals must be used. Previous results have shown the benefit of using a focused laser beam to study position resolution in 3D pixelated detectors. We present the results of our studies to measure the amplitude of the pixel signals so that these can be used to measure positions of the interaction points. This is done with the processing of digitized correlated time signals measured from several adjacent pixels taking into account rise-time and charge-sharing effects. In these measurements we used a focused pulsed laser to generate a 10-micron beam at one milliwatt (650-nm wavelength) over the detector surface while the collecting pixel was moved in cardinal directions. The results include measurements that present the benefits of combining conventional pixel geometry with digital pulse processing for the best approach in achieving sub-pixel position resolution with different pixel dimensions ranging from 0.5 mm to 1.72 mm.
2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), 2016
Cadmium zinc telluride (CdZnTe) X-rays and gamma-rays detectors have found applications in radiol... more Cadmium zinc telluride (CdZnTe) X-rays and gamma-rays detectors have found applications in radiological and nuclear security, environmental protection, astrophysics, and nuclear medical imaging. Cadmium manganese telluride (CdMnTe) has the potential for similar success as CdZnTe in the detection of ionizing radiations. The detection of radiological and nuclear threats would greatly benefit from detector wafers with large-volume, high-performance, and low-cost of production. This paper presents recent advances in the development of CdZnTe and CdMnTe nuclear detectors with the focus on the detection of radiological and nuclear threats. Efforts on improving the performance of CdZnTe and CdMnTe detectors were made in three major areas: crystal growth, post-growth annealing, and device fabrication. In crystal growth, we optimized ampoule carbon coating for CdZnTe and eliminated detector performance-limiting secondary phase particles in CdMnTe. In post-growth annealing of CdMnTe and CdZnT...
Enormous effort has been exerted on research and development of CdZnTe (CZT) over the past two de... more Enormous effort has been exerted on research and development of CdZnTe (CZT) over the past two decades, as well as the pursuit of an alternative material to mitigate the disadvantages in today’s CZT material or provide comparable device performance at a lower cost of production. Although the quality of CdZnTe crystals has been improved drastically over the past few years and the material cost has steadily decreased, the yield of large-volume high-quality detector-grade CZT continues to be an issue due to its poor thermo-physical properties. TlBr was found to be a promising material to compete with CZT, but the contact degradation and device stability are still big issues and severely hinder the deployment of commercial TlBr-based devices for nonproliferation and national security applications. At BNL, we are developing a new compound Cd1-xZnx Te1-y Sey (CZTS) that holds promise as a potentially viable crystal for the replacement of CZT for some radiation detection and imaging applic...
2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2017
Cadmium zinc telluride (CdZnTe) radiation detectors have found applications in medical imaging an... more Cadmium zinc telluride (CdZnTe) radiation detectors have found applications in medical imaging and in the detection of radiological and nuclear threats. While there has been success in developing CdZnTe detectors with less than 1% FWHM energy resolution at the 662 keV gamma energy, charge collection can be improved through optimization of surface treatment techniques. The dominant surface species on CdZnTe are cadmium, tellurium, and tellurium oxide. The tellurium oxide is expected to produce a more chemically stable surface. This paper presents the quantification of the tellurium oxide species on CdZnTe wafers that are freshly etched in a mixture of hydrogen bromide in hydrogen peroxide and ethylene glycol solution. It also presents the effects of the tellurium oxide on surface current and detector performance. X-ray photoelectron spectroscopy (XPS) was used to quantify the tellurium oxide species on the wafer surface. The formation of tellurium oxide on the CdZnTe wafers immediate...
American Journal of Materials Science, 2015
Chemical etching and chemo-mechanical polishing are techniques used to remove surface defects and... more Chemical etching and chemo-mechanical polishing are techniques used to remove surface defects and damages caused by cutting and mechanical polishing of cadmium zinc telluride (CdZnTe) nuclear detector materials. Etching and chemo-mechanical polishing processes often form thin films on the surfaces of the CdZnTe wafers. While several studies have been done on etching and chemo-mechanical polishing using different chemicals, there is a lack of reporting on the uses of the same chemical solution to study the effects of these two-surface processing techniques. This paper focuses on comparing the effects of chemical etching and chemo-mechanical polishing on the electrical properties of CdZnTe detectors using the same chemical solution: bromine-methanol-ethylene glycol. Three CdZnTe samples were cut from the same region of the ingot, mechanically polished, and used to studying the two surface processing techniques. The current-voltage experiments on the samples gave a measured bulk resist...
Journal of Electronic Materials, 2015