An oxygen-related defect was studied in nominally undoped CdTe crystals grown by the high pressur... more An oxygen-related defect was studied in nominally undoped CdTe crystals grown by the high pressure Bridgman technique using thermo-electrical effect spectroscopy and first-principles band structure calculations. Based on the linear relationship between the oxygen concentration and the emitted charge from the defect level with an ionization energy E=0.184±0.011 eV and a capture cross section sigma=(7±4)×10-17 cm2 we show that the defect is an oxygen complex. Using thermal annealing experiments we show that the defect complex contains cadmium vacancies. Using first-principles band structure calculations we assign the defect level to the second ionization level of the isoelectronic oxygen-cadmium vacancy pair (OTe-VCd)-/2-.
A special CdZnTe (CZT) device on THM grown crystal has been developed. The device has different w... more A special CdZnTe (CZT) device on THM grown crystal has been developed. The device has different work function metals on opposite electrodes yet operates at room temperature like a conventional back-to-back symmetric MSM detector and not a one directional Schottky diode device. Aiming at creating a big breakthrough in CZT imaging device technology, the special CZT device presented in this
ABSTRACT The focus of this paper is to investigate, experimentally and theoretical, the optimum o... more ABSTRACT The focus of this paper is to investigate, experimentally and theoretical, the optimum operating bias, in cadmium zinc telluride Cd 0.9Zn0.1Te (CZT) crystals grown using the traveling heater method (THM), required to achieve maximum energy resolution. It was found that 5 mm thick detectors that have low electron trapping, (μτ)e≥1×10−2 cm2/V, operates efficiently at relatively low applied bias, 200 V; while detectors with high electron trapping, (μτ)e≤5×10−3 cm2/V, required relative high voltage: as high as 1000 V for 5 mm thick detectors. Similarly 10 mm thick detectors can be operated at as low as 500 V. Moreover, both charge collection efficiency (CCE) and energy resolution(ER) were found to follow the same trend.
Proceedings of Spie the International Society For Optical Engineering, 2001
Thermoelectric Effect Spectroscopy and Thermally Stimulated Current measurements were used to inv... more Thermoelectric Effect Spectroscopy and Thermally Stimulated Current measurements were used to investigate trapping levels in semi-insulating CdTe and Cd 1-x Zn x Te crystals from multiple ingots grown by vertical Bridgman with over pressure control and high-pressure Bridgman methods. The crystals from different growth methods have different dislocation densities as well as Zn concentrations. The thermal ionization energies of these levels were extracted using both the variable heating rate and initial rise methods; the trapping cross sections were then calculated using the temperature maximum method. We report here that the shallow levels observed at E 1 =0.11±0.02 and E 2 =0.17±0.02 eV are intrinsic and the latter level is most likely related to the dislocation density.
Good uniformity in electron transport has been observed on Cd0.9Zn0.1Te crystals grown by the Tra... more Good uniformity in electron transport has been observed on Cd0.9Zn0.1Te crystals grown by the Traveling Heater Method (THM) using alpha-particle measurements. Excellent electron mobility-lifetime products have been measured consistently on the order of 1times 10-2 cm2/V. A coplanar-grid detector of size 10times10times5 mm3 has been fabricated from this material, and it shows an energy resolution of 2.1% FWHM at room
Proquest Dissertations and Theses Thesis Washington State University 2003 Publication Number Aai3110846 Isbn 9780496583805 Source Dissertation Abstracts International Volume 64 11 Section B Page 5713 113 P, 2003
Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have bee... more Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have been investigated using thermally stimulated spectroscopy with the general aim of identifying and then understanding the effects of the defects on the electrical and optical properties of these compounds. In order to identify and understand the effects of these defects (trapping levels), the samples were subjected to room temperature deformation, high temperature annealing, and dopants diffusion. The samples were always analyzed before and after any process. It is found that the trapping levels observed at ˜61 K and ˜114 K with thermal ionization energies of 0.12 +/- 0.01 eV and 0.23 +/- 0.01 eV and trapping cross-sections of 4.7 x 10-16 and 7.8 x 10-17 cm2 are associated with the isolated first and second ionized state of the cadmium vacancy, while trapping levels observed at ˜51 K and ˜94 K with thermal ionization energies of 0.09 +/- 0.01 eV and 0.18 +/- 0.01 eV and trapping cross-sections of 9.3 x 10 -17 and 6.8 x 10-17 cm2 are associated with first and second states of the isoelectronic oxygen-cadmium vacancy complex (VCd-OTe) respectively. In addition, we found that deep level trapping states located near the middle of the band gap (in the region between 230 K and 267 K) in undoped as grown CdTe are related to the tellurium antisite-cadmium vacancy complex (TeCd-V Cd) where the lowest thermal ionization state is 0.78 +/- 0.01 eV. The thermal ionization energies (transition energies) were extracted using variable heating rate and/or initial rise methods. Our results have been reinforced with theoretical calculations using linearized augmented plane wave (LAPW) within the local density approximation (LDA). Also, from our room temperature deformation, we have found evidence of three levels of dislocation defects in CdTe crystals. The first two energy levels, with ionization energies of E1 = 0.06 +/- 0.01 eV and E2 = 0.38 +/- 0.01 eV are due to Cd dislocations. The third deeper level, with ionization energy of E3 = 0.49 +/- 0.01 eV, is related to Te dislocations. In addition, we have found that the intensity of the induced dislocations, photoconductivity, and resistivity of the crystals are proportional to the deformation rate and the direction of the applied compression load. The annealing result showed that the applied load did not reach the yield point of the crystals; therefore, the induced deformation is elastic.
The excellent room temperature spectral performance of cadmium zinc telluride detectors grown via... more The excellent room temperature spectral performance of cadmium zinc telluride detectors grown via the Traveling Heater Method (THM) makes this approach suitable for the mass deployment of radiation detectors for applications in homeland security and medical imaging. This paper reports our progress in fabricating thicker and larger area detectors from THM grown CZT. We discuss the performance of such 20x20x10 mm 3, and 10x10x10 mm 3 monolithic pixellated detectors and virtual Frisch-Grid 4x4x12 mm3 devices, and describe the various physical properties of the materials.
High-performance semi-insulating single crystals of n-type Cd 0 9 Zn 0 1 Te (CZT) were grown usin... more High-performance semi-insulating single crystals of n-type Cd 0 9 Zn 0 1 Te (CZT) were grown using the traveling heater method (THM). X-ray and -ray detector configurations fabricated from this material have a room-temperature mean energy resolution of 4.3% FWHM for a 57 Co source (122 keV) and uniform pixel-to-pixel response on monolithic 20 20 5 mm 3 pixellated detectors. Energy resolution of 1% FWHM for 137 Cs (662 keV) has been measured on virtual Frisch-grid 4 4 11 mm 3 devices useful for homeland security applications. Additional characterization techniques including mobility-lifetime measurements, infrared microscopy, X-ray topography, and OPTICAL Deep Level Transient Spectroscopy (ODLTS) have demonstrated the superior quality of this THM CZT.
The spectral response of several crystals grown by the Traveling Heater Method (THM) were investi... more The spectral response of several crystals grown by the Traveling Heater Method (THM) were investigated. An energy resolution of 0.98% for a Pseudo Frisch-Grid of 4 4 9 mm 3 and 2.1% FWHM for a coplanar-grid of size 11 11 5 mm 3 were measured using 137 Cs-662 keV. In addition a 4% FWHM at 122 keV has also been measured on 20 20 5 mm 3 monolithic pixellated devices. The material shows great potential toward producing large-volume detectors with spectral performance that meets the requirement for high-resolution gamma-ray spectroscopy.
New results on the effects of small-scale defects on the charge-carrier transport in singlecrysta... more New results on the effects of small-scale defects on the charge-carrier transport in singlecrystal CdZnTe (CZT) material were produced. We conducted detailed studies of the role of Te inclusions in CZT by employing a highty collimated synchrotron x-ray radiation source available at Brookhaven's National Synchrotron Light Source (NSLS). We were able to induce polarization effects by irradiating specific areas with the detector. These measurements allowed the first quantitative comparison between areas that are free of Te inclusions and those with a relatively high concentration of inclusions. The results of these polarbtion studies will be reported.
High-quality large single crystals of Cd0.9Zn0.1Te (> 7 inch3) have been consistently produced by... more High-quality large single crystals of Cd0.9Zn0.1Te (> 7 inch3) have been consistently produced by the THM (solution growth) method. Various large-volume X-ray and gamma-ray detector configurations fabricated from this THM CZT material have produced detectors with excellent performance. A room-temperature mean energy resolution of 4.3% for a Co-57 source (122 keV) and uniform pixel-to-pixel response have been demonstrated on monolithic 20times20times5 mm3 pixellated detectors useful for imaging applications. In addition, energy resolution of <1% FWHM @ Cs-137 (662 keV) has been measured on virtual Frisch-Grid 4times4times11 mm3 devices useful for homeland security applications. Additional characterization techniques such as mu-tau measurements, infrared microscopy, X-ray topography and ODLTS have demonstrated the superior quality of this THM CZT. The results of material characterization measurements and detector tests will be presented.
Long term reliability is critical for a detector module to be used in applications that can not a... more Long term reliability is critical for a detector module to be used in applications that can not afford failure and require high accuracy such as medical imaging and homeland security. In this study, we report the reliability of pixellated Cadmium Zinc Telluride (CZT) detector modules fabricated from crystals grown by the Traveling Heater Method (THM). The reliability of the module which consists of the pixellated detector assembled to a PCB carrier board via conductive epoxy was studied with both a Quantitative Accelerated Life Test (QALT) as well as the Highly Accelerated Stress Test (HAST) which is a common form of a Qualitative Accelerated Life test. The robustness of the THM pixellated CZT detector modules is demonstrated via the pre- and post- accelerated life test comparison of the leakage current and the spectral performance of the assembled module. A shear test was also used to ensure the adhesion strength of the epoxy bonded method. To our knowledge, this type of study on pixellated CZT detector module has been very rare if not the first of its kind.
This work focuses on the thickness scalability of traveling heater method (THM) grown CdZnTe crys... more This work focuses on the thickness scalability of traveling heater method (THM) grown CdZnTe crystals to produce large volume detectors with optimized spectroscopic performance. To meet this challenge, we have tuned both our THM growth process, to grow 75 mm diameter ingots, and our postgrowth annealing process. We have increased the thickness of our sliced wafers from 6 to 12 and 18 mm allowing the production of 10 and 15 mm thick detectors. As the detectors' thickness is scaled up, the energy resolution of both types, as pseudo-Frisch grid and pixelated monolithic detectors showed no degradation indicating improved materials uniformity and transport properties.
Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have bee... more Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have been investigated using thermally stimulated spectroscopy with the general aim of identifying and then understanding the effects of the defects on the electrical and optical properties of these compounds. In order to identify and understand the effects of these defects (trapping levels), the samples were subjected to room temperature deformation, high temperature annealing, and dopants diffusion. The samples were always analyzed before and after any process. It is found that the trapping levels observed at ˜61 K and ˜114 K with thermal ionization energies of 0.12 +/- 0.01 eV and 0.23 +/- 0.01 eV and trapping cross-sections of 4.7 x 10-16 and 7.8 x 10-17 cm2 are associated with the isolated first and second ionized state of the cadmium vacancy, while trapping levels observed at ˜51 K and ˜94 K with thermal ionization energies of 0.09 +/- 0.01 eV and 0.18 +/- 0.01 eV and trapping cross-sections of 9.3 x 10 -17 and 6.8 x 10-17 cm2 are associated with first and second states of the isoelectronic oxygen-cadmium vacancy complex (VCd-OTe) respectively. In addition, we found that deep level trapping states located near the middle of the band gap (in the region between 230 K and 267 K) in undoped as grown CdTe are related to the tellurium antisite-cadmium vacancy complex (TeCd-V Cd) where the lowest thermal ionization state is 0.78 +/- 0.01 eV. The thermal ionization energies (transition energies) were extracted using variable heating rate and/or initial rise methods. Our results have been reinforced with theoretical calculations using linearized augmented plane wave (LAPW) within the local density approximation (LDA). Also, from our room temperature deformation, we have found evidence of three levels of dislocation defects in CdTe crystals. The first two energy levels, with ionization energies of E1 = 0.06 +/- 0.01 eV and E2 = 0.38 +/- 0.01 eV are due to Cd dislocations. The third deeper level, with ionization energy of E3 = 0.49 +/- 0.01 eV, is related to Te dislocations. In addition, we have found that the intensity of the induced dislocations, photoconductivity, and resistivity of the crystals are proportional to the deformation rate and the direction of the applied compression load. The annealing result showed that the applied load did not reach the yield point of the crystals; therefore, the induced deformation is elastic.
... 7±4)10−17 cm2, respectively. In this paper we study the behavior of the isoelectronic oxygen-... more ... 7±4)10−17 cm2, respectively. In this paper we study the behavior of the isoelectronic oxygen-cation vacancy pair (OTe–VCd/Zn) in CdZnTe using TEES and first-principles total-energy calculations. We find that adding Zn to ...
An oxygen-related defect was studied in nominally undoped CdTe crystals grown by the high pressur... more An oxygen-related defect was studied in nominally undoped CdTe crystals grown by the high pressure Bridgman technique using thermo-electrical effect spectroscopy and first-principles band structure calculations. Based on the linear relationship between the oxygen concentration and the emitted charge from the defect level with an ionization energy E=0.184±0.011 eV and a capture cross section sigma=(7±4)×10-17 cm2 we show that the defect is an oxygen complex. Using thermal annealing experiments we show that the defect complex contains cadmium vacancies. Using first-principles band structure calculations we assign the defect level to the second ionization level of the isoelectronic oxygen-cadmium vacancy pair (OTe-VCd)-/2-.
A special CdZnTe (CZT) device on THM grown crystal has been developed. The device has different w... more A special CdZnTe (CZT) device on THM grown crystal has been developed. The device has different work function metals on opposite electrodes yet operates at room temperature like a conventional back-to-back symmetric MSM detector and not a one directional Schottky diode device. Aiming at creating a big breakthrough in CZT imaging device technology, the special CZT device presented in this
ABSTRACT The focus of this paper is to investigate, experimentally and theoretical, the optimum o... more ABSTRACT The focus of this paper is to investigate, experimentally and theoretical, the optimum operating bias, in cadmium zinc telluride Cd 0.9Zn0.1Te (CZT) crystals grown using the traveling heater method (THM), required to achieve maximum energy resolution. It was found that 5 mm thick detectors that have low electron trapping, (μτ)e≥1×10−2 cm2/V, operates efficiently at relatively low applied bias, 200 V; while detectors with high electron trapping, (μτ)e≤5×10−3 cm2/V, required relative high voltage: as high as 1000 V for 5 mm thick detectors. Similarly 10 mm thick detectors can be operated at as low as 500 V. Moreover, both charge collection efficiency (CCE) and energy resolution(ER) were found to follow the same trend.
Proceedings of Spie the International Society For Optical Engineering, 2001
Thermoelectric Effect Spectroscopy and Thermally Stimulated Current measurements were used to inv... more Thermoelectric Effect Spectroscopy and Thermally Stimulated Current measurements were used to investigate trapping levels in semi-insulating CdTe and Cd 1-x Zn x Te crystals from multiple ingots grown by vertical Bridgman with over pressure control and high-pressure Bridgman methods. The crystals from different growth methods have different dislocation densities as well as Zn concentrations. The thermal ionization energies of these levels were extracted using both the variable heating rate and initial rise methods; the trapping cross sections were then calculated using the temperature maximum method. We report here that the shallow levels observed at E 1 =0.11±0.02 and E 2 =0.17±0.02 eV are intrinsic and the latter level is most likely related to the dislocation density.
Good uniformity in electron transport has been observed on Cd0.9Zn0.1Te crystals grown by the Tra... more Good uniformity in electron transport has been observed on Cd0.9Zn0.1Te crystals grown by the Traveling Heater Method (THM) using alpha-particle measurements. Excellent electron mobility-lifetime products have been measured consistently on the order of 1times 10-2 cm2/V. A coplanar-grid detector of size 10times10times5 mm3 has been fabricated from this material, and it shows an energy resolution of 2.1% FWHM at room
Proquest Dissertations and Theses Thesis Washington State University 2003 Publication Number Aai3110846 Isbn 9780496583805 Source Dissertation Abstracts International Volume 64 11 Section B Page 5713 113 P, 2003
Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have bee... more Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have been investigated using thermally stimulated spectroscopy with the general aim of identifying and then understanding the effects of the defects on the electrical and optical properties of these compounds. In order to identify and understand the effects of these defects (trapping levels), the samples were subjected to room temperature deformation, high temperature annealing, and dopants diffusion. The samples were always analyzed before and after any process. It is found that the trapping levels observed at ˜61 K and ˜114 K with thermal ionization energies of 0.12 +/- 0.01 eV and 0.23 +/- 0.01 eV and trapping cross-sections of 4.7 x 10-16 and 7.8 x 10-17 cm2 are associated with the isolated first and second ionized state of the cadmium vacancy, while trapping levels observed at ˜51 K and ˜94 K with thermal ionization energies of 0.09 +/- 0.01 eV and 0.18 +/- 0.01 eV and trapping cross-sections of 9.3 x 10 -17 and 6.8 x 10-17 cm2 are associated with first and second states of the isoelectronic oxygen-cadmium vacancy complex (VCd-OTe) respectively. In addition, we found that deep level trapping states located near the middle of the band gap (in the region between 230 K and 267 K) in undoped as grown CdTe are related to the tellurium antisite-cadmium vacancy complex (TeCd-V Cd) where the lowest thermal ionization state is 0.78 +/- 0.01 eV. The thermal ionization energies (transition energies) were extracted using variable heating rate and/or initial rise methods. Our results have been reinforced with theoretical calculations using linearized augmented plane wave (LAPW) within the local density approximation (LDA). Also, from our room temperature deformation, we have found evidence of three levels of dislocation defects in CdTe crystals. The first two energy levels, with ionization energies of E1 = 0.06 +/- 0.01 eV and E2 = 0.38 +/- 0.01 eV are due to Cd dislocations. The third deeper level, with ionization energy of E3 = 0.49 +/- 0.01 eV, is related to Te dislocations. In addition, we have found that the intensity of the induced dislocations, photoconductivity, and resistivity of the crystals are proportional to the deformation rate and the direction of the applied compression load. The annealing result showed that the applied load did not reach the yield point of the crystals; therefore, the induced deformation is elastic.
The excellent room temperature spectral performance of cadmium zinc telluride detectors grown via... more The excellent room temperature spectral performance of cadmium zinc telluride detectors grown via the Traveling Heater Method (THM) makes this approach suitable for the mass deployment of radiation detectors for applications in homeland security and medical imaging. This paper reports our progress in fabricating thicker and larger area detectors from THM grown CZT. We discuss the performance of such 20x20x10 mm 3, and 10x10x10 mm 3 monolithic pixellated detectors and virtual Frisch-Grid 4x4x12 mm3 devices, and describe the various physical properties of the materials.
High-performance semi-insulating single crystals of n-type Cd 0 9 Zn 0 1 Te (CZT) were grown usin... more High-performance semi-insulating single crystals of n-type Cd 0 9 Zn 0 1 Te (CZT) were grown using the traveling heater method (THM). X-ray and -ray detector configurations fabricated from this material have a room-temperature mean energy resolution of 4.3% FWHM for a 57 Co source (122 keV) and uniform pixel-to-pixel response on monolithic 20 20 5 mm 3 pixellated detectors. Energy resolution of 1% FWHM for 137 Cs (662 keV) has been measured on virtual Frisch-grid 4 4 11 mm 3 devices useful for homeland security applications. Additional characterization techniques including mobility-lifetime measurements, infrared microscopy, X-ray topography, and OPTICAL Deep Level Transient Spectroscopy (ODLTS) have demonstrated the superior quality of this THM CZT.
The spectral response of several crystals grown by the Traveling Heater Method (THM) were investi... more The spectral response of several crystals grown by the Traveling Heater Method (THM) were investigated. An energy resolution of 0.98% for a Pseudo Frisch-Grid of 4 4 9 mm 3 and 2.1% FWHM for a coplanar-grid of size 11 11 5 mm 3 were measured using 137 Cs-662 keV. In addition a 4% FWHM at 122 keV has also been measured on 20 20 5 mm 3 monolithic pixellated devices. The material shows great potential toward producing large-volume detectors with spectral performance that meets the requirement for high-resolution gamma-ray spectroscopy.
New results on the effects of small-scale defects on the charge-carrier transport in singlecrysta... more New results on the effects of small-scale defects on the charge-carrier transport in singlecrystal CdZnTe (CZT) material were produced. We conducted detailed studies of the role of Te inclusions in CZT by employing a highty collimated synchrotron x-ray radiation source available at Brookhaven's National Synchrotron Light Source (NSLS). We were able to induce polarization effects by irradiating specific areas with the detector. These measurements allowed the first quantitative comparison between areas that are free of Te inclusions and those with a relatively high concentration of inclusions. The results of these polarbtion studies will be reported.
High-quality large single crystals of Cd0.9Zn0.1Te (> 7 inch3) have been consistently produced by... more High-quality large single crystals of Cd0.9Zn0.1Te (> 7 inch3) have been consistently produced by the THM (solution growth) method. Various large-volume X-ray and gamma-ray detector configurations fabricated from this THM CZT material have produced detectors with excellent performance. A room-temperature mean energy resolution of 4.3% for a Co-57 source (122 keV) and uniform pixel-to-pixel response have been demonstrated on monolithic 20times20times5 mm3 pixellated detectors useful for imaging applications. In addition, energy resolution of <1% FWHM @ Cs-137 (662 keV) has been measured on virtual Frisch-Grid 4times4times11 mm3 devices useful for homeland security applications. Additional characterization techniques such as mu-tau measurements, infrared microscopy, X-ray topography and ODLTS have demonstrated the superior quality of this THM CZT. The results of material characterization measurements and detector tests will be presented.
Long term reliability is critical for a detector module to be used in applications that can not a... more Long term reliability is critical for a detector module to be used in applications that can not afford failure and require high accuracy such as medical imaging and homeland security. In this study, we report the reliability of pixellated Cadmium Zinc Telluride (CZT) detector modules fabricated from crystals grown by the Traveling Heater Method (THM). The reliability of the module which consists of the pixellated detector assembled to a PCB carrier board via conductive epoxy was studied with both a Quantitative Accelerated Life Test (QALT) as well as the Highly Accelerated Stress Test (HAST) which is a common form of a Qualitative Accelerated Life test. The robustness of the THM pixellated CZT detector modules is demonstrated via the pre- and post- accelerated life test comparison of the leakage current and the spectral performance of the assembled module. A shear test was also used to ensure the adhesion strength of the epoxy bonded method. To our knowledge, this type of study on pixellated CZT detector module has been very rare if not the first of its kind.
This work focuses on the thickness scalability of traveling heater method (THM) grown CdZnTe crys... more This work focuses on the thickness scalability of traveling heater method (THM) grown CdZnTe crystals to produce large volume detectors with optimized spectroscopic performance. To meet this challenge, we have tuned both our THM growth process, to grow 75 mm diameter ingots, and our postgrowth annealing process. We have increased the thickness of our sliced wafers from 6 to 12 and 18 mm allowing the production of 10 and 15 mm thick detectors. As the detectors' thickness is scaled up, the energy resolution of both types, as pseudo-Frisch grid and pixelated monolithic detectors showed no degradation indicating improved materials uniformity and transport properties.
Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have bee... more Intrinsic defects and impurities in undoped CdTe and Cd1-x ZnxTe semiconductor compounds have been investigated using thermally stimulated spectroscopy with the general aim of identifying and then understanding the effects of the defects on the electrical and optical properties of these compounds. In order to identify and understand the effects of these defects (trapping levels), the samples were subjected to room temperature deformation, high temperature annealing, and dopants diffusion. The samples were always analyzed before and after any process. It is found that the trapping levels observed at ˜61 K and ˜114 K with thermal ionization energies of 0.12 +/- 0.01 eV and 0.23 +/- 0.01 eV and trapping cross-sections of 4.7 x 10-16 and 7.8 x 10-17 cm2 are associated with the isolated first and second ionized state of the cadmium vacancy, while trapping levels observed at ˜51 K and ˜94 K with thermal ionization energies of 0.09 +/- 0.01 eV and 0.18 +/- 0.01 eV and trapping cross-sections of 9.3 x 10 -17 and 6.8 x 10-17 cm2 are associated with first and second states of the isoelectronic oxygen-cadmium vacancy complex (VCd-OTe) respectively. In addition, we found that deep level trapping states located near the middle of the band gap (in the region between 230 K and 267 K) in undoped as grown CdTe are related to the tellurium antisite-cadmium vacancy complex (TeCd-V Cd) where the lowest thermal ionization state is 0.78 +/- 0.01 eV. The thermal ionization energies (transition energies) were extracted using variable heating rate and/or initial rise methods. Our results have been reinforced with theoretical calculations using linearized augmented plane wave (LAPW) within the local density approximation (LDA). Also, from our room temperature deformation, we have found evidence of three levels of dislocation defects in CdTe crystals. The first two energy levels, with ionization energies of E1 = 0.06 +/- 0.01 eV and E2 = 0.38 +/- 0.01 eV are due to Cd dislocations. The third deeper level, with ionization energy of E3 = 0.49 +/- 0.01 eV, is related to Te dislocations. In addition, we have found that the intensity of the induced dislocations, photoconductivity, and resistivity of the crystals are proportional to the deformation rate and the direction of the applied compression load. The annealing result showed that the applied load did not reach the yield point of the crystals; therefore, the induced deformation is elastic.
... 7±4)10−17 cm2, respectively. In this paper we study the behavior of the isoelectronic oxygen-... more ... 7±4)10−17 cm2, respectively. In this paper we study the behavior of the isoelectronic oxygen-cation vacancy pair (OTe–VCd/Zn) in CdZnTe using TEES and first-principles total-energy calculations. We find that adding Zn to ...
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