Helen Jackson
Dr. Helen Jackson is currently a Machine Learning Engineer. She previously was a Machine Learning/AI consultant for DTRA, and Research Physicist/Data Scientist for Battelle. She was a Research Physicist for the Air Force Research Laboratory for 6 years and part time faculty at Wright State University. Her PhD is in Nuclear Physics, which she acquired at the Air Force Institute of Technology, specializing in radiation effects on semiconductors. Her research at the Air Force benefited military Air Defense. Her experimental, modeling and simulation efforts of radiation damaged semiconductors was used to obtain reliability and lifetime information, leading to more optimal device design and performance. She patented a method to achieve radiation hardness for Air Force sensors.
Previously as a Vanderbilt University Research Associate she did medical physics and developed a prototype for radiation dosimetry for selected skin cancers. She also did modelling used in nuclear nonproliferation with the Department of Energy and while at Fisk University.
In addition to her varied skills as a physicist, Dr. Jackson is an experienced and accomplished software engineer and machine learning scientist in Python, C++, and Java. Philanthropically, she is very active in mentoring the underrepresented in STEM and is a field staff member at many humanitarian and civic organizations.
Phone: 6158285080
Address: Washington,D.C.
Previously as a Vanderbilt University Research Associate she did medical physics and developed a prototype for radiation dosimetry for selected skin cancers. She also did modelling used in nuclear nonproliferation with the Department of Energy and while at Fisk University.
In addition to her varied skills as a physicist, Dr. Jackson is an experienced and accomplished software engineer and machine learning scientist in Python, C++, and Java. Philanthropically, she is very active in mentoring the underrepresented in STEM and is a field staff member at many humanitarian and civic organizations.
Phone: 6158285080
Address: Washington,D.C.
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Papers by Helen Jackson
with typical dimensions of 5x5~12m m3 are easy to produce and can be arranged into large arrays used for imaging and gamma-ray spectroscopy. In this paper, we report on further advances of the virtual Frischgrid detector design for the parallelepiped-shaped CZT crystals. Both the experimental testing and modeling results are described.
Keywords: CdZnTe, gamma ray detectors, Frisch-grid
CdZnTe (CZT) material can degrade the performance of CZT
detectors. These microscopic defects trap the free electrons generated
by incident radiation, so entailing significant fluctuations
in the total collected charge and thereby strongly affecting the
energy resolution of thick (long-drift) detectors. Such effects
were demonstrated in thin planar detectors, and, in many cases,
they proved to be the dominant cause of the low performance
of thick detectors, wherein the fluctuations in the charge losses
accumulate along the charge’s drift path. We continued studying
this effect using different tools and techniques. We employed a
dedicated beam-line recently established at BNL’s National Synchrotron
Light Source for characterizing semiconductor radiation
detectors, along with an IR transmission microscope system, the
combination of which allowed us to correlate the concentration
of defects with the devices’ performances. We present here our
new results from testing over 50 CZT samples grown by different
techniques. Our goals are to establish tolerable limits on the size
and concentrations of these detrimental Te inclusions in CZT
material, and to provide feedback to crystal growers to reduce
their numbers in the material.
AlGaN\GaN heterojunction devices can not only improve device performance but also radiation
harden the device while preserving the reliability and performance. In this study, the effects of
passivation layer thickness were investigated by using various thicknesses (0, 20, 50 and 120
nanometers) on bare epilayer AlGaN\GaN structures which were then measured before and
immediately after 1.0 MeV electron irradiation at fluences from 5 x 1015 cm-2 to 1016 cm-2. The
irradiation was applied in order to increase the electron trapping at the interface, thus providing
an enhanced interface quality. It has been shown previously that this irradiation produces point
defects and creates acceptors [1,2]. Hall measurements were used pre- and post-irradiation to
observe changes in carrier concentration and mobility as a function of fluence, energy, and total
dose. Hall carrier density data indicates the surface states are donors. Most importantly, these
measurements indicate preservation of mobility and conductivity within the optimal range of
Si3N4 thickness. This optimal range was found to be 50 to 120 nm.
Drafts by Helen Jackson
H. Jackson, Department of Physics, Wright State University, Dayton, Ohio 45431 USA
Abstract
Radiation changes the channel carrier density and increases the scattering in High Electron Mobility Transistors (HEMT’s). The channel in SiNx/AlGaN/GaN is described as a two-dimensional electron gas (2DEG) and is where the carriers exist. Structural parameters affect the 2DEG, and hence all other device metrics. An AlN inter-layer reduces the alloy scattering by acting as a barrier between the 2DEG wave function and the AlGaN. This can be shown in 2DEG wave function models. The AlN inter-layer adds to polarization, which then raises energy bands up relative to the Fermi level.
The interface roughness scattering potential amplitude V0 in the quantum well is approximately determined by assuming that local fluctuations of the interface position and of the roughness amplitude shrinks with well width. As the 2DEG waveform moves closer to the barrier (due possibly to things like increases in carrier density), there is scattering from interface roughness. Structures wherein the higher waveform sub-bands fill quicker, like those with a GaN cap, will have less interface roughness scattering and thus higher mobility because the higher sub-bands are further removed from the AlGaN interface.
Talks by Helen Jackson
with typical dimensions of 5x5~12m m3 are easy to produce and can be arranged into large arrays used for imaging and gamma-ray spectroscopy. In this paper, we report on further advances of the virtual Frischgrid detector design for the parallelepiped-shaped CZT crystals. Both the experimental testing and modeling results are described.
Keywords: CdZnTe, gamma ray detectors, Frisch-grid
CdZnTe (CZT) material can degrade the performance of CZT
detectors. These microscopic defects trap the free electrons generated
by incident radiation, so entailing significant fluctuations
in the total collected charge and thereby strongly affecting the
energy resolution of thick (long-drift) detectors. Such effects
were demonstrated in thin planar detectors, and, in many cases,
they proved to be the dominant cause of the low performance
of thick detectors, wherein the fluctuations in the charge losses
accumulate along the charge’s drift path. We continued studying
this effect using different tools and techniques. We employed a
dedicated beam-line recently established at BNL’s National Synchrotron
Light Source for characterizing semiconductor radiation
detectors, along with an IR transmission microscope system, the
combination of which allowed us to correlate the concentration
of defects with the devices’ performances. We present here our
new results from testing over 50 CZT samples grown by different
techniques. Our goals are to establish tolerable limits on the size
and concentrations of these detrimental Te inclusions in CZT
material, and to provide feedback to crystal growers to reduce
their numbers in the material.
AlGaN\GaN heterojunction devices can not only improve device performance but also radiation
harden the device while preserving the reliability and performance. In this study, the effects of
passivation layer thickness were investigated by using various thicknesses (0, 20, 50 and 120
nanometers) on bare epilayer AlGaN\GaN structures which were then measured before and
immediately after 1.0 MeV electron irradiation at fluences from 5 x 1015 cm-2 to 1016 cm-2. The
irradiation was applied in order to increase the electron trapping at the interface, thus providing
an enhanced interface quality. It has been shown previously that this irradiation produces point
defects and creates acceptors [1,2]. Hall measurements were used pre- and post-irradiation to
observe changes in carrier concentration and mobility as a function of fluence, energy, and total
dose. Hall carrier density data indicates the surface states are donors. Most importantly, these
measurements indicate preservation of mobility and conductivity within the optimal range of
Si3N4 thickness. This optimal range was found to be 50 to 120 nm.
H. Jackson, Department of Physics, Wright State University, Dayton, Ohio 45431 USA
Abstract
Radiation changes the channel carrier density and increases the scattering in High Electron Mobility Transistors (HEMT’s). The channel in SiNx/AlGaN/GaN is described as a two-dimensional electron gas (2DEG) and is where the carriers exist. Structural parameters affect the 2DEG, and hence all other device metrics. An AlN inter-layer reduces the alloy scattering by acting as a barrier between the 2DEG wave function and the AlGaN. This can be shown in 2DEG wave function models. The AlN inter-layer adds to polarization, which then raises energy bands up relative to the Fermi level.
The interface roughness scattering potential amplitude V0 in the quantum well is approximately determined by assuming that local fluctuations of the interface position and of the roughness amplitude shrinks with well width. As the 2DEG waveform moves closer to the barrier (due possibly to things like increases in carrier density), there is scattering from interface roughness. Structures wherein the higher waveform sub-bands fill quicker, like those with a GaN cap, will have less interface roughness scattering and thus higher mobility because the higher sub-bands are further removed from the AlGaN interface.