Ahmad E Islam | US Air Force Research Laboratory (original) (raw)

Papers by Ahmad E Islam

IEEE Transactions on Electron Devices, Feb 1, 2023

The engineering of defects in low-dimensional materials can enable the modulation of their optica... more The engineering of defects in low-dimensional materials can enable the modulation of their optical, electrical, thermal, and structural properties. We have previously shown the ability to engineer precision patterned defects in graphene by electron beam irradiation in a controlled water vapor ambient within an environmental scanning electron microscope (ESEM). However, the relationship between instrumental parameters and structural changes in graphene are unexplored. Here, we investigate the relationships between parameters such as pressure, electron dose, and acceleration voltage on the electronic and structural properties of graphene as probed by Raman spectroscopy. There are dependencies on all of the studied parameters but electron dose is the dominant parameter that shows the most intense levels of structural modulation. Interestingly, control of instrumental parameters allows for the precision tailoring of features such as resolution (as determined by the beamskirting effect),...

APL Materials, 2022

Gallium Oxide has undergone rapid technological maturation over the last decade, pushing it to th... more Gallium Oxide has undergone rapid technological maturation over the last decade, pushing it to the forefront of ultra-wide band gap semiconductor technologies. Maximizing the potential for a new semiconductor system requires a concerted effort by the community to address technical barriers which limit performance. Due to the favorable intrinsic material properties of gallium oxide, namely, critical field strength, widely tunable conductivity, mobility, and melt-based bulk growth, the major targeted application space is power electronics where high performance is expected at low cost. This Roadmap presents the current state-of-the-art and future challenges in 15 different topics identified by a large number of people active within the gallium oxide research community. Addressing these challenges will enhance the state-of-the-art device performance and allow us to design efficient, high-power, commercially scalable microelectronic systems using the newest semiconductor platform.

ECS Journal of Solid State Science and Technology, 2020

This work presents electrical characterization and analysis of the dominant charge transport mech... more This work presents electrical characterization and analysis of the dominant charge transport mechanism suggesting inhomogeneous, filamentary conduction for a lithium niobate switching layer based memristor for use in neuromorphic computing. Memristor conductivity has been investigated both for the high and low resistance states. It is suggested that when the device is in a high resistance state, deep trap energy level within the switching layer initiate the device conduction process. The elastic trap assisted tunneling mechanism with a simple steady state approach agrees with the experimental measurements in the high resistance state. This work considers existence of inhomogeneously distributed positively charged oxygen ions/vacancies (within the oxygen deficient switching layer) as the deep trap energy level, required for electron tunneling from memristor electrode. Alternatively, ohmic conduction was found to be the main mechanism for the memristor on state conductivity at room te...

Microscopy and Microanalysis, 2018

In order to monitor biological markers of human performance, such as neuropeptide Y (NPY), orexin... more In order to monitor biological markers of human performance, such as neuropeptide Y (NPY), orexin A, cortisol, interleukin-6 (IL-6), or troponin, biosensors must be able to selectively detect the target peptide with sub-10 pM sensitivity. The use of graphene-based field effect transistor (g-FET) sensors has been used to detect a variety of macromolecules such as RNA, DNA, peptides, and small toxic compounds [1]. The conductive graphene surface is functionalized with biological recognition elements (BREs) specific for the target peptide that consist of short amino acid sequences obtained via the phage display protocol [2]. To fully characterize the BRE, its local deformation and attachment to its target as well as the behavior of target peptide on the graphene surface during sensing (in operando bio-sensing) we use a combination of super-resolution microscopy, transmission electron microscopy (TEM), and liquid cell transmission electron microscopy (LC-TEM). Here we present the characterization of a Neuropeptide Y specific g-FET biosensor.

ECS Meeting Abstracts, 2011

not Available.

Microscopy and Microanalysis, 2017

Microscopy and Microanalysis, 2017

Microscopy and Microanalysis, 2017

IEEE Transactions on Device and Materials Reliability, 2016

In the history of electronics, solid state materials replaced the vacuum parts to reduce power co... more In the history of electronics, solid state materials replaced the vacuum parts to reduce power consumption and to obtain better reliability at a reduced cost. Size of solid state transistors continued to reduce since its introduction and currently we have transistors with dimensions in the order of ~ 10 nm. This down scaling of transistor dimension accompanied with proportionate changes in supply voltage so that the overall power consumption stays below a tolerable limit. The situation changed dramatically when requirements of proper electrostatic control over the entire length of the transistor and its reliable operation stopped supply voltage scaling, increased off-state leakage, and hence caused exponential increase in power consumption. The introduction of high-κ gate dielectric and then multiple/surround gate within the CMOS architecture have improved the situation, but still have not provided the complete solution for the future. For future electronic devices, we need switches with extremely low off-state leakage, small supply voltage, and high drive current without compromising the yield and reliability currently available in modern-day nanoscale transistors. The available options are based on extensions of current CMOS transistors by using nanowires, III-V compounds, carbon nanomaterials, transition metal dichalcogenides as channel, ferroelectrics as dielectric, and ferromagnets as source/drain. On the other hand, device architectures that are completely different from conventional CMOS (so called beyond CMOS devices) like tunnel transistors, nano-electro-mechanical devices, and impact ionization transistors are also under consideration for future electronics. The performance of many of these beyond CMOS devices is yet to be comparable to that obtained in the current-day CMOS transistors. In addition, many of these proposed devices have a number of classical and some novel reliability concerns. This review article presents reliability concerns for a set of extended and beyond CMOS devices and shows that defects in different parts of these devices require detailed study to ensure their usability in electronics industry. Therefore, in addition to the current ongoing research to obtain better performance using the proposed devices, a parallel reliability analysis is also needed. This kind of early stage reliability analysis may reveal whether any reliability concern is intrinsically related to the device design-hence suggest us to look for alternative device concepts for future CMOS.

Nano Letters, 2014

This report was cleared for public release by the USAF 88th Air Base Wing (88 ABW) Public Affairs... more This report was cleared for public release by the USAF 88th Air Base Wing (88 ABW) Public Affairs Office (PAO) and is available to the general public, including foreign nationals. Copies may be obtained from the Defense Technical Information Center (DTIC) (http://www.dtic.mil).

IMAPSource Proceedings

We studied the application of Beta-Ga2O3 for high temperature operation up to 500C. Field effect ... more We studied the application of Beta-Ga2O3 for high temperature operation up to 500C. Field effect transistors were fabricated using epitaxial films grown on insulating Beta-Ga2O3 substrates. Variable temperature DC measurements were performed in vacuum and air ambient. Measurements revealed a reduction in on/off ratio for the devices due to increase in thermionic emission over the gate/dielectric barrier of MOSFET and over the gate/semiconductor barrier of MESFET. Devices also exhibited detrapping of electrons from interface traps with the increase in temperature. After the devices were tested intermittently at different high temperatures in vacuum or in air ambient, suggesting no change in semiconductor and contact properties.

Advanced Materials Interfaces

2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID)

Inhalation of IPA impairs cognition and depresses the nervous system. Current gas-phase sensors a... more Inhalation of IPA impairs cognition and depresses the nervous system. Current gas-phase sensors are unable to selectively detect isopropyl alcohol from other volatile organic compounds. We present the development of bioinspired sensors using nanomaterials to provide real-time monitoring and differentiate IPA from background compounds.

IEEE Electron Device Letters

We demonstrate a passivated MESFET fabricated on (010) Si-doped β-Ga 2 O 3 with breakdown over 2.... more We demonstrate a passivated MESFET fabricated on (010) Si-doped β-Ga 2 O 3 with breakdown over 2.4 kV without field plates, high Power Figure of Merit (PFOM), and high estimated Huang's Material Figure of Merit (HMFOM), owing to low gate charge and high breakdown. MESFETs with 13 μm source-drain spacing and 75 nm channel exhibited a current density of 61 mA/mm, peak transconductance of 27 mS/mm, and on-resistance of 133 • mm. The device showed a PFOM competitive with state-of-theart β-Ga 2 O 3 devices and a record high estimated HMFOM for a β-Ga 2 O 3 device, competitive with commercial wide-band gap devices. This demonstrates high-performance β-Ga 2 O 3 devices as viable multi-kV high-voltage power switches. Index Terms-Field effect transistors, gallium oxide, MESFET, power transistors, ultra wide band gap semiconductors. I. INTRODUCTION β-Ga 2 O 3 is an emerging ultra-wide band gap (UWBG) semiconductor that shows great promise in the highvoltage, high-power, and high-efficiency device space, particularly for power switching and switch-mode amplification [1], [2]. β-Ga 2 O 3 has a range of compatible shallow n-type dopants, including Sn, Si, and Ge [3], allowing for tunable carrier densities from 10 15 cm −3 to >10 20 cm −3 [4], [5] enabling a wide range of breakdown voltages V bk with low on resistance R on. The material has a high critical electric field strength E c estimated at 8 MV/cm due to its wide band

NAECON 2021 - IEEE National Aerospace and Electronics Conference, 2021

As technology continues to move forward, the demand for smaller, more efficient radio frequency (... more As technology continues to move forward, the demand for smaller, more efficient radio frequency (RF) devices capable of operating at higher voltages, temperatures, and frequencies also increases. Devices made using the beta phase of gallium oxide (<tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf>) have the potential to operate at a high voltage and temperature. Combining the capacitance enhancement available in negative capacitance (NC) ferroelectric dielectrics with the benefits of <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf> shows promise for the development of the next-generation RF devices. In this paper, we work towards the integration of ferroelectric Hf<inf>0.8</inf>Zr<inf>0.2</inf>O<inf>2</inf> films on <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf> and fabricate different capacitive structures. We characterize these capacitors using capacitance-voltage and polarization-voltage measurements and study the impact of annealing temperature on the polarization of the Hf<inf>0.8</inf>Zr<inf>0.2</inf>O<inf>2</inf> films. Results show that saturation polarization, remnant polarization, and capacitance of the ferroelectric film increase with higher annealing temperatures. Considering that temperature could be a key factor in the fabrication and operation of RF devices made with <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf>, our study paves the way for the integration of these NC-ferroelectric materials on <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf>.

Applied Physics Letters, 2020

The path to achieving integrated RF and power conversion circuitry using the b-Ga 2 O 3 material ... more The path to achieving integrated RF and power conversion circuitry using the b-Ga 2 O 3 material system is described with regard to the materials high Johnson's RF figure of merit. Recent results, including large signal data at V D ¼ 50 V, are provided, showing progress in achieving highvoltage RF operation. Additionally, progress in achieving high-gain devices through gate length scaling is also benchmarked by a record RF power device with a gate length of 0.5 lm achieving a 2.1 GHz lm f T À L G product. These results are compared with state-of-the-art RF devices, and the expectations for b-Ga 2 O 3 at this point in its maturity throughout this Letter with future milestones laid out to measure progress. The conclusion includes near-and long-term projections for b-Ga 2 O 3 devices for RF based on the results and projected milestones presented.

Carbon, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

IEEE Transactions on Electron Devices, Feb 1, 2023

The engineering of defects in low-dimensional materials can enable the modulation of their optica... more The engineering of defects in low-dimensional materials can enable the modulation of their optical, electrical, thermal, and structural properties. We have previously shown the ability to engineer precision patterned defects in graphene by electron beam irradiation in a controlled water vapor ambient within an environmental scanning electron microscope (ESEM). However, the relationship between instrumental parameters and structural changes in graphene are unexplored. Here, we investigate the relationships between parameters such as pressure, electron dose, and acceleration voltage on the electronic and structural properties of graphene as probed by Raman spectroscopy. There are dependencies on all of the studied parameters but electron dose is the dominant parameter that shows the most intense levels of structural modulation. Interestingly, control of instrumental parameters allows for the precision tailoring of features such as resolution (as determined by the beamskirting effect),...

APL Materials, 2022

Gallium Oxide has undergone rapid technological maturation over the last decade, pushing it to th... more Gallium Oxide has undergone rapid technological maturation over the last decade, pushing it to the forefront of ultra-wide band gap semiconductor technologies. Maximizing the potential for a new semiconductor system requires a concerted effort by the community to address technical barriers which limit performance. Due to the favorable intrinsic material properties of gallium oxide, namely, critical field strength, widely tunable conductivity, mobility, and melt-based bulk growth, the major targeted application space is power electronics where high performance is expected at low cost. This Roadmap presents the current state-of-the-art and future challenges in 15 different topics identified by a large number of people active within the gallium oxide research community. Addressing these challenges will enhance the state-of-the-art device performance and allow us to design efficient, high-power, commercially scalable microelectronic systems using the newest semiconductor platform.

ECS Journal of Solid State Science and Technology, 2020

This work presents electrical characterization and analysis of the dominant charge transport mech... more This work presents electrical characterization and analysis of the dominant charge transport mechanism suggesting inhomogeneous, filamentary conduction for a lithium niobate switching layer based memristor for use in neuromorphic computing. Memristor conductivity has been investigated both for the high and low resistance states. It is suggested that when the device is in a high resistance state, deep trap energy level within the switching layer initiate the device conduction process. The elastic trap assisted tunneling mechanism with a simple steady state approach agrees with the experimental measurements in the high resistance state. This work considers existence of inhomogeneously distributed positively charged oxygen ions/vacancies (within the oxygen deficient switching layer) as the deep trap energy level, required for electron tunneling from memristor electrode. Alternatively, ohmic conduction was found to be the main mechanism for the memristor on state conductivity at room te...

Microscopy and Microanalysis, 2018

In order to monitor biological markers of human performance, such as neuropeptide Y (NPY), orexin... more In order to monitor biological markers of human performance, such as neuropeptide Y (NPY), orexin A, cortisol, interleukin-6 (IL-6), or troponin, biosensors must be able to selectively detect the target peptide with sub-10 pM sensitivity. The use of graphene-based field effect transistor (g-FET) sensors has been used to detect a variety of macromolecules such as RNA, DNA, peptides, and small toxic compounds [1]. The conductive graphene surface is functionalized with biological recognition elements (BREs) specific for the target peptide that consist of short amino acid sequences obtained via the phage display protocol [2]. To fully characterize the BRE, its local deformation and attachment to its target as well as the behavior of target peptide on the graphene surface during sensing (in operando bio-sensing) we use a combination of super-resolution microscopy, transmission electron microscopy (TEM), and liquid cell transmission electron microscopy (LC-TEM). Here we present the characterization of a Neuropeptide Y specific g-FET biosensor.

ECS Meeting Abstracts, 2011

not Available.

Microscopy and Microanalysis, 2017

Microscopy and Microanalysis, 2017

Microscopy and Microanalysis, 2017

IEEE Transactions on Device and Materials Reliability, 2016

In the history of electronics, solid state materials replaced the vacuum parts to reduce power co... more In the history of electronics, solid state materials replaced the vacuum parts to reduce power consumption and to obtain better reliability at a reduced cost. Size of solid state transistors continued to reduce since its introduction and currently we have transistors with dimensions in the order of ~ 10 nm. This down scaling of transistor dimension accompanied with proportionate changes in supply voltage so that the overall power consumption stays below a tolerable limit. The situation changed dramatically when requirements of proper electrostatic control over the entire length of the transistor and its reliable operation stopped supply voltage scaling, increased off-state leakage, and hence caused exponential increase in power consumption. The introduction of high-κ gate dielectric and then multiple/surround gate within the CMOS architecture have improved the situation, but still have not provided the complete solution for the future. For future electronic devices, we need switches with extremely low off-state leakage, small supply voltage, and high drive current without compromising the yield and reliability currently available in modern-day nanoscale transistors. The available options are based on extensions of current CMOS transistors by using nanowires, III-V compounds, carbon nanomaterials, transition metal dichalcogenides as channel, ferroelectrics as dielectric, and ferromagnets as source/drain. On the other hand, device architectures that are completely different from conventional CMOS (so called beyond CMOS devices) like tunnel transistors, nano-electro-mechanical devices, and impact ionization transistors are also under consideration for future electronics. The performance of many of these beyond CMOS devices is yet to be comparable to that obtained in the current-day CMOS transistors. In addition, many of these proposed devices have a number of classical and some novel reliability concerns. This review article presents reliability concerns for a set of extended and beyond CMOS devices and shows that defects in different parts of these devices require detailed study to ensure their usability in electronics industry. Therefore, in addition to the current ongoing research to obtain better performance using the proposed devices, a parallel reliability analysis is also needed. This kind of early stage reliability analysis may reveal whether any reliability concern is intrinsically related to the device design-hence suggest us to look for alternative device concepts for future CMOS.

Nano Letters, 2014

This report was cleared for public release by the USAF 88th Air Base Wing (88 ABW) Public Affairs... more This report was cleared for public release by the USAF 88th Air Base Wing (88 ABW) Public Affairs Office (PAO) and is available to the general public, including foreign nationals. Copies may be obtained from the Defense Technical Information Center (DTIC) (http://www.dtic.mil).

IMAPSource Proceedings

We studied the application of Beta-Ga2O3 for high temperature operation up to 500C. Field effect ... more We studied the application of Beta-Ga2O3 for high temperature operation up to 500C. Field effect transistors were fabricated using epitaxial films grown on insulating Beta-Ga2O3 substrates. Variable temperature DC measurements were performed in vacuum and air ambient. Measurements revealed a reduction in on/off ratio for the devices due to increase in thermionic emission over the gate/dielectric barrier of MOSFET and over the gate/semiconductor barrier of MESFET. Devices also exhibited detrapping of electrons from interface traps with the increase in temperature. After the devices were tested intermittently at different high temperatures in vacuum or in air ambient, suggesting no change in semiconductor and contact properties.

Advanced Materials Interfaces

2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID)

Inhalation of IPA impairs cognition and depresses the nervous system. Current gas-phase sensors a... more Inhalation of IPA impairs cognition and depresses the nervous system. Current gas-phase sensors are unable to selectively detect isopropyl alcohol from other volatile organic compounds. We present the development of bioinspired sensors using nanomaterials to provide real-time monitoring and differentiate IPA from background compounds.

IEEE Electron Device Letters

We demonstrate a passivated MESFET fabricated on (010) Si-doped β-Ga 2 O 3 with breakdown over 2.... more We demonstrate a passivated MESFET fabricated on (010) Si-doped β-Ga 2 O 3 with breakdown over 2.4 kV without field plates, high Power Figure of Merit (PFOM), and high estimated Huang's Material Figure of Merit (HMFOM), owing to low gate charge and high breakdown. MESFETs with 13 μm source-drain spacing and 75 nm channel exhibited a current density of 61 mA/mm, peak transconductance of 27 mS/mm, and on-resistance of 133 • mm. The device showed a PFOM competitive with state-of-theart β-Ga 2 O 3 devices and a record high estimated HMFOM for a β-Ga 2 O 3 device, competitive with commercial wide-band gap devices. This demonstrates high-performance β-Ga 2 O 3 devices as viable multi-kV high-voltage power switches. Index Terms-Field effect transistors, gallium oxide, MESFET, power transistors, ultra wide band gap semiconductors. I. INTRODUCTION β-Ga 2 O 3 is an emerging ultra-wide band gap (UWBG) semiconductor that shows great promise in the highvoltage, high-power, and high-efficiency device space, particularly for power switching and switch-mode amplification [1], [2]. β-Ga 2 O 3 has a range of compatible shallow n-type dopants, including Sn, Si, and Ge [3], allowing for tunable carrier densities from 10 15 cm −3 to >10 20 cm −3 [4], [5] enabling a wide range of breakdown voltages V bk with low on resistance R on. The material has a high critical electric field strength E c estimated at 8 MV/cm due to its wide band

NAECON 2021 - IEEE National Aerospace and Electronics Conference, 2021

As technology continues to move forward, the demand for smaller, more efficient radio frequency (... more As technology continues to move forward, the demand for smaller, more efficient radio frequency (RF) devices capable of operating at higher voltages, temperatures, and frequencies also increases. Devices made using the beta phase of gallium oxide (<tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf>) have the potential to operate at a high voltage and temperature. Combining the capacitance enhancement available in negative capacitance (NC) ferroelectric dielectrics with the benefits of <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf> shows promise for the development of the next-generation RF devices. In this paper, we work towards the integration of ferroelectric Hf<inf>0.8</inf>Zr<inf>0.2</inf>O<inf>2</inf> films on <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf> and fabricate different capacitive structures. We characterize these capacitors using capacitance-voltage and polarization-voltage measurements and study the impact of annealing temperature on the polarization of the Hf<inf>0.8</inf>Zr<inf>0.2</inf>O<inf>2</inf> films. Results show that saturation polarization, remnant polarization, and capacitance of the ferroelectric film increase with higher annealing temperatures. Considering that temperature could be a key factor in the fabrication and operation of RF devices made with <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf>, our study paves the way for the integration of these NC-ferroelectric materials on <tex>$\beta$</tex>-Ga<inf>2</inf>O<inf>3</inf>.

Applied Physics Letters, 2020

The path to achieving integrated RF and power conversion circuitry using the b-Ga 2 O 3 material ... more The path to achieving integrated RF and power conversion circuitry using the b-Ga 2 O 3 material system is described with regard to the materials high Johnson's RF figure of merit. Recent results, including large signal data at V D ¼ 50 V, are provided, showing progress in achieving highvoltage RF operation. Additionally, progress in achieving high-gain devices through gate length scaling is also benchmarked by a record RF power device with a gate length of 0.5 lm achieving a 2.1 GHz lm f T À L G product. These results are compared with state-of-the-art RF devices, and the expectations for b-Ga 2 O 3 at this point in its maturity throughout this Letter with future milestones laid out to measure progress. The conclusion includes near-and long-term projections for b-Ga 2 O 3 devices for RF based on the results and projected milestones presented.

Carbon, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.