About
Experience & Education
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University of Calgary
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Volunteer Experience
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Member of Judging Committee, Summer Undergraduate Research in Engineering (SURE)
McGill University
- Present 13 years 9 months
Science and Technology
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Member of Session Leaders, Summer Undergraduate Research in Engineering (SURE)
McGill University
- Present 13 years 9 months
Science and Technology
Publications
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Visible light-driven efficient overall water splitting using p-type metal-nitride nanowire arrays
Nature Communications
See publicationSolar water splitting for hydrogen generation can be a potential source of renewable energy for the future. Here we show that efficient and stable stoichiometric dissociation of water into hydrogen and oxygen can be achieved under visible light by eradicating the potential barrier on nonpolar surfaces of indium gallium nitride nanowires through controlled p-type dopant incorporation. An apparent quantum efficiency of ~12.3% is achieved for overall neutral (pH~7.0) water splitting under visible…
Solar water splitting for hydrogen generation can be a potential source of renewable energy for the future. Here we show that efficient and stable stoichiometric dissociation of water into hydrogen and oxygen can be achieved under visible light by eradicating the potential barrier on nonpolar surfaces of indium gallium nitride nanowires through controlled p-type dopant incorporation. An apparent quantum efficiency of ~12.3% is achieved for overall neutral (pH~7.0) water splitting under visible light illumination (400–475 nm). Moreover, using a double-band p-type gallium nitride/indium gallium nitride nanowire heterostructure, we show a solar-to-hydrogen conversion efficiency of ~1.8% under concentrated sunlight. The dominant effect of near-surface band structure in transforming the photocatalytic performance is elucidated. The stability and efficiency of this recyclable, wafer-level nanoscale metal-nitride photocatalyst in neutral water demonstrates their potential use for large-scale solar-fuel conversion.
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Defect-engineered GaN: Mg nanowire arrays for overall water splitting under violet light
Applied Physics Letter
See publicationWe report that by engineering the intra-gap defect related energy states in GaN nanowire arrays using Mg dopants, efficient and stable overall neutral water splitting can be achieved under violet light. Overall neutral water splitting on Rh/Cr2O3 co-catalyst decorated Mg doped GaN nanowires is demonstrated with intra-gap excitation up to 450 nm. Through optimized Mg doping, the absorbed photon conversion efficiency of GaN nanowires reaches ∼43% at 375–450 nm, providing a viable approach to…
We report that by engineering the intra-gap defect related energy states in GaN nanowire arrays using Mg dopants, efficient and stable overall neutral water splitting can be achieved under violet light. Overall neutral water splitting on Rh/Cr2O3 co-catalyst decorated Mg doped GaN nanowires is demonstrated with intra-gap excitation up to 450 nm. Through optimized Mg doping, the absorbed photon conversion efficiency of GaN nanowires reaches ∼43% at 375–450 nm, providing a viable approach to extend the solar absorption of oxide and non-oxide photocatalysts.
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Breaking the Carrier Injection Bottleneck of Phosphor-Free Nanowire White Light-Emitting Diodes
Nano Letter, American Chemical Society
See publicationWe have examined the carrier injection process of axial nanowire light-emitting diode (LED) structures and identified that poor carrier injection efficiency, due to the large surface recombination, is the primary cause for the extremely low output power of phosphor-free nanowire white LEDs. We have further developed InGaN/GaN/AlGaN dot-in-a-wire core–shell white LEDs on Si substrate, which can break the carrier injection efficiency bottleneck, leading to a massive enhancement in the output…
We have examined the carrier injection process of axial nanowire light-emitting diode (LED) structures and identified that poor carrier injection efficiency, due to the large surface recombination, is the primary cause for the extremely low output power of phosphor-free nanowire white LEDs. We have further developed InGaN/GaN/AlGaN dot-in-a-wire core–shell white LEDs on Si substrate, which can break the carrier injection efficiency bottleneck, leading to a massive enhancement in the output power. At room temperature, the devices can exhibit an output power of ∼1.5 mW, which is more than 2 orders of magnitude stronger than nanowire LEDs without shell coverage. Additionally, such phosphor-free nanowire white LEDs can deliver an unprecedentedly high color rendering index of ∼92–98 in both the warm and cool white regions, with the color rendering capability approaching that of an ideal light source, i.e. a blackbody.
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p-Type InN Nanowires
Nano Letter, American Chemical Society
See publicationIn this Letter, we demonstrate that with the merit of nanowire structure and a self-catalytic growth process p-type InN can be realized for the first time by “direct” magnesium (Mg) doping. The presence of Mg acceptor energy levels in InN is confirmed by photoluminescence experiments, and a direct evidence of p-type conduction is demonstrated unambiguously by studying the transfer characteristics of InN nanowire field effect transistors. Moreover, the near-surface Fermi-level of InN can be…
In this Letter, we demonstrate that with the merit of nanowire structure and a self-catalytic growth process p-type InN can be realized for the first time by “direct” magnesium (Mg) doping. The presence of Mg acceptor energy levels in InN is confirmed by photoluminescence experiments, and a direct evidence of p-type conduction is demonstrated unambiguously by studying the transfer characteristics of InN nanowire field effect transistors. Moreover, the near-surface Fermi-level of InN can be tuned from nearly intrinsic to p-type degenerate by controlling Mg dopant incorporation, which is in contrast to the commonly observed electron accumulation on the grown surfaces of Mg-doped InN films. First-principle calculation using the VASP electronic package further shows that the p-type surface formed on Mg-doped InN nanowires is highly stable energetically.
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One-Step Overall Water Splitting under Visible Light Using Multiband InGaN/GaN Nanowire Heterostructures
ACS, Nano, American Chemical Society
See publicationThe conversion of solar energy into hydrogen via water splitting process is one of the key sustainable technologies for future clean, storable, and renewable source of energy. Therefore, development of visible light-responsive and efficient photocatalyst material has been of immense interest, but with limited success. Here, we show that overall water splitting under visible-light irradiation can be achieved using a single photocatalyst material. Multiband InGaN/GaN nanowire heterostructures…
The conversion of solar energy into hydrogen via water splitting process is one of the key sustainable technologies for future clean, storable, and renewable source of energy. Therefore, development of visible light-responsive and efficient photocatalyst material has been of immense interest, but with limited success. Here, we show that overall water splitting under visible-light irradiation can be achieved using a single photocatalyst material. Multiband InGaN/GaN nanowire heterostructures, decorated with rhodium (Rh)/chromium-oxide (Cr2O3) core–shell nanoparticles can lead to stable hydrogen production from pure (pH 7.0) water splitting under ultraviolet, blue and green-light irradiation (up to 560 nm), the longest wavelength ever reported. At 440–450 nm wavelengths, the internal quantum efficiency is estimated to be 13%, the highest value reported in the visible spectrum. The turnover number under visible light well exceeds 73 in 12 h. Detailed analysis further confirms the stable photocatalytic activity of the nanowire heterostructures. This work establishes the use of metal-nitrides as viable photocatalyst for solar-powered artificial photosynthesis for the production of hydrogen and other solar fuels.
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Remarkably enhanced photocatalytic activity of laser ablated Au nanoparticle decorated BiFeO 3 nanowires under visible-light
Chemical Communications, Royal Society of Chemistry
See publicationHybrid photocatalysts consisting of single crystalline BiFeO3 nanowires and laser ablated Au nanoparticles were synthesized by a functionalization-step-free solution process. The 1.0 wt% Au nanoparticle decorated BiFeO3 nanowires exhibit [similar]30 times higher photocatalytic activity for water oxidation than that exhibited by the parent wires during the first 4 h.
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High efficiency photoelectrochemical water splitting and hydrogen generation using GaN nanowire photoelectrode
Nanotechnology, IOP Publishing
See publicationWe have studied the photoelectrochemical properties of both undoped and Si-doped GaN nanowire arrays in 1 mol l−1 solutions of hydrogen bromide and potassium bromide, which were used separately as electrolytes. It is observed that variations of the photocurrent with bias voltage depend strongly on the n-type doping in GaN nanowires in both electrolytes, which are analyzed in the context of GaN surface band bending and its variation with the incorporation of Si-doping. Maximum…
We have studied the photoelectrochemical properties of both undoped and Si-doped GaN nanowire arrays in 1 mol l−1 solutions of hydrogen bromide and potassium bromide, which were used separately as electrolytes. It is observed that variations of the photocurrent with bias voltage depend strongly on the n-type doping in GaN nanowires in both electrolytes, which are analyzed in the context of GaN surface band bending and its variation with the incorporation of Si-doping. Maximum incident-photon-to-current-conversion efficiencies of ~15% and 18% are measured for undoped and Si-doped GaN nanowires under ~350 nm light illumination, respectively. Stable hydrogen generation is also observed at a zero bias potential versus the counter-electrode.
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Understanding the role of Si doping on surface charge and optical properties: Photoluminescence study of intrinsic and Si-doped InN nanowires
American Physical Society
See publicationIn the present work, the photoluminescence (PL) characteristics of intrinsic and Si-doped InN nanowires are studied in detail. For intrinsic InN nanowires, the emission is due to band-to-band carrier recombination with the peak energy at ∼0.64 eV (at 300 K) and may involve free-exciton emission at low temperatures. The PL spectra exhibit a strong dependence on optical excitation power and temperature, which can be well characterized by the presence of very low residual electron density and the…
In the present work, the photoluminescence (PL) characteristics of intrinsic and Si-doped InN nanowires are studied in detail. For intrinsic InN nanowires, the emission is due to band-to-band carrier recombination with the peak energy at ∼0.64 eV (at 300 K) and may involve free-exciton emission at low temperatures. The PL spectra exhibit a strong dependence on optical excitation power and temperature, which can be well characterized by the presence of very low residual electron density and the absence or a negligible level of surface electron accumulation. In comparison, the emission of Si-doped InN nanowires is characterized by the presence of two distinct peaks located at ∼0.65 and ∼0.73–0.75 eV (at 300 K). Detailed studies further suggest that these low-energy and high-energy peaks can be ascribed to band-to-band carrier recombination in the relatively low-doped nanowire bulk region and Mahan exciton emission in the high-doped nanowire near-surface region, respectively; this is a natural consequence of dopant surface segregation. The resulting surface electron accumulation and Fermi-level pinning, due to the enhanced surface doping, are confirmed by angle-resolved x-ray photoelectron spectroscopy measurements on Si-doped InN nanowires, which is in direct contrast to the absence or a negligible level of surface electron accumulation in intrinsic InN nanowires. This work elucidates the role of charge-carrier concentration and distribution on the optical properties of InN nanowires.
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Tuning the surface charge properties of epitaxial InN nanowires
Nano Letter, American Chemical Society
See publicationWe have investigated the correlated surface electronic and optical properties of [0001]-oriented epitaxial InN nanowires grown directly on silicon. By dramatically improving the epitaxial growth process, we have achieved, for the first time, intrinsic InN both within the bulk and at nonpolar InN surfaces. The near-surface Fermi-level was measured to be 0.55 eV above the valence band maximum for undoped InN nanowires, suggesting the absence of surface electron accumulation and Fermi-level…
We have investigated the correlated surface electronic and optical properties of [0001]-oriented epitaxial InN nanowires grown directly on silicon. By dramatically improving the epitaxial growth process, we have achieved, for the first time, intrinsic InN both within the bulk and at nonpolar InN surfaces. The near-surface Fermi-level was measured to be 0.55 eV above the valence band maximum for undoped InN nanowires, suggesting the absence of surface electron accumulation and Fermi-level pinning. This result is in direct contrast to the problematic degenerate two-dimensional electron gas universally observed on grown surfaces of n-type degenerate InN. We have further demonstrated that the surface charge properties of InN nanowires, including the formation of two-dimensional electron gas and the optical emission characteristics can be precisely tuned through controlled n-type doping. At relatively high doping levels in this study, the near-surface Fermi-level was found to be pinned at 0.95–1.3 eV above the valence band maximum. Through these trends, well captured by the effective mass and ab initio materials modeling, we have unambiguously identified the definitive role of surface doping in tuning the surface charge properties of InN.
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Wafer-level photocatalytic water splitting on GaN nanowire arrays grown by molecular beam epitaxy
Nano Letter, American Chemical Society
See publicationWe report on the achievement of wafer-level photocatalytic overall water splitting on GaN nanowires grown by molecular beam epitaxy with the incorporation of Rh/Cr2O3 core–shell nanostructures acting as cocatalysts, through which H2 evolution is promoted by the noble metal core (Rh) while the water forming back reaction over Rh is effectively prevented by the Cr2O3 shell O2 diffusion barrier. The decomposition of pure water into H2 and O2 by GaN nanowires is confirmed to be a highly stable…
We report on the achievement of wafer-level photocatalytic overall water splitting on GaN nanowires grown by molecular beam epitaxy with the incorporation of Rh/Cr2O3 core–shell nanostructures acting as cocatalysts, through which H2 evolution is promoted by the noble metal core (Rh) while the water forming back reaction over Rh is effectively prevented by the Cr2O3 shell O2 diffusion barrier. The decomposition of pure water into H2 and O2 by GaN nanowires is confirmed to be a highly stable photocatalytic process, with the turnover number per unit time well exceeding the value of any previously reported GaN powder samples.
Honors & Awards
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Postdoctoral research scholarships-B3
Fonds de recherche du Québec Nature et technologies (FRQNT), Quebec, Canada
Secured 2nd position in Group-Energy for the session 2015-2017
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SPIE Optics and Photonics Education Scholarship
SPIE
For the potential long-range contributions to the field of optics, photonics, or related field
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Best Student oral presentation at the 30th North American Molecular Beam Epitaxy Conference
North American Molecular Beam Epitaxy
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Academic Gold Medal
Khulna University of Engineering and Technology
In recognition of outstanding performance in BSc. Highest GPA (3.85/4.00) in the class of 2001.
Languages
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English
Full professional proficiency
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Bangla
Full professional proficiency
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Hindi
Limited working proficiency
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Urdu
Elementary proficiency
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French
Elementary proficiency
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