Overview

Dr. Hubbard’s research focuses on Photovoltaic and Optoelectronic Devices, III-V Semiconductors, and Vapor Phase Epitaxy. Through grants from the National Science Foundation and New York State, Dr. Hubbard has been able to secure funding to build a Metal Organic Chemical Vapor Deposition (MOCVD) system in the Semiconductor Material & Fabrication Laboratory (SMFL) on the RIT campus. This is the only system of its kind in New York State.  Another toolset, purchased through support of the Office of Naval Research allows RIT the capacity to measure both in-situ and ex-situ the strain, bandgap and material quality of novel materials grown using our newly acquired MOCVD tool. The toolset is devoted to the development of III-V nanostructured devices and materials for power generation, energy harvesting and adaptive multimodal sensing.

Interests

  • Epitaxial Crystal Growth by Metalorganic Chemical Vapor Deposition
  • Semiconductor Device Design and Fabrication
  • MOCVD System Design
  • Nano-structures (quantum wires/dots) for enhanced efficiency photovoltaic cells.
  • High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrator Application
  • Growth of semiconductor nanostructures using MOVPE growth techniques
  • Novel Approaches to Power Conversion (alphavoltaics, thin-film III-Vs)
  • Nanostructured gas/chemical sensors

Current Research Projects

  • Metal Organic Chemical Vapor Deposition (MOCVD) Facility

    Metal Organic Chemical Vapor Deposition (MOCVD) Facility

    This $1.75M capital equipment project is for the design and implementation of III-V material growth system using Metal Organic Chemical Vapor Deposition (MOCVD).

    Metal Organic Chemical Vapor Deposition (MOCVD) Facility

    This $1.75M capital equipment project is for the design and implementation of III-V material growth system using Metal Organic Chemical Vapor Deposition (MOCVD). The equipment, facility upgrades and personnel support for this project is funded in part by the National Science Foundation (NSF), Empire State Development (NYS), the Department of Defense, NASA and the Rochester Institute of Technology (RIT), VP of Research (https://www.rit.edu/research/about-us/vice-president-research ) and the RIT-Kate Gleason College of Engineering (https://www.rit.edu/kgcoe/ ). The system is being installed in the Semiconductor and Mircrosystems Fabrication Laboratory (http://www.smfl.rit.edu/  (SMFL), with an expected completion date of September 2015.

    The system will be devoted to the growth of III-V nanostructured materials and devices. The MOCVD has been proven to provide the variety of materials, thickness, composition, and doping control necessary for the various nanomaterials and nanostructures. Current programs that utilize the MOCVD include the development of InAs quantum dots for high efficiency solar cells, III-V materials integrated with silicon based nanophotonics, next generation imaging array detectors and nanostructured 111-V devices for radioisotope micro-batteries for health and security related microsystems. Adding on-site III-V growth capability will complement RIT’s outstanding processing and characterization facilities and will provide our students with state-of-the-art tools to excel in their chosen fields of study. (NSF)

     

    The materials grown by MOCVD have led to spectacular technological advancements in the last 25 years, including the lasers and photo-detectors that power the backbone of the internet and other long distance communication systems, transistors used to send and receive signals in our mobile communication devices, high luminous efficiency white lightening, high storage density, optical disks and some of the highest efficiency solar cells ever created. The MOCVD system will be part of RIT’s state-of-the-art clean room user facility and will provide essential resources and new capabilities in multiple nanotechnology applications for our regional academic and industrial partners. Only 1 other university in the US has the type of MOCVD capability, thus putting RIT in an elite category for research and development of new materials. (NYS)

     

    Applications for MOCVD use include high-efficiency nanostructured photovoltaics, radioisotope power generation, III-V on Si photovoltaics and Optoelectronics, and long wavelength infrared detectors. These applications require additional monitoring equipment. The LayTec EpiCurveTT measures materials reflectivity, composition and stain in-situ during MOCVD growth and a Nanometrics RPM Blue photoluminescence mapping tool and Electrochemical Capacitance Voltage Profiler to correlate ex-situ the materials bandgap, alloy composition, doping and defect profiles. This combined toolset, when used with the new RIT MOCVD facility, will give unprecedented characterization capability to rapidly develop the new materials and devices that are of interest to sponsor agencies. This equipment will provide for unmatched uniformity, control and materials utilization efficiency. (DoD)

     

    Photovoltaics is at the forefront of a large push in the energy sector towards increasing efficiency. In the space community, the benefits from high efficiency photovoltaic technologies include increased mass specific power, reduced payload volume and potential for higher radiation missions. In order to realize these objectives, the efficiency of photovoltaic devices must increase through improving the current state-of-the-art technologies or by investigating novel approaches. Various epitaxial growth techniques have been investigated to increase the power generated from photovoltaics, while many of these techniques make use of nanostructures that enable quantum confinement and bandgap engineering. With the use of nanostructures that enable quantum confinement, it is possible to absorb efficiently at multiple energy levels. Various techniques are currently being pursued to achieve high efficiency quantum confined solar cells, of which the nipi doping superlattice solar cells, quantum dot bandgap engineered or intermediate band solar cells are a few. The objective of this research is to pursue to use of quantom dots within a doping superlattice to potentially realize an intermediate band solar cell. (NASA)

  • Highly Mismatched GaSb-GaAs thin film Multijunction Solar Cells

    Highly Mismatched GaSb-GaAs thin film Multijunction Solar Cells

    This purpose of this grant is to increase the efficiency of solar cells using highly mismatched, multi-junction (MJ) Sb-based solar cell with low defect density and optimal bandgap subcells, with efficiency near 40% under 500 sun AMI.5 illuminations. In partnership with The University of California Los Angeles (UCLA)

    Highly Mismatched GaSb-GaAs thin film Multijunction Solar Cells

    This purpose of this grant is to increase the efficiency of solar cells using highly mismatched, multi-junction (MJ) Sb-based solar cell with low defect density and optimal bandgap subcells, with efficiency near 40% under 500 sun AMI.5 illuminations.

    In partnership with The University of California Los Angeles (UCLA)

    This technology will allow for development of 4-6 junction III-V solar cells on Si substrates within a 3-5 year window. We propose to gain access to near optimal band gaps for a multijunction (MJ) solar cell by integrating Sb-based material into the InGaP2/GaAs technology using the interfacial misfit (IMF) growth technique pioneered by our team members [1, need reference]. In this ~ 1 year project, we began with 0.73 e V GaSb, which modeling predicts will yield nearly 35% under 1 sun. As our team members have already demonstrated, IMF growth will allow us to achieve the lattice-mismatched (LMM) growth of high quality GaSb on GaAs without the need for a complex and growth intensive step-grade buffer layer. If successful, this would result in an immediate 30% reduction in cost associated with the materials growth. As a longer term impact, the GaSb system would also allow four (or six) junction devices comprised of lattice matched InGaP2 and GaAs as the top cells, a single IMF transition and lattice matched AlGa(As)Sb and GaSb bottom cells, with potential for efficiency over 50% under moderate concentration. The addition of a second AlSb IMF layer would also allow the entire structure to be grown upright on a low cost silicon wafer. (Dept of Education)

  • Transition of High-Performance III-V Solar Cells to Low Cost Substrates

    Transition of High-Performance III-V Solar Cells to Low Cost Substrates

    The purpose of this grant is to radically reduce the cost of high-efficiency III-V solar cells by developing single-junction (SJ), polycrystalline (PX) GaAs and InP thin film solar cells on low cost metal foils. In partnership with Old Dominion University (ODU)

    Transition of High-Performance III-V Solar Cells to Low Cost Substrates

    The purpose of this grant is to radically reduce the cost of high-efficiency III-V solar cells by developing single-junction (SJ), polycrystalline (PX) GaAs and InP thin film solar cells on low cost metal foils.

    In partnership with Old Dominion University (ODU)

    The goal of this three-year program is to demonstrate thin-film PX-GaAs solar cells on low-cost substrates with efficiencies near 18%-20% grown by low cost, large area deposition techniques. These goals will be achieved by leveraging RIT’s experience in GaAs growth on poly-Ge and expertise in applying nano-technology approaches to enhancing GaAs solar cell performance, our demonstrated experience in GaAs grain boundary passivation and demonstrated high-performance GaAs cells on large-grain Ge templates, and ODU’s array of physical vapor deposition equipment and materials science expertise. (Dept of Defense, Navy)

  • Strain Balanced Quantum Dots for High Concentration Solar Photovoltaics

    Strain Balanced Quantum Dots for High Concentration Solar Photovoltaics

    This CAREER award seeks to provide insight into the fundamental material aspects of using nanomaterials for application in high concentration photovoltaic (HCPV) systems.

    Strain Balanced Quantum Dots for High Concentration Solar Photovoltaics

    This CAREER award seeks to provide insight into the fundamental material aspects of using nanomaterials for application in high concentration photovoltaic (HCPV) systems.

    The goal of this project is to addresses the need for future high-efficiency solar cells for HCPV grid-tied solar farms. While there has been extensive theoretical work that indicates the benefits of nanostructures in enhancing solar cell efficiency, there remains a significant amount of fundamental materials development necessary for practical implementation. This includes, selecting the appropriate quantum confined material system; study of the growth and incorporation mechanisms of epitaxial nanostructures into solar devices and; relation of the optical and electrical results to theoretical predictions. Additionally, HCPV systems must operate under extreme conditions (50-80Co nominal operating temperature), thus evolution of degradation mechanisms in nanomaterials is a critical concern. Materials based topics to investigate include vapor phase epitaxial (VPE) growth and characterization of multi-layer stacks of quantum dots (InAs, InP and GaSb) using a dot-barrier strain balancing technique. Increasing the number of quantum dot layers is particularly important for increased QD absorption in solar cells but is also much broader in scope and is equally as important for QD based lasers and detectors. Analysis and demonstration of true wave function overlap and mini-band formation in quantum dot solar cells using both optical and electrical characterization. Study of degradation mechanisms in QD cells under variable environmental conditions. Emphasis will be on understanding the interplay between high quality VPE growth of the quantum dot, nanostructured solar cell optical and electrical characterization, fundamental quantum mechanical predictions and subsequent carrier transport mechanisms. This project will leverage existing programs in nanomaterials and solar cell development at the Rochester Institute of Technology NanoPower Research Labs (NPRL) and NASA Glenn Research Center in order to address the above goals.(NSF)

  • Nano-Structured Photovoltaics and Optoelectronics

    Nano-Structured Photovoltaics and Optoelectronics

    These funds purchased a toolset, consisting of a LayTec EpiCurveTT that will measure materials’ reflectivity, composition and stain in-situ during MOVPE growth, a Nanometrics RPM Blue photoluminescence mapping tool and Electrochemical Capacitance Voltage Profiler to correlate ex-situ the materials bandgap, alloy composition, doping and defect profiles. These tools will enable the research in novel materials systems for both photovoltaics and infrared optoelectronic devices.

    Nano-Structured Photovoltaics and Optoelectronics

    (Dept of Defense/ Navy)

    These funds purchased a toolset, consisting of a LayTec EpiCurveTT that will measure materials’ reflectivity, composition and stain in-situ during MOVPE growth, a Nanometrics RPM Blue photoluminescence mapping tool and Electrochemical Capacitance Voltage Profiler to correlate ex-situ the materials bandgap, alloy composition, doping and defect profiles. These tools will enable the research in novel materials systems for both photovoltaics and infrared optoelectronic devices. The toolset will allow RIT the capacity to measure both in-situ and ex-situ the strain, bandgap and material quality of novel materials grown using our newly acquired metal organic vapor phase epitaxy (MOVPE) tool. The toolset will be devoted to development of 111-V nanostructured devices and materials for power generation, energy harvesting and adaptive multimodal sensing. Applications of interest to DoD include high-efficiency nanostructured photovoltaics, radioisotope power generation, 111-V on Si photovoltaics and Optoelectronics, and long wavelength infrared detectors. This combined toolset, when used with the existing RIT MOCVD facility, will give the PIs unprecedented characterization capability to rapidly develop the new materials and devices that are of interest to our DoD sponsor agencies. The equipment will be installed in our state of the art 10,000 sq. ft. cleanroom facility and will provide for unmatched uniformity, control and materials utilization efficiency.

  • Development of InAlAs Top Cell for High Specific Power Multijunction Photovoltaics

    Development of InAlAs Top Cell for High Specific Power Multijunction Photovoltaics

    Development of InAlAs to improve upon current space photovoltaics (PV). Development of InAIAs for engineered substrates would result in a lattice-matched triple-junction cell with a I-sun AMI.5 efficiency of 40.4%.

    Development of InAlAs Top Cell for High Specific Power Multijunction Photovoltaics

    (NASA)

    Development of InAlAs to improve upon current space photovoltaics (PV). Development of InAIAs for engineered substrates would result in a lattice-matched triple-junction cell with a I-sun AMI.5 efficiency of 40.4%. InAIAs lattice-matched to InP has the appropriate bandgap for operation in low-intensity low-temperature conditions.The InP materials system is known to be exceptionally radiation tolerant, which is ideal for space operation. Ultimately, this technology would increase capability and durability for missions and would also correspond to technology gains for terrestrial concentrator photovoltaic systems.

  • High Efficiency, Radiation Hard and Light Weight IMM Solar Cells

    High Efficiency, Radiation Hard and Light Weight IMM Solar Cells

    In this Phase II project, MicroLink and RIT, will incorporate quantum dots in the GaAs and InGaAs subcells of an InGaP/GaAs/InGaAs triple-junction solar cell to increase the radiation tolerance and thereby improve the end-of-life performance of the solar cell by >5%.

    High Efficiency, Radiation Hard and Light Weight IMM Solar Cells

    (NASA/ Microlink)

    In this Phase II project, MicroLink and RIT, will incorporate quantum dots in the GaAs and InGaAs subcells of an InGaP/GaAs/InGaAs triple-junction solar cell to increase the radiation tolerance and thereby improve the end-of-life performance of the solar cell by >5%. The quantum dot solar cell will be grown in an inverted metamorphic (IMM) format on GaAs and will be compatible with MicroLink’s epitaxial lift-off (ELO) process. The resulting solar cells will be lightweight, flexible, and radiation tolerant. Mechanically, they will resemble a sheet of thin metal foil. Innovative light management techniques such as reflective metal back contact and silver nanoparticle-enhanced reflectivity will be employed to increase absorption in the solar cell.

  • Tritium-Based Solid State Power Supplies

    Tritium-Based Solid State Power Supplies

    This initiative consists of the development of solid state photodiodes optimized for low-light levels to serve as the converter in an indirect conversion radioisotope battery.

    Tritium-Based Solid State Power Supplies

    (Dept of Defense/ EcoPulse)

    This initiative consists of the development of solid state photodiodes optimized for low-light levels to serve as the converter in an indirect conversion radioisotope battery. The indirect- conversion radioisotope battery consist of two parts: I) a combined tritium and phosphor capsule which converts the radiant energy of beta particles produced by the tritium gas into light and 2) a wide bandgap photodiode that converts the emitted light of the phosphor into energy. Dr. Seth Hubbard’s team at RIT will support the Army Research Laboratory through simulation, growth, measurement and characterization of wide bandgap photodetectors optimized for low light intensity ( 100-1000 n WI cm2) and with peak power conversion efficiency near 525 nm.

  • COLLABORATIVE RESEARCH: Highly Mismatched GaSb-GaAs Thin Film Multijuction Solar Cells for High Efficiency

    COLLABORATIVE RESEARCH: Highly Mismatched GaSb-GaAs Thin Film Multijuction Solar Cells for High Efficiency

    RIT and UCLA propose a program to study the interfacial misfit (IMF) growth technique as applied to highly mismatched, multi-junction (MJ) Sb-based solar cell. The broader goal of this program is to enable low defect density and optimal bandgap multi-junction solar cells, with efficiency near 50% under 500 sun AMI.5 illumination.

    COLLABORATIVE RESEARCH: Highly Mismatched GaSb-GaAs Thin Film Multijuction Solar Cells for High Efficiency

    (NSF EECS-1509468/ UCLA)

    RIT and UCLA propose a program to study the interfacial misfit (IMF) growth technique as applied to highly mismatched, multi-junction (MJ) Sb-based solar cell. The broader goal of this program is to enable low defect density and optimal bandgap multi-junction solar cells, with efficiency near 50% under 500 sun AMI.5 illumination. We propose to gain access to near optimal band gaps for a multijunction (MJ) solar cell by integrating Sb-based material into the InGaP2/GaAs technology using the IMF growth technique pioneered by our team members. IMF growth will allow us to achieve the lattice-mismatched (LMM) growth of high quality GaSb on GaAs without the need for a complex and growth intensive step-grade buffer layer. The GaSb system also allows four or six junction devices comprised of lattice matched InGaP2 and GaAs as the top cells, a single IMF transition and lattice matched AlGaSb and GaSb bottom cells, with potential for efficiency over 50% under moderate concentration. The addition of a second AlSb IMF layer may also allow the entire structure to be grown upright on a low cost silicon wafer.

Past Research Projects

  • Quantum Dot and Doping Super-lattice (nipi) Photovoltaic Devices

    Quantum Dot and Doping Super-lattice (nipi) Photovoltaic Devices

    This grant seeks to address the challenges and shed light on the technology and device physics of next generation quantum dot solar cells, leading to an intermediate band solar cell. In partnership with University of Toledo

    Quantum Dot and Doping Super-lattice (nipi) Photovoltaic Devices

    This grant seeks to address the challenges and shed light on the technology and device physics of next generation quantum dot solar cells, leading to an intermediate band solar cell.

    In partnership with University of Toledo

    One facet of the research will focus on Sb materials systems with improved bandgap and little valence band offset for the IBSC application. The other will focus on doping the superlattice nipi devices, which allow for longer carrier lifetime, improved absorption coefficients and high QD doping levels. The project team combines the state-of-the-art expertise in QD solar cell science and development at RIT with expertise in characterization of electronic properties at University of Toledo.

  • Development of III-Sb Quantum Dot Systems for High Efficiency Intermediate Band Solar Cells

    Development of III-Sb Quantum Dot Systems for High Efficiency Intermediate Band Solar Cells

    The objective of this project is to identify and develop a III-Sb based quantum dot (QD) system suitable for intermediate band solar cells (IBSC) via thorough theoretical and experimental analysis supported by sophisticated band structure modeling.

    Development of III-Sb Quantum Dot Systems for High Efficiency Intermediate Band Solar Cells

    (Dept of Energy/ University of California-Los Angeles)

    The objective of this project is to identify and develop a III-Sb based quantum dot (QD) system suitable for intermediate band solar cells (IBSC) via thorough theoretical and experimental analysis supported by sophisticated band structure modeling. Preliminary modeling results predict that III-Sb quantum dot solar cells (QDSC) can achieve efficiencies over 50%. Our final device demonstration is expected to meet all DOE-established review criteria and the overarching goal of $1/WPV system cost.

  • Multijunction Solar Cells Lattice-Matched to InP - A Path to High-Efficiency Flexible Photovoltaics

    Multijunction Solar Cells Lattice-Matched to InP - A Path to High-Efficiency Flexible Photovoltaics

    This grant supports Naval Research Laboratory’s mission to develop high-efficiency, flexible photovoltaics by developing a novel triple-junction solar cell structure lattice-matched to InP, comprised of a bandgap stack of 0.7/1.17/1.80 eV subcells.

    Multijunction Solar Cells Lattice-Matched to InP – A Path to High-Efficiency Flexible Photovoltaics 

    (Dept of Defense/ US Navy)

    This grant supports Naval Research Laboratory’s mission to develop high-efficiency, flexible photovoltaics by developing a novel triple-junction solar cell structure lattice-matched to InP, comprised of a bandgap stack of 0.7/1.17/1.80 eV subcells. This project will focus on the epitaxial material development of the novel materials within the triple junction solar cell. The low-bandgap cell will be epitaxial strain-compensated InGaAs/InGaAs quantum well/barrier structures. Ultimately, a path will be illustrated where in these materials and processes can be integrated with established epitaxial liftoff (ELO) technology to produce a thin, high specific power density, and flexible solar cell.

  • Radiation Hard Quantum Well Multijunction Solar Cells

    Radiation Hard Quantum Well Multijunction Solar Cells

    This project supports CFDRC by design, epitaxial growth, fabrication and testing of both standard and quantum well enhanced photovoltaic devices.

    Radiation Hard Quantum Well Multijunction Solar Cells 

    (Missile Defense A/CFD)

    This project supports CFDRC by design, epitaxial growth, fabrication and testing of both standard and quantum well enhanced photovoltaic devices. The effort concentrates on the design and demonstration of QW-enhanced middle cell having enhanced photovoltaic efficiency and radiation tolerance. The development of the middle cell technology by RIT will be subsequently transferred to a commercial epitaxial growth vendor to be incorporated into a triple-junction solar cell.

  • Quantum and Nano-Structure Enhanced Epitaxial Life-Off (ELO) Solar Cells

    Quantum and Nano-Structure Enhanced Epitaxial Life-Off (ELO) Solar Cells

    Photovoltaic power sources for space power generation applications must be high-efficiency, lightweight and radiation-hard. MicroLink along with the STTR partner RIT propose to meet these criteria with an innovative, high-efficiency QDs enhanced IB solar cells based on ELO technology.

    Quantum and Nano-Structure Enhanced Epitaxial Life-Off (ELO) Solar Cells

    (Dept of Defense/ Air Force/ Microlink)

    Photovoltaic power sources for space power generation applications must be high-efficiency, lightweight and radiation-hard. MicroLink along with the STTR partner RIT propose to meet these criteria with an innovative, high-efficiency QDs enhanced IB solar cells based on ELO technology. The proposed structure will achieve a much higher end-of-life power conversion efficiency, in conjunction with a greatly increased power density, than current state-of-the-art photovoltaic technologies. MicroLink’s proprietary epitaxial lift-off (ELO) process will be used to remove the substrate to produce ultra-lightweight, flexible, robust solar cells. Substrate reuse will render this GaAs-based approach cost-effective.