Selective Area Epitaxy on Foreign Substrates
The growth of various nanostructures, including nanowires and nanofins, by metal-organic chemical vapor deposition (MOCVD) is investigated through a unique crystal synthesis process known as selective area epitaxy (SAE). The SAE method relies on an oxide template with predefined windows that specify the location of preferential epitaxial atomic assembly. Growth rate enhancement, as defined by the oxide template, allows for the controlled epitaxy of arrays of vertical, III-V compound semiconductor nanostructures without the use of foreign catalytic or seeding agents. Based on the SAE technique, the EINS lab has demonstrated growth of InAs, InGaAs, GaAs, GaAsP, and GaP nanowire and nanofin arrays on Si substrates with 100% yield over large, wafer-scale areas. Our current projects aim to understand the growth kinetics of III-V nanosystems interfaced with Si and 2-dimensional nanomaterials such as graphene and monolayer transition metal dichalcogenides; to characterize the novel material properties offered by these hybrid nanosystems; and to demonstrate their utility in innovative photovoltaics and optoelectronics solutions.
MacEtch of III-V Compounds Using Alternative Catalysts
Metal-assisted chemical etching (MacEtch) is an anisotropic, solution-based nanofabrication process that combines the benefits of conventional wet-etching and plasma-based ion etching. The MacEtch process relies on site-specific, catalytic oxidation of a semiconductor surface by a patterned noble metal layer, followed by preferential dissolution of the selectively oxidized regions. Continuous repetition of oxidation-dissolution cycles in a single MacEtch bath results in the metal layer sinking into the semiconductor such that vertical nanostructures are left in the path of the metal layer, having geometries that are complementary to the geometry of the patterned metal. In the EINS lab, we are interested in exploring the fabrication of III-V semiconductor nanostructures using non-conventional metallic catalysts composed of carbon-nanotubes and graphene. In this manner we define novel nanofabrication paradigms that enable low-cost and clean alternatives to conventional ion-based etching procedures, offering high-aspect ratio features with atomically-abrupt sidewall termination. Novel device applications in high-efficiency solid-state lighting and tri-gated nanofin-based field effect transistors have already been demonstrated using on MacEtch fabrication.
Cosmic Radiation Damaged Image Repair project (CRDIR)
RIT has embarked on the Cosmic Radiation Damaged Image Repair project (CRDIR) involving Dr. Donald Pettit, NASA Astronaut & International Space Station astrophotographer. This project is being conducted by graduate and undergraduate student researchers under the guidance of Dr. Donald Figer, Director of CfD.
Students will have a unique opportunity to communicate with an active American astronaut in the process of solving a significant image processing issue. The scientific process these students will follow toward a solution will provide valuable experience that these students will carry with them in their professional lives.
RIT will be providing a sophisticated “image enhancement” software program which specifically addresses degraded images taken by astronauts “on orbit”, extending the useful lives of cameras, and in many cases making unacceptable “noisy” images visually acceptable.
Characterization of Inter-Pixel Capacitive Coupling in Hybridized HgCdTe Arrays
Inter-Pixel Capacitance (IPC) is a mechanism for deterministic electronic cross talk that results from coupling fields between adjacent pixels as a signal is collected and stored. Simulation of small arrays from first principles using software which simultaneously solves Poisson's equation and the Drift Diffusion equations allows for characterization of this coupling across a broad range of design parameters as well as across various environment parameters. Due to the deterministic nature of this cross-talk characterization results in correction.
This project is currently working on characterization of HgCdTe arrays hybridized using indium bumps to H2RG readout circuits akin to those to be used in the James Webb Space Telescope's (JWST) NIRcam. Successful characterization across environment parameters will result in an increase in final image quality from JWST's NIRcam and any device using a similar detector while also introducing new design considerations for future generations of sensor.
Development of Si-MOSFET CMOS Technology for Terahertz Detection
RIT is developing a silicon MOSFET CMOS imager to detect terahertz (THz) frequencies in a collaboration with the Center for Emerging and Innovative Sciences (CEIS) at the University of Rochester and Exelis Geospatial Systems. Creating an asymmetrical design within the FETs, increases the THz response. The current device being tested was designed with 15 individual test transistors with varying design dimensions and antennas along with an array of transistors for an imager. These test structures are being evaluated at RIT to determine the best design for terahertz detection for future imager designs. An advantage of this detector technology is that these MOSFETs will not have to be cooled to extreme temperatures like microbolometers. This project will advance knowledge of the detection mechanism, lead to the creation of an integrated imaging system, and has many different applications.
THz frequencies have been largely unexplored due to high absorption within water, however there has been an increase in interest with the rise in high-altitude and space-based telescopes. Emission lines in spectra within the THz regime exhibit cool molecular gas which traces protoplanetary disks and star formation rates within galaxies. This technology will also have other applications within the medical and security fields because of the non ionizing, non-harmful nature of THz radiation.
Phase II: New Infrared Detectors for Astrophysics
This program will have a profound impact across ground-based and space-based astronomy by dramatically reducing the cost of infrared detectors for existing facilities, as well as the next generation of extremely large telescopes. The project will continue development of a new material system for use in astronomical infrared array detectors. The devices use HgCdTe grown on Silicon using Molecular Beam Epitaxy. In Phase I of this project, the NSF ATI program funded two cycles of design, fabrication, and testing. The devices made in this phase of the project show that the technology will be successful for astronomy requirements pending further development. Testing shows that there are several challenges that prevent the devices in hand from satisfying these requirements. In this second phase, the effort will develop a series of devices with improved design and processing. The approach is to reduce the number of material defects while maintaining high short-wavelength quantum efficiency by using proven designs. Given that these previous designs have successfully been used to address the observed non-idealities, it is believed that the new activities will be successful. The work includes: growth of new material using a thick buffer layer design, fabrication of twelve FPAs in two designs, and extensive testing between the fabrication of the two designs.
This project will advance the knowledge of a material system that has great promise for infrared detector technology. It will enhance the capabilities of infrared instrumentation in astronomy by reducing cost and potentially improving performance when compared to what is available with existing technology. The technical approach has great merit because it was developed over the past 15 years and during Phase I of the project. The plan features a tight connection between design at Raytheon Vision Systems (RVS) and testing in the Center for Detectors at the Rochester Institute of Technology, continuing over 15 years of collaboration between RVS and the PI.
Single Photon Counting Detectors for NASA Astronomy Missions
Single photon counting detectors have the potential to be the next big advancement for NASA astronomy missions. The ability to count single photons facilitates science goals that are impossible even with current state-of-the-art detectors. Single photon counting detectors are the future, and many different implementations are in development. In the next 20 years, many NASA missions requiring single photon counting will be proposed, but which single photon counting detector implementations best suit the performance needs of NASA’s astronomy programs? The goal of the proposed research is to characterize (theoretically and physically) three unique implementations of single photon counting detectors, benchmark their operation over a range of performance characteristics, and provide comprehensive justification for the superiority of one of the implementations for each of these NASA astronomy applications: exoplanet detection, high-contrast imaging, adaptive optics, and array-based LIDAR.
The research plan in this project includes simulation, characterization, and evaluation of the performance of three types of semiconductor photon counting detectors for use in NASA astronomy missions: Geiger-mode (GM) APDs, linear-mode (LM) APDs, and Electron Multiplying (EM) CCDs.
The main goal of this project is to provide the basis of comparisons for several types of fundamentally different single photon counting detectors by producing a table of comparisons and recommendations for various applications. All detectors must be sensitive to single photons, be scalable to large array formats, and have high QE (in the visible, UV, NIR, IR, and Far-IR wavelengths). This research will advance preliminary work by adding new characterization methods and performance benchmarks, and by comparing the different devices at predetermined milestones during the project. The recommended detector(s) should function well at high readout frequencies without significant read noise (leading to improved temporal sampling), have very low noise for increased SNR at low fluence levels, and be implemented (or able to be in the near future) on large arrays. Even though single-photon counting detectors share a common performance benchmark (discerning individual quanta), differences between various implementations make some more efficient than others.
New Infrared Detectors for Astrophysics
Infrared arrays with HgCdTe as the light-sensitive layer, such as have been developed up to sizes 2048x2048 pixels for the James Webb Space Telescope, are near-ideal detectors for imaging and spectroscopy in the region ~1-5 microns. However current construction requires fabrication on CdZnTe substrates, which are expensive and limited in availability. The key to making larger (up to 14,000x14,000 pixels) and less expensive infrared detectors lies in using silicon wafer substrates, since large silicon wafers are common in the high volume semiconductor industry and their coefficient of thermal expansion is well-matched to that of the silicon readout circuits.
While the use of silicon substrates has been a major goal in the field of developing infrared detectors, the main limitation over the past 15 years has been the large lattice spacing mismatch between silicon and commonly-used infrared light-sensitive materials. The mismatch causes defects that can result in higher dark current, or valence holes that lead to reduced quantum efficiency and image persistence.
Enlisting the expertise and fabrication capabilities of Raytheon Vision Systems, detector expert Dr. D. Figer of the Rochester Institute of Technology plans to deposit the HgCdTe light-sensitive layer on silicon using the very promising technique of Molecular Beam Epitaxy (MBE). By maintaining vacuum during MBE processing, defect density has been shown to be reduced and the resulting prototype devices have achieved the anticipated performance. Very large, affordable infrared arrays will be essential for making optimum use of the proposed ~30m class ground-based telescopes and their availability has clear implications for fields beyond astronomy, including medical imaging and remote sensing.
A Zero Read Noise Detector for Thirty Meter Telescope (TMT)
The key objective of this project is to develop a new type of imaging detector that will enable the most sensitive possible observations with the world’s largest telescopes, i.e. the TMT. The detector will effectively quadruple the collecting power of the TMT, compared to detectors currently envisioned in TMT instrument studies, for the lowest light level observations. It would have fundamental importance in ground-based and space-based astrophysics, Earth and planetary remote sensing, exo-planet identification, consumer imaging applications, and homeland safety, among many others. Measurable outcomes include being able to see further back into the infancy of the Universe to taking a better picture (less grainy) of a smiling child blowing out the candles at her birthday party. The detector will be quantum-limited (zero read noise), be resilient against the harsh effects of radiation in space, consume low power, operate over an extremely high dynamic range, and be able to operate with exposure times over one million times faster than typical digital cameras. The RIDL is teaming with MIT/Lincoln Laboratory to leverage their Geiger-mode Avalanche Photodiode technology for developing the imaging detector. The project is funded through the Gordon and Betty Moore Foundation.
A Photon Counting Detector for Exoplanet Missions
The objective of this project is to advance photon-counting detectors for NASA exoplanet missions. A photon counting detector will provide zero read noise, ultra-high dynamic range, and ideal linearity over the relevant flux range of interest. It could be the best realizable detector for a planet finding spectrograph, and it would have outstanding properties as a wavefront sensor or detector in the imaging focal plane. The benefit of this device is that it will dramatically improve sensitivity beyond what is capable with non-photon counting detectors, thereby increasing science return for a fixed mission life; for low-light-level cases, such as spectroscopy, the device will reduce the necessary exposure time for detecting planetary features by 50-80%. The device always operates in photon counting mode and is thus not susceptible to excess noise factor that afflicts other technologies. It continues operating with shot-noise limited performance up to extremely high flux levels. Its performance is expected to be maintained at a high level throughout mission lifetime in the presence of the expected radiation dose.
LIDAR Imaging Detector
In collaboration with MIT/Lincoln Laboratory, the RIDL is developing an imaging Light Detection and Ranging (LIDAR) detector for NASA planetary space misisons. The device will have a pixelated array of independent Geiger-mode Avalanche Photodiodes that can asynchronously measure laser light time of flight. The output will be three-dimensional images providing distance measurements for each pixel. The device will have a timing accuracy of ~100 picoseconds, thus enabling a ranging accuracy ~1 cm, or roughly two orders of magnitude better than existing LIDAR instruments.
The nature of GLIMPSE 81: a star cluster to rival Westerlund 1
This project uses Chandra/ACIS observations of a young star cluster. The X-ray emission from this cluster, already observed in previous low-resolution observations, will be resolved by Chandra into many components. Analysis will include separation of the diffuse X-ray emission from the point-sources, and a spectral analysis of each source. The data from this project will be combined with those from other observations in order to perform a multiwavelength analysis.
Clumping in OB-star winds
Massive stars, their nature and evolution, play a important role at all stages of the Universe. Through their radiatively driven winds they influence on the dynamics and energetics of the interstellar medium. The winds of OB stars are the most studied case. Commonly, the mass-loss rates of luminous OB stars are inferred from several types of measurements, the strengths of UV P Cygni lines, H-alpha emission and radio and FIR continuum emission. Recent evidence indicates that currently accepted mass-loss rates may need to be revised downwards when small-scale density inhomogeneities (clumping) are taken into account. This project uses Herschel Space Telescope data to consistently treat ALL possible diagnostics, scanning different parts of the winds, and analyzed by means of ‘state of the art’ model atmospheres, will permit the determination of true mass-loss rates.
Guide Detector Evaluation for the Large Synoptic Survey Telescope (LSST)
The RIDL is testing prototype optical guide detectors for LSST. We have developed a guider testbed that simulates the expected image motion that the LSST focal plane will experience. The testbed will be used to validate guide detector performance against LSST requirements.
In collaboration with the University of Rochester, the RIDL is developing very low noise CMOS imaging detectors for NASA space astrophysics and planetary missions. These devices promise sub-electron read noise in a direct-readout architecture that is resilient against the transient and long-term effects of radiation. The novel readout circuit uses a one-bit sigma-delta oversampling comparator design developed by Zeljko Ignjatovic and Mark Bocko (University of Rochester). The light-sensitive silicon wafer is being designed and fabricated by RIDL and the RIT Semiconductor & Microsystems Fabrication Laboratory. NASA/JPL will delta-dope the backside of the detector for enhanced ultraviolet sensitivity. The wafer and the readout will be bump bonded together to produce a hybrid detector with good sensitivity from the ultraviolet through near-optical infrared.
A NICMOS survey of newly-identified young massive clusters
We are on the cusp of a revolution in massive star research triggered by 2MASS and Spitzer/GLIMPSE, and now is the ideal time to capitalize on these projects by performing the first survey of massive stars in young stellar clusters throughout the Galactic plane. A search of the 2MASS and GLIMPSE surveys has produced over 450 newly-identified massive stellar cluster candidates in the Galactic plane which are hidden from our view at optical wavelengths due to extinction. In this project, we are using 29 HST orbits to image the most promising candidate clusters in broad and narrow band filters using NICMOS. The observations will be complemented with approved Spitzer and Chandra programs, numerous approved and planned groundbased spectroscopic observations, and state-of-the-art modelling. We expect to substantially increase the numbers of massive stars known in the Galaxy, including main sequence OB stars and post-main sequence stars in the Red Supergiant, Luminous Blue Variable and Wolf-Rayet stages. Ultimately, this program will address many of the fundamental topics in astrophysics: the slope to the initial mass function (IMF), an upper limit to the masses of stars, the formation and evolution of the most massive stars, gamma-ray burst (GRB) progenitors, the chemical enrichment of the interstellar medium, and nature of the first stars in the Universe.
Mid-Infrared Spectroscopy of the Most Massive Stars
The most massive star that can form is presently defined by observations of a class of very rare stars having inferred initial masses of ~200 solar masses. There are only a few such stars in the Galaxy, including the Pistol Star, FMM362, and LBV 1806-20, the first two being located near the Galactic center, and third located in the disk near W31. Each has only recently been identified as so massive within the past 10 years through the analysis of infrared observations, but they are otherwise too faint, due to extinction, to observe at shorter wavelengths. These stars appear to be very luminous (L>10^6.3 solar luminosities), "blue" (T>10000 K), and variable (delta K~1 mag.), and the Pistol Star has ejected 10 solar masses of material in the past 10000 years. In addition, these stars have near-infrared spectra similar to those of prototypical Luminous Blue Variables, i.e. Eta Car and AG Car. Given their apparent violation of the Humphries-Davidson limit, they are presumably in a short-lived phase of stellar evolution that is often associated with rapid mass-loss through episodic eruptions of their outer atmospheres. We propose to determine the physical properties of these stars and the velocity and ionization structure in their winds by using spectra obtained with the high resolution modes of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The 10 to 40 micron wavelength region is ideally suited for accessing a variety of lines from transitions of hydrogen, helium, iron, silicon, sulfur, among others; indeed, through our models, we predict that sufficiently sensitive spectra will yield over 300 spectral lines. In addition, we predict that the mid-infrared continuum will be dominated by free-free emission generated in the thick winds associated with these stars, an effect that should be clearly detectable in the spectra.
Sandia FPGA Imaging Acquisition Software Development
RIDL developed HDL (Hardware Description Language) software for a FPGA (Field Programmable Gate Array) evaluation board for Sandia National Laboratories. The HDL software programs the FPGA chip to transfer digital video rate image data from the evaluation board to a windows based PC using the Camera Link data transfer format. Once the Camera Link data format became available, data acquisition software for the PC was developed to capture and display the imagery on the PC.
The Pre-Supernova Mass-Loss Behavior of Red Supergiants
The mass lost by massive stars as they pass through the Red Supergiant (RSG) phase is a crucial determinant in the terminal mass of the star, the nature of the resulting supernova explosion and the stellar end-state. However, up until now studies of this quantity have been problematic, owing to the low numbers of known RSGs and the difficulty of observing in the mid-IR. Here, we capitalize on the recent discoveries of two remarkable Galactic clusters containing unprecedented numbers of RSGs, and use the capabilities of Spitzer to undertake a comprehensive and unique study of the pre-SN mass-loss of massive stars. We will use Spitzer/IRS observations in conjunction with state-of-the-art dust models to provide the first quantitative investigation of the mass and composition of the pre-SN ejecta as a function of age and metallicity. This study is vital in determining the mass-loss behaviour of RSGs in particular, and the nature of supernova progenitors in general.
A Very Low Noise CMOS Detector Design for NASA
The purpose of this project is to design, fabricate, and test a novel new detector having many advantages over present CCD and CMOS devices. The hybrid CMOS detector is expected to have low noise, radiation tolerance, low power dissipation, low mass and robust electronics. Its low noise is derived from a novel on-die digitization circuit based on a sigma-delta feedback loop.
The Most Massive Stars
Until the Spitzer Space Telescope, there was no wide area survey that could identify massive stars at all distances in the Galaxy. Indeed, the sample of known O-stars is woefully incomplete, as it has largely been generated using optical observations that suffer from the absorption produced by dust in the disk. We will find and measure the physical properties of the most massive stars in the Galaxy using HST, Spitzer, Chandra, SOFIA, and ground-based observatories, using a survey technique that probes the majority of the Galaxy. This program addresses fundamental questions whose answers are basic requirements for studying many of the most important topics in Astrophysics: the formation and evolution of the most massive stars, the effects of massive stars on lower mass protostellar/protoplanetary systems, gamma-ray burst progenitors, nature of the first stars in the Universe, chemical enrichment of the interstellar medium, Galactic gas dynamics, star formation in starbursts and merging galaxies (particularly in the early Universe). The results of our program will influence the science programs for future NASA projects, i.e. JWST, SOFIA, SIM, TPF-C, and TPC-I.