Epitaxial films of β-(AlxGa1−x)2O3, β-Ga2O3, and β-(InxGa1−x)2O3 were grown on (001) sapphire sub... more Epitaxial films of β-(AlxGa1−x)2O3, β-Ga2O3, and β-(InxGa1−x)2O3 were grown on (001) sapphire substrates via metalorganic chemical vapor deposition (MOCVD). The compositions of the films as determined from energy dispersive x-ray analysis (EDX) and x-ray photoelectron spectroscopy (XPS) results were XAl = 0.57 ± 0.05 and 0.76 ± 0.05 and XIn = 0.12 ± 0.05 and 0.21 ± 0.05. The optical bandgap was found to correspondingly vary between 6.0 ± 0.2 and 3.9 ± 0.1 eV, as a function of composition via XPS and UV–visible spectroscopy (UV–Vis). X-ray diffraction, scanning electron microscopy, and atomic force microscopy revealed the films to be highly-oriented 2¯01\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \left( {\bar{2}01} \right) $$\end{document}-epitaxial films with nanocrystalline domains. Schottky- and MSM-based solar-blind UV photodetectors were fabricated on the films and showed responsivities at 20 V varying from > 104 A/W for the Ga2O3 devices, > 103 A/W for the (AlxGa1−x)2O3 devices and > 102 A/W for the (InxGa1−x)2O3 devices. Modest shifts in wavelength selectivity corresponding with the changes in composition/bandgap were also measured. Time response measurements on Schottky and MSM detectors reveal rise and dwell times on the order of a minute, indicating the presence of photoconductive gain. Noise-equivalent powers were in the fW–pW regime with specific detectivities (D∗\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ D^{*} $$\end{document}) between 1010 and 1012 Jones. Scanning photocurrent maps display large photocurrent generation at the Schottky interface in the case of a β-Ga2O3 Schottky detector, whereas for an β-(InxGa1−x)2O3 MSM detector the photocurrent generation occurs in the device channel and at the Schottky interface.
ABSTRACTThe demonstration of photoluminescence (PL) and electroluminescence (EL) in nanostructure... more ABSTRACTThe demonstration of photoluminescence (PL) and electroluminescence (EL) in nanostructures of Si or Ge, such as those found in porous silicon, has significantly improved the prospects of all Si based photonic devices. While the physical mechanisms at work are still a subject of much study, it is clear that the luminescence is associated with the formation of nanometer or “quantum” sized particles. Further, it is clear that prototype NanoCrystal Displays (NCDs) and communication devices are being fabricated in these material systems. We report here on the electroluminescent properties of nanometer sized particles in an SiO2 host matrix, which were fabricated by LPCVD techniques. The films have demonstrated reproducible emission from well below 400 nm to well above 800 nm. We believe that dispersion effects of the nanocrystals can account for "white" light emission. The films have been characterized using PL, Raman, XRD, TEM, and SIMS. The nanocrystals are primarily ...
Compositionally graded Barium Strontium Titanate (BST) thin films were deposited by MOCVD on r-pl... more Compositionally graded Barium Strontium Titanate (BST) thin films were deposited by MOCVD on r-plane sapphire substrates with patterned platinum electrodes. Tunable parallel plate capacitors were fabricated using these films by ion-milling and photolithography. The capacitors show a tunability of 36% for an electric field of + 13V at a measurement frequency of 1 MHz. These tunable capacitors were integrated with
ABSTRACTZnO thin films are of interest for an array of applications, including: light emitters, p... more ABSTRACTZnO thin films are of interest for an array of applications, including: light emitters, photovoltaics, sensors and transparent contacts, among others. Production routes for ZnO include sputtering, MBE and MOCVD. This paper focuses on our efforts to produce a large scale MOCVD thin film production tool and the results obtained from the reactor. Specifically, we have constructed a tool with a 16” wafer carrier that uniformly deposits ZnO films on 38×2” wafers simultaneously. The reactor operates at low pressure (<0.1 Atmosphere) and through 700°C. High quality, uniform films have been deposited on an array of substrates. Al-doped films exhibited resisitivities in the 1×10-3 ohm-cm range and transmissivity greater than 80%. Film morphology and crystallinity are a function of process parameters. The large area oxide MOCVD reactor design challenges and results are summarized. Tool performance and ZnO thin film quality are reviewed, as well as preliminary ZnO contact performanc...
Chalcogenide Random Access Memory (C-RAM) has shown significant promise in combining the desired ... more Chalcogenide Random Access Memory (C-RAM) has shown significant promise in combining the desired attributes of an ideal memory, including: nonvolatility, fast read/write/erase speed, low read/write/erase voltage/power, high endurance, and radiation hardness. Current C-RAM production technology relies on sputtering to deposit the active chalcogenide layer. The sputtering process leads to difficulties in meeting requirements for device conformality (in particular – filling vias), film adherence, compositional control, wafer yield, and surface damage. Ultimately, a viable CVD manufacturing process is needed for high-density products to realize the full potential of C-RAM. In this work, we discuss the Metal-Organic Chemical Vapor Deposition (MOCVD) tool technology used to produce the films and report the materials properties of GeSbTe-based chalcogenide thin films grown in small research scale and in large production scale MOCVD reactors. Films were grown at low pressures at temperature...
ZnO is a wide bandgap (3.2 eV) semiconductor with potential application in LEDs, lasers, and tran... more ZnO is a wide bandgap (3.2 eV) semiconductor with potential application in LEDs, lasers, and transparent transistors, among other uses. These applications require uniform thickness, high quality materials (amorphous, poly- or single crystal), pinhole- and defect-free-single-and multilayer-conformal coatings. These attributes are generally best achievable by MOCVD. We have mounted a significant effort to develop automated MOCVD systems and process technologies for single and multicomponent oxides. The reactors use high speed rotation and are of a vertical orientation built to all metal UHV standards. We have demonstrated reactor scaled performance from 3” to 12” diameter depositions planes with modeling scales through 24” diameter. Metalorganics are used for zinc and dopant sources as well as dopant gases to optimize performance at low pressures. In this paper we will discuss our most recent results with epitaxial ZnO films, achievements in p-type doping, multilayer structures, and p...
Although semiconductor wires exhibit unique properties that would benefit a range of devices, imp... more Although semiconductor wires exhibit unique properties that would benefit a range of devices, implementation of as-grown wires in a device brings challenges, in particular, for those that require large volume (e.g. thermoelectric (TE) devices). Therefore, a post-growth assembly of sub-micrometer-scale wires into a centimeter-scale structure would open new module architecture. In this paper, TE devices in the form of pellet (~1cm diameter) made of aggregated silicon (Si) wires will be described. Numerous Si wires were assembled into a 3D network with dimensions defined by a quartz ampule. Power generation was demonstrated at operational temperatures ~80°C and the performance was generalized for higher operational temperatures ~800°C.
2011 International Symposium on Applications of Ferroelectrics (ISAF/PFM) and 2011 International Symposium on Piezoresponse Force Microscopy and Nanoscale Phenomena in Polar Materials, 2011
Abstract Two types of semiconductors, indium phosphide (InP) and silicon (Si), were separately gr... more Abstract Two types of semiconductors, indium phosphide (InP) and silicon (Si), were separately grown on polycrystalline copper foils with the presence of gold colloidal particles. InP was grown with and without carbon deposition by metal organic chemical vapor deposition, and Si was grown with and without plasma enhanced chemical vapor deposition of carbon. While InP and Si grew as films on untreated copper foils, they were found to grow in the form of nanowires when copper foils were pre-treated with carbon. Structural analysis revealed that the grown InP nanowires were polycrystalline. In contrast, the grown Si nanowires were found to have core–shell structures with a monocrystalline core and a polycrystalline shell. Further analysis suggested that graphene was formed on the copper foils during the carbon deposition. Therefore, we concluded that the presence of graphene promoted the growth of InP and Si in the form of nanowires. The demonstration of growing semiconductor nanowires on copper foils could be a new path to integrate semiconductor and metal to provide a unique material platform for a wide range of devices.
Epitaxial films of β-(AlxGa1−x)2O3, β-Ga2O3, and β-(InxGa1−x)2O3 were grown on (001) sapphire sub... more Epitaxial films of β-(AlxGa1−x)2O3, β-Ga2O3, and β-(InxGa1−x)2O3 were grown on (001) sapphire substrates via metalorganic chemical vapor deposition (MOCVD). The compositions of the films as determined from energy dispersive x-ray analysis (EDX) and x-ray photoelectron spectroscopy (XPS) results were XAl = 0.57 ± 0.05 and 0.76 ± 0.05 and XIn = 0.12 ± 0.05 and 0.21 ± 0.05. The optical bandgap was found to correspondingly vary between 6.0 ± 0.2 and 3.9 ± 0.1 eV, as a function of composition via XPS and UV–visible spectroscopy (UV–Vis). X-ray diffraction, scanning electron microscopy, and atomic force microscopy revealed the films to be highly-oriented 2¯01\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \left( {\bar{2}01} \right) $$\end{document}-epitaxial films with nanocrystalline domains. Schottky- and MSM-based solar-blind UV photodetectors were fabricated on the films and showed responsivities at 20 V varying from > 104 A/W for the Ga2O3 devices, > 103 A/W for the (AlxGa1−x)2O3 devices and > 102 A/W for the (InxGa1−x)2O3 devices. Modest shifts in wavelength selectivity corresponding with the changes in composition/bandgap were also measured. Time response measurements on Schottky and MSM detectors reveal rise and dwell times on the order of a minute, indicating the presence of photoconductive gain. Noise-equivalent powers were in the fW–pW regime with specific detectivities (D∗\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ D^{*} $$\end{document}) between 1010 and 1012 Jones. Scanning photocurrent maps display large photocurrent generation at the Schottky interface in the case of a β-Ga2O3 Schottky detector, whereas for an β-(InxGa1−x)2O3 MSM detector the photocurrent generation occurs in the device channel and at the Schottky interface.
ABSTRACTThe demonstration of photoluminescence (PL) and electroluminescence (EL) in nanostructure... more ABSTRACTThe demonstration of photoluminescence (PL) and electroluminescence (EL) in nanostructures of Si or Ge, such as those found in porous silicon, has significantly improved the prospects of all Si based photonic devices. While the physical mechanisms at work are still a subject of much study, it is clear that the luminescence is associated with the formation of nanometer or “quantum” sized particles. Further, it is clear that prototype NanoCrystal Displays (NCDs) and communication devices are being fabricated in these material systems. We report here on the electroluminescent properties of nanometer sized particles in an SiO2 host matrix, which were fabricated by LPCVD techniques. The films have demonstrated reproducible emission from well below 400 nm to well above 800 nm. We believe that dispersion effects of the nanocrystals can account for "white" light emission. The films have been characterized using PL, Raman, XRD, TEM, and SIMS. The nanocrystals are primarily ...
Compositionally graded Barium Strontium Titanate (BST) thin films were deposited by MOCVD on r-pl... more Compositionally graded Barium Strontium Titanate (BST) thin films were deposited by MOCVD on r-plane sapphire substrates with patterned platinum electrodes. Tunable parallel plate capacitors were fabricated using these films by ion-milling and photolithography. The capacitors show a tunability of 36% for an electric field of + 13V at a measurement frequency of 1 MHz. These tunable capacitors were integrated with
ABSTRACTZnO thin films are of interest for an array of applications, including: light emitters, p... more ABSTRACTZnO thin films are of interest for an array of applications, including: light emitters, photovoltaics, sensors and transparent contacts, among others. Production routes for ZnO include sputtering, MBE and MOCVD. This paper focuses on our efforts to produce a large scale MOCVD thin film production tool and the results obtained from the reactor. Specifically, we have constructed a tool with a 16” wafer carrier that uniformly deposits ZnO films on 38×2” wafers simultaneously. The reactor operates at low pressure (<0.1 Atmosphere) and through 700°C. High quality, uniform films have been deposited on an array of substrates. Al-doped films exhibited resisitivities in the 1×10-3 ohm-cm range and transmissivity greater than 80%. Film morphology and crystallinity are a function of process parameters. The large area oxide MOCVD reactor design challenges and results are summarized. Tool performance and ZnO thin film quality are reviewed, as well as preliminary ZnO contact performanc...
Chalcogenide Random Access Memory (C-RAM) has shown significant promise in combining the desired ... more Chalcogenide Random Access Memory (C-RAM) has shown significant promise in combining the desired attributes of an ideal memory, including: nonvolatility, fast read/write/erase speed, low read/write/erase voltage/power, high endurance, and radiation hardness. Current C-RAM production technology relies on sputtering to deposit the active chalcogenide layer. The sputtering process leads to difficulties in meeting requirements for device conformality (in particular – filling vias), film adherence, compositional control, wafer yield, and surface damage. Ultimately, a viable CVD manufacturing process is needed for high-density products to realize the full potential of C-RAM. In this work, we discuss the Metal-Organic Chemical Vapor Deposition (MOCVD) tool technology used to produce the films and report the materials properties of GeSbTe-based chalcogenide thin films grown in small research scale and in large production scale MOCVD reactors. Films were grown at low pressures at temperature...
ZnO is a wide bandgap (3.2 eV) semiconductor with potential application in LEDs, lasers, and tran... more ZnO is a wide bandgap (3.2 eV) semiconductor with potential application in LEDs, lasers, and transparent transistors, among other uses. These applications require uniform thickness, high quality materials (amorphous, poly- or single crystal), pinhole- and defect-free-single-and multilayer-conformal coatings. These attributes are generally best achievable by MOCVD. We have mounted a significant effort to develop automated MOCVD systems and process technologies for single and multicomponent oxides. The reactors use high speed rotation and are of a vertical orientation built to all metal UHV standards. We have demonstrated reactor scaled performance from 3” to 12” diameter depositions planes with modeling scales through 24” diameter. Metalorganics are used for zinc and dopant sources as well as dopant gases to optimize performance at low pressures. In this paper we will discuss our most recent results with epitaxial ZnO films, achievements in p-type doping, multilayer structures, and p...
Although semiconductor wires exhibit unique properties that would benefit a range of devices, imp... more Although semiconductor wires exhibit unique properties that would benefit a range of devices, implementation of as-grown wires in a device brings challenges, in particular, for those that require large volume (e.g. thermoelectric (TE) devices). Therefore, a post-growth assembly of sub-micrometer-scale wires into a centimeter-scale structure would open new module architecture. In this paper, TE devices in the form of pellet (~1cm diameter) made of aggregated silicon (Si) wires will be described. Numerous Si wires were assembled into a 3D network with dimensions defined by a quartz ampule. Power generation was demonstrated at operational temperatures ~80°C and the performance was generalized for higher operational temperatures ~800°C.
2011 International Symposium on Applications of Ferroelectrics (ISAF/PFM) and 2011 International Symposium on Piezoresponse Force Microscopy and Nanoscale Phenomena in Polar Materials, 2011
Abstract Two types of semiconductors, indium phosphide (InP) and silicon (Si), were separately gr... more Abstract Two types of semiconductors, indium phosphide (InP) and silicon (Si), were separately grown on polycrystalline copper foils with the presence of gold colloidal particles. InP was grown with and without carbon deposition by metal organic chemical vapor deposition, and Si was grown with and without plasma enhanced chemical vapor deposition of carbon. While InP and Si grew as films on untreated copper foils, they were found to grow in the form of nanowires when copper foils were pre-treated with carbon. Structural analysis revealed that the grown InP nanowires were polycrystalline. In contrast, the grown Si nanowires were found to have core–shell structures with a monocrystalline core and a polycrystalline shell. Further analysis suggested that graphene was formed on the copper foils during the carbon deposition. Therefore, we concluded that the presence of graphene promoted the growth of InP and Si in the form of nanowires. The demonstration of growing semiconductor nanowires on copper foils could be a new path to integrate semiconductor and metal to provide a unique material platform for a wide range of devices.
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Papers by Gary Tompa