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Eden Prairie, MN, United States

Polyakov A.Y.,Institute of Rare Metals | Smirnov N.B.,Institute of Rare Metals | Kozhukhova E.A.,Institute of Rare Metals | Osinsky A.V.,Agnitron Technology Inc. | Pearton S.J.,University of Florida
Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures

Nominally undoped GaN films were grown by metalorganic chemical vapor deposition under three different conditions, namely (1) "standard" growth conditions with growth temperature of 1000 °C and growth rate of 1 μm/h, (2) slightly reduced growth temperature of 975 °C, and (3) standard temperature, but higher growth rate of 2.5 μm/h. The standard sample had a net donor density <1015 cm-3, while the two other samples were semi-insulating, with sheet resistivity ∼1014 Ω/square and the Fermi level pinned at Ec-0.8 eV for the low temperature growth and at Ec-0.9 eV for the high growth rate conditions. The photoconductivity spectra of both of these latter samples show the presence of centers with optical threshold near 1.35 eV commonly attributed to C interstitials and centers with optical threshold near 2.7-2.8 eV and 3 eV often associated with C-related defects. However, no signals that could be attributed to substitutional C acceptors and C donors were detected. Current relaxation spectroscopy revealed deep traps with activation energies 0.2, 0.25, 045, and 0.8 eV. Annealing at 800 °C increased the concentration of these traps. The changes in resistivity induced by annealing in the high-growth rate sample were much stronger than for the low-temperature sample. The authors also observed a strong suppression of the yellow luminescence band intensity in the "standard" sample after annealing, as opposed to a slight increase of this band intensity in the two semi-insulating samples. The role of compensation by native defects and by deep levels related to carbon in the observed changes is discussed. © 2013 American Vacuum Society. Source

Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 124.93K | Year: 2014

This project is directed to the development of low-loss, high power-density Aluminum Nitride (AlN)/Gallium Nitride (GaN) heterostructure based transistors for enabling high-efficiency solid state power amplifiers (SSPA) needed for advancing capabilities of future robotic and human exploration spacecraft. The AlN/GaN heterostructure is a particularly attractive system for switch-mode applications due to the extremely high charge density, high electron mobility, high intrinsic breakdown field, and physical thinness achievable and has seen widespread investigation toward solid-state amplifiers in the recent years. However, very few innovations have been proposed with this heterostructure despite its expansive capacity for various creative device concepts. A new patent-pending multichannel AlN/GaN Field Screening High Electron Mobility Transistor (FS-HEMT) design is described. Preliminary experimental results are presented validating design principles that will eliminate current collapse phenomenon at X- and Ka-band frequencies that has plagues traditional HEMT designs and will ultimately deliver a low-loss switch-mode device.

Agency: Department of Defense | Branch: Army | Program: STTR | Phase: Phase II | Award Amount: 999.04K | Year: 2014

This project address the fabrication of solar blind detectors from the MgZnO material system. Both MBE and MOCVD material growth techniques will be used for deposition of the required material layers. Simulation software we be used to aid in the design of the photodetector structure. Devices will be fabricated from the grown structures and their electrical and optical characteristics determined.

Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 150.00K | Year: 2013

This Small Business Innovation Research (SBIR) Phase I project addresses the development of a novel technique for improving the efficiency of ultraviolet (UV) light emitting devices (LEDs). The UV LED fabrication process typically includes deposition of thin semiconductor films onto substrates that can be fabricated into devices. Traditionally, during the deposition process impurities are added to the semiconductor films to obtain the desired electrical properties. The introduction of the impurities, however, produces defects in the semiconductor materials that can limit the efficiency of the devices. The technique proposed in this project will modify the deposition process of the semiconductor films in order to obtain the desired electrical properties without the use of intentional impurities. This has the potential of producing much more efficient light emitters. The proposed technique has the added advantage of producing material whose electrical properties are less sensitive to temperature, which can prove useful for many applications. The composition of the semiconductor materials investigated in this project can be modified to produce LEDs capable of emitting light from the ultraviolet to visible range. A successful project will lead to an enabling technology for development of novel, high efficiency LEDs.

The broader impacts/commercial potential of this project addresses the development of efficient light emitting semiconductor devices. Fundamental physical properties studied in this effort will enhance scientific and technological understanding of the nature of semiconductors. These advances may yield a new paradigm for functionalizing semiconductor materials for more efficient and higher performance optical and electronic devices. Possible applications for this technological advance include general room lighting, traffic lights, outdoor displays, automotive applications, water treatment, sterilization, and ultrahigh density optical storage systems. Moreover, the technique proposed in this work may lead to improvement in the performance of other microelectronic devices such as transistors, laser diodes, modulators and photodetectors. The proposed devices will enable unique high power and extreme temperature operation as the approach does not face the same limitations as currently used technology. Significant commercialization potential exists for the proposed technology on the basis of superior performing devices in the aforementioned categories.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 149.89K | Year: 2014

AlN is an attractive material for power electronics device applications due to its wide bandgap and resulting high electric breakdown field. One of the major challenges that need to be addressed to achieve full utilization of AlN for power electronics applications is the development of a doping strategy for both donors and acceptors. Ion implantation is a particularly attractive approach since it allows for selected-area doping of semiconductors due to its high spatial and dose control and its high throughput capability. Active layers in the semiconductor are created by implanting a dopant species followed by very high temperature annealing to reduce defects and thereby activate the dopants. Application of Multicycle Rapid Thermal Annealing (MRTA) has demonstrated excellent results for annealing high dose implanted GaN. This approach has excellent potential for application with AlN. An effection annealing technique is one of the key capbabilities currently lacking from AlN ion implantation technology. The application and thorough study of this process for AlN implanted materials is anticipated to provide a means for creating n- and p-type AlN with high impurity concentrations and with excellent recovery from implantation induced radiation damage. In Phase I AlN layers will be grown by metalorganic chemical vapor deposition and implanted with chemical species such as Si and Mg. Rigorous annealing studies will be performed and the resulting free carrier concentrations determined as a function of the annealing schedules. The result of Phase I will be demonstration of a semi-optimized annealing schedule for AlN implanted material. Additionally a thorough characterization of hole hopping conduction in acceptor degenerate AlN which occurs at high impurity concentrations. Phase II will focus on the application of these techniques for fabrication of high power electronic devices. Commercial Applications and Other Benefits: AlGaN alloys with high Al composition and AlN based electronic devices are attractive for high voltage, high temperature applications, including microwave power sources, power switches and communication systems. These wide bandgap devices have large potential markets for enhancing efficiency of power conversion in nearly all areas. Estimated market potential for wide bandgap devices is well into the billion $ range within the next several years. The ability to control conductivity of AlN will unlock the materials extraordinary properties for various high power device designs.

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