Gary Bulman - Academia.edu (original) (raw)

Papers by Gary Bulman

MRS Proceedings, 2011

ABSTRACTWe report on our investigation into the use of III-V superlattice structures for thermoel... more ABSTRACTWe report on our investigation into the use of III-V superlattice structures for thermoelectric (TE) applications. Preliminary review of III-V materials trends indicate that the GaSb/InAs superlattice system should offer one of the best potentials for high thermoelectric performance in the 500K-800K range. MOCVD growth of GaSb/InAs superlattice structures was carried out, and relevant structural, thermal, and electrical characterization has been performed. TEM and XRD results demonstrate a well-ordered superlattice structure. Thermal conductivity measurements reveal a reduction in the room-temperature thermal conductivity of GaSb/InAs superlattices (4.4-10.0 W/m-K), relative to either binary GaSb (32 W/m-K) or InAs (27 W/m-K). Additionally, we have worked to optimize the thermoelectric power factor (α2σ), studying both Se- and Te-doping of the superlattice structures, in an effort to demonstrate optimal thermoelectric performance. Our results demonstrate a maximum ZT of 0.36...

MRS Proceedings, 1999

We report on an experimental study of microstructure-based lasing in an optically pumped GaN/AlGa... more We report on an experimental study of microstructure-based lasing in an optically pumped GaN/AlGaN separate confinement heterostructure (SCH). We achieved low-threshold ultra-violet lasing in optically pumped GaN/AlGaN separate confinement heterostructures over a wide temperature range. The spacing, directionality, and far-field patterns of the lasing modes are shown to be the result of microcavities that were naturally formed in the structures due to strain relaxation. The temperature sensitivity of the lasing wavelength was found to be twice as low as that of bulk-like GaN films. Based on these results, we discuss possibilities for the development of ultra-violet laser diodes with increased temperature stability of the emission wavelength.

Journal of Vacuum Science & Technology A, 1998

ABSTRACT Changes in film morphology upon annealing Ni and Ni/Au contacts to GaN were examined usi... more ABSTRACT Changes in film morphology upon annealing Ni and Ni/Au contacts to GaN were examined using scanning electron microscopy and atomic force microscopy. Atomic force microscopy was performed on the GaN surface that was exposed by etching away the metal film. This technique was demonstrated to be a convenient and effective way to evaluate the morphology of the contact/semiconductor interface, rapidly providing spatial information in three dimensions. Metal island formation and a corresponding deep, nonuniform metal penetration into GaN were observed after annealing Ni/GaN and Au/Ni/GaN contacts above 800 and 700 °C, respectively. © 1998 American Vacuum Society.

Nature Communications, 2016

In present-day high-performance electronic components, the generated heat loads result in unaccep... more In present-day high-performance electronic components, the generated heat loads result in unacceptably high junction temperatures and reduced component lifetimes. Thermoelectric modules can, in principle, enhance heat removal and reduce the temperatures of such electronic devices. However, state-of-the-art bulk thermoelectric modules have a maximum cooling flux q max of only about 10 W cm À 2 , while state-of-the art commercial thin-film modules have a q max o100 W cm À 2. Such flux values are insufficient for thermal management of modern high-power devices. Here we show that cooling fluxes of 258 W cm À 2 can be achieved in thin-film Bi 2 Te 3-based superlattice thermoelectric modules. These devices utilize a p-type Sb 2 Te 3 /Bi 2 Te 3 superlattice and n-type d-doped Bi 2 Te 3 À x Se x , both of which are grown heteroepitaxially using metalorganic chemical vapour deposition. We anticipate that the demonstration of these high-cooling-flux modules will have far-reaching impacts in diverse applications, such as advanced computer processors, radio-frequency power devices, quantum cascade lasers and DNA micro-arrays.

J Electron Mater, 2009

Thin-film Bi2Te3-and Sb2Te3-based superlattice (SL) thermoelectric (TE) devices are an enabling t... more Thin-film Bi2Te3-and Sb2Te3-based superlattice (SL) thermoelectric (TE) devices are an enabling technology for high-power and low-temperature applications, which include low-noise amplifier cooling, electronics hot-spot cooling, radio frequency (RF) amplifier thermal management, ...

Aps March Meeting Abstracts, Mar 1, 1996

We have studied the optical properties of GaN epitaxial layers and GaN/AlGaN heterostructures (DH... more We have studied the optical properties of GaN epitaxial layers and GaN/AlGaN heterostructures (DH) grown on SiC substrates by MOCVD. A variety of spectroscopic methods including photoluminescence and photoreflectance measurements was used to study the optical transitions originated from the intrinsic free excitons and impurity-bound excitons. Transitions associated with the impurities and defects in the GaN active layer, as well

Energy Harvesting and Storage: Materials, Devices, and Applications II, 2011

Journal of Electronic Materials, 2014

ABSTRACT We used x-ray diffraction and transmission electron microscopy to study the mechanism of... more ABSTRACT We used x-ray diffraction and transmission electron microscopy to study the mechanism of thermal misfit strain relaxation in epitaxial Ge films grown on Si(001) substrates by the two-step growth technique. Lattice misfit strain associated with Ge/Si(001)Si mismatched epitaxy is largely relieved by a network of Lomer edge misfit dislocations during the first step of growth. However, thermal misfit strain during growth is relieved primarily by interdiffusion at the Si/Ge heterointerface. Two SiGe compositions containing 0.5 at.% and 6.0 at.% Si detected at the interface relieve thermal mismatch strain associated with the two growth steps. A thermodynamic model has been proposed to explain the state of strain in the films.

1984 International Electron Devices Meeting, 1984

A Be+implanted lateral In.2Ga.8As/GaAs SLS photodetector has been fabricated. The devices exhibit... more A Be+implanted lateral In.2Ga.8As/GaAs SLS photodetector has been fabricated. The devices exhibit good reverse bias characteristics with dark current of less than 6nA at -60 V. Quantum efficiency measurements indicate an uncoated external value of 50 percent at -20V. Position resolved photocurrent measurements show that carrier collection occurs over a large area (100µm × 250µm at -50V) with capacitance values

Energy Harvesting and Storage: Materials, Devices, and Applications V, 2014

Infrared Technology and Applications XXXVI, 2010

SiGe based Focal Plane Arrays offer a low cost alternative for developing visible-NIR focal plane... more SiGe based Focal Plane Arrays offer a low cost alternative for developing visible-NIR focal plane arrays that will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based IRFPA's will take advantage of Silicon based technology, that promises small feature size, low dark current and compatibility with the low power silicon CMOS circuits for signal processing. This paper discusses performance comparison for the SiGe based VIS-NIR Sensor with performance characteristics of InGaAs, InSb, and HgCdTe based IRFPA's. Various approaches including device designs are discussed for reducing the dark current in SiGe detector arrays; these include Superlattice, Quantum dot and Buried junction designs that have the potential of reducing the dark current by several orders of magnitude. The paper also discusses approaches to reduce the leakage current for small detector size and fabrication techniques. In addition several innovative approaches that have the potential of increasing the spectral response to 1.8 microns and beyond.