scispace - formally typeset
Search or ask a question
Author

Samuel Graham

Bio: Samuel Graham is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Thermal conductivity & Thermal resistance. The author has an hindex of 48, co-authored 347 publications receiving 9774 citations. Previous affiliations of Samuel Graham include Merck & Co. & United States Military Academy.


Papers
More filters
ReportDOI
01 Feb 2004
TL;DR: In this article, a concurrent computational and experimental investigation of thermal transport is performed with the goal of improving understanding of, and predictive capability for, thermal transport in microdevices, and the experimental component involves steady-state measurement of thermal conductivity on silicon films as thin as 340nm at a range of temperatures.
Abstract: A concurrent computational and experimental investigation of thermal transport is performed with the goal of improving understanding of, and predictive capability for, thermal transport in microdevices. The computational component involves Monte Carlo simulation of phonon transport. In these simulations, all acoustic modes are included and their properties are drawn from a realistic dispersion relation. Phonon-phonon and phonon-boundary scattering events are treated independently. A new set of phonon-phonon scattering coefficients are proposed that reflect the elimination of assumptions present in earlier analytical work from the simulation. The experimental component involves steady-state measurement of thermal conductivity on silicon films as thin as 340nm at a range of temperatures. Agreement between the experiment and simulation on single-crystal silicon thin films is excellent, Agreement for polycrystalline films is promising, but significant work remains to be done before predictions can be made confidently. Knowledge gained from these efforts was used to construct improved semiclassical models with the goal of representing microscale effects in existing macroscale codes in a computationally efficient manner.

6 citations

01 Jan 2005
TL;DR: In this article, the heat dissipation in GaN devices grown on low thermal conductivity lithium gallate (LGO) substrates was investigated using a phonon transport model which included dislocation density and temperature dependence.
Abstract: The heat dissipation in GaN devices grown on low thermal conductivity lithium gallate (LGO) substrates was inves- tigated. The thermal conductivity of single-crystal LGO was mea- sured utilizing the technique for temperatures ranging from 100 K-500 K. For the GaN layer, the thermal conductivity was esti- mated using a phonon transport model which included dislocation density and temperature dependence. These data were then used in a finite element program to determine the thermal behavior of a heterojunction field-effect transistor. Based on a maximum junc- tion temperature of 500 K, it was found that devices with a power dissipation of 1 W/mm were possible if the primary heat dissipation path was through the low thermal conductivity substrate. However, in using a front side cooling scheme, results suggest that it may be possible to develop devices with power dissipation in the range of 10 W/mm.

6 citations

Proceedings ArticleDOI
TL;DR: In this paper, the temperature distribution of a dual multi-quantum well (MQW) light emitting diode (LED) has been investigated using both infrared imaging and micro-Raman Spectroscopy; mean values over the device yielded temperatures ranging from 30-75°C.
Abstract: The temperature distribution of a dual Multi-Quantum Well (MQW) light emitting diode (LED) has been investigated using both infrared imaging and micro-Raman Spectroscopy; mean values over the device yielded temperatures ranging from 30-75°C. The InGaN/GaN based LED, grown by Metal Organic Chemical Vapor Deposition (MOCVD), was also studied using the 3ω method in order to determine an effective thermal conductivity of the MQW stack in the temperature range from 300-540K. The LED structure under investigation showed effective thermal conductivities in the range from 82-140 W/mK with the peak conductivity occurring at 440K, well above room temperature. Using temperature dependent properties determined experimentally, a numerical model of the LED structure was developed in order to study the effect that the package thermal resistance and input power has on the temperature of the device.

6 citations

Journal ArticleDOI
TL;DR: In this article, the authors report on phonon scattering processes and thermal conductivity in Al1-xScxN alloys grown by molecular beam epitaxy with the Sc content (x) up to 0.26.

5 citations

Book ChapterDOI
01 Jan 2021
TL;DR: In this article, the anisotropic thermal conductivity of β-Ga2O3 and the thermal boundary conductance between the transistors and metal contacts are investigated. And different device architectures and cooling strategies can be used to improve heat dissipation, namely cooling from the bottom side, top side, or double side cooling of field effect transistors.
Abstract: β-Ga2O3 is a promising ultrawide bandgap semiconductor under development for power electronics and RF applications. However, the low thermal conductivity of β-Ga2O3 presents challenges for creating high power devices and managing the thermal loads without exceeding thermal limits. In this chapter, we cover the anisotropic thermal conductivity of β-Ga2O3 and the anisotropic thermal boundary conductance between β-Ga2O3 and metal contacts. These properties play a major role in the way devices dissipate heat. Next, these properties are used to explore how different device architectures and cooling strategies can be used to improve heat dissipation, namely cooling from the bottom side, top side, or double side cooling of β-Ga2O3 field-effect transistors.

5 citations


Cited by
More filters
Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

Journal ArticleDOI
01 Aug 2014-Science
TL;DR: Perovskite films received a boost in photovoltaic efficiency through controlled formation of charge-generating films and improved current transfer to the electrodes and low-temperature processing steps allowed the use of materials that draw current out of the perovskites layer more efficiently.
Abstract: Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

5,789 citations

Journal ArticleDOI
TL;DR: A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized.
Abstract: A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion effi ciencies of up to 6.8%, a record for fullerene-free PSCs.

3,048 citations