Frequency domain thermoreflectance (FDTR) is used to create quantitative maps of thermal conductivity and thickness for a thinning gallium nitride (GaN) film on silicon carbide (SiC). GaN was grown by molecular beam epitaxy on a 4H-SiC substrate with a gradient in the film thickness found near the edge of the chip. The sample was then coated with a 5 nm nickel adhesion layer and a 85 nm gold transducer layer for the FDTR measurement. A piezo stage raster scans the sample to create phase images at different frequencies. For each pixel, a periodically modulated continuous-wave laser (the red pump beam) is focused to a Gaussian spot, less than 2 um in diameter, to locally heat the sample, while a second beam (the green probe beam) monitors the surface temperature through a proportional change in the reflectivity of gold. The pump beam is modulated simultaneously at six frequencies and the thermal conductivity and thickness of the GaN film are extracted by minimizing the error between the measured probe phase lag at each frequency and an analytical solution to the heat diffusion equation in a multilayer stack of materials. A scanning electron microscope image verifies the thinning GaN. We mark the imaged area with a red box. A schematic of the GaN sample in our measurement system is shown in the top right corner, along with the two fitting properties highlighted with a red box. We show the six phase images and the two obtained property maps: thickness and thermal conductivity of the GaN. Our results indicate a thickness dependent thermal conductivity of GaN, which has implications of thermal management in GaN-based high electron mobility transistors.
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Mapping Thickness Dependent Thermal Conductivity of GaN
Elbara Ziade,
Elbara Ziade
Department of Mechanical Engineering, Boston University, Boston, MA USA
eziade@bu.edu
eziade@bu.edu
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Jia Yang,
Jia Yang
Department of Mechanical Engineering, Boston University, Boston, MA USA
yangjia@bu.edu
yangjia@bu.edu
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Gordie Brummer,
Gordie Brummer
Department of Electrical and Computer Engineering, Boston University, Boston, MA USA
gbrummer@bu.edu
gbrummer@bu.edu
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Denis Nothern,
Denis Nothern
Division of Material Science and Engineering, Boston University, Boston, MA USA
dnothern@bu.edu
dnothern@bu.edu
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Theodore Moustaks,
Theodore Moustaks
Department of Electrical and Computer Engineering, Boston University, Boston, MA USA;
Division of Material Science and Engineering, Boston University, Boston, MA USA
tdm@bu.edu
tdm@bu.edu
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Aaron Schmidt
Aaron Schmidt
Department of Mechanical Engineering, Boston University, Boston, MA USA;
Division of Material Science and Engineering, Boston University, Boston, MA USA
schmidt@bu.edu
schmidt@bu.edu
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Elbara Ziade
Department of Mechanical Engineering, Boston University, Boston, MA USA
eziade@bu.edu
eziade@bu.edu
Jia Yang
Department of Mechanical Engineering, Boston University, Boston, MA USA
yangjia@bu.edu
yangjia@bu.edu
Gordie Brummer
Department of Electrical and Computer Engineering, Boston University, Boston, MA USA
gbrummer@bu.edu
gbrummer@bu.edu
Denis Nothern
Division of Material Science and Engineering, Boston University, Boston, MA USA
dnothern@bu.edu
dnothern@bu.edu
Theodore Moustaks
Department of Electrical and Computer Engineering, Boston University, Boston, MA USA;
Division of Material Science and Engineering, Boston University, Boston, MA USA
tdm@bu.edu
tdm@bu.edu
Aaron Schmidt
Department of Mechanical Engineering, Boston University, Boston, MA USA;
Division of Material Science and Engineering, Boston University, Boston, MA USA
schmidt@bu.edu
schmidt@bu.edu
1Corresponding author.
J. Heat Transfer. Feb 2016, 138(2): 020906
Published Online: January 18, 2016
Article history
Received:
November 6, 2015
Revised:
December 2, 2015
Citation
Ziade, E., Yang, J., Brummer, G., Nothern, D., Moustaks, T., and Schmidt, A. (January 18, 2016). "Mapping Thickness Dependent Thermal Conductivity of GaN." ASME. J. Heat Transfer. February 2016; 138(2): 020906. https://doi.org/10.1115/1.4032234
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