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Size dictated thermal conductivity of GaN

Journal of Applied Physics

Bays, Nathan R.; Mcdonald, Anthony; Fuller, Elliot J.; Talin, Albert A.; Rost, Christina M.; Maria, Jon P.; Gaskins, John T.; Hopkins, Patrick E.; Allerman, Andrew A.

The thermal conductivity of n- and p-type doped gallium nitride (GaN) epilayers having thicknesses of 3-4 μm was investigated using time domain thermoreflectance. Despite possessing carrier concentrations ranging across 3 decades (1015-1018cm-3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends - and their overall reduction relative to bulk - are explained leveraging established scattering models where it is shown that, while the decrease in p-type layers is partly due to the increased impurity levels evolving from its doping, size effects play a primary role in limiting the thermal conductivity of GaN layers tens of microns thick. Device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.

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TYPE Journal Article YEAR 2016
DOIOSTIScopus

Self-Heating and Failure in Scalable Graphene Devices

Scientific Reports

Bays, Nathan R.; Shaffer, Ryan; Mcdonald, Anthony; Hamilton, Allister B.; Nogan, John; Ohta, Taisuke; Howell, Stephen W.

Self-heating induced failure of graphene devices synthesized from both chemical vapor deposition (CVD) and epitaxial means is compared using a combination of infrared thermography and Raman imaging. Despite a larger thermal resistance, CVD devices dissipate >3x the amount of power before failure than their epitaxial counterparts. The discrepancy arises due to morphological irregularities implicit to the graphene synthesis method that induce localized heating. Morphology, rather than thermal resistance, therefore dictates power handling limits in graphene devices.

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TYPE Journal Article YEAR 2016
DOIOSTIScopus

Oxidation of ultrathin GaSe

Applied Physics Letters

Bays, Nathan R.; Mcdonald, Anthony; Ohta, Taisuke; Howell, Stephen W.; Spataru, Dan C.; Kalugin, Nikolai G.

Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga2Se3 and amorphous Se. Furthermore, photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

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TYPE Journal Article YEAR 2015
DOIOSTI
Results 26–50 of 61
Results 26–50 of 61
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