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Representative sample structures of green-emitting nitride-based LED devices (figure not drawn to scale). The five samples are as follows: (1), (1)+(2), (1)+(2)+(3), (1)+(2)+(3)+(4), and (1)+(2)+(3)+(4)+(5). The SiO2 dielectric layer was added to each sample. The 3-omega gold pattern is enlarged in the figure. The gold line between pads performs as both a heater and a thermometer to extract the film thermal conductivities.
(a) Temperature dependent data for nitride layers (except AlN) and comparison with experimental values for bulk GaN, as well as TC and Cahill-Pohl theoretical prediction. Representative error bars are shown for one point in each data series. The comparison suggests that the observed reductions in the thermal conductivity of GaN relative to bulk, result from both dislocation density and interface thermal conductance. Alloy scattering and increased interface scattering cause further reductions in the InGaN and MQW films, respectively. (b) Thermal conductivity of GaN vs. dislocation density at 300 K. The new relaxation time based on dislocation density was added to the TC model and compared with data from Mion et al. (see Ref. 24). This revised TC model was used to calculate the solid line in (a) with the measured ρD = 1.2 × 108 cm−2 of the GaN film.
(a) Temperature dependent thermal conductivity of AlN along  in comparison with single crystal AlN data from Slack (see Ref. 4), pulsed laser deposited AlN data from Dinescu (see Ref. 6), and theoretical predictions from TC and Cahill-Pohl models. (b) A plan view TEM image of the AlN layer acquired along the  zone axis. Inset is the associated diffraction pattern. The TEM image reveals a high dislocation density 4 × 1010 cm−2 that causes additional phonon scattering. Each dark dot in the image represents a dislocation in the AlN film. The solid line in (a) has been calculated using the TC model with τD based on ρD = 4 × 1010 cm−2, and shows that the observed reductions in the thermal conductivity of AlN cannot be solely explained by dislocation scattering. (c) A cross-sectional TEM image along shows increased defect density near the AlN-SiC interface (“Reprinted with permission from Z. J. Reitmeier, S. Einfeldt, R. F. Davis, X. Y. Zhang, X. L. Fang, and S. Mahajan, Acta Mater. 57, 4001 (2009). Copyright © 2009 Elsevier.”). These defects cause very low interface conductance that further reduces the effective thermal conductivity of the AlN.
Layer-by-layer effective thermal conductivity of Group III nitride LED films at 300 K.
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