Reducing Thermal Resistance of AlGaN/GaN Electronic Devices Using Novel Nucleation Layers

Abstract

Currently, up to 50% of the channel temperature in AlGaN/GaN electronic devices is due to the thermal-boundary resistance (TBR) associated with the nucleation layer (NL) needed between GaN and SiC substrates for high-quality heteroepitaxy. Using 3-D time-resolved Raman thermography, it is shown that modifying the NL used for GaN on SiC epitaxy from the metalorganic chemical vapor deposition (MOCVD)-grown standard AlN-NL to a hot-wall MOCVD-grown AlN-NL reduces NL TBR by 25%, resulting in ∼10% reduction of the operating temperature of AlGaN/GaN HEMTs. Considering the exponential relationship between device lifetime and temperature, lower TBR NLs open new opportunities for improving the reliability of AlGaN/ GaN devices.

Layer-by-layer thermal conductivities of the Group III nitride films in blue/green light emitting diodes

“…Figure 3(a) shows a two order of magnitude reduction in our measured thermal conductivity relative to that of bulk single crystal AlN measured by Slack. 4 Values of similar magnitude (1 W/mK at 300 K) in AlN films were measured by Dinescu et al 6 and Riedel et al 8 Dinescu et al 6 also observed temperature invariant thermal conductivity from 77 to 300 K (reproduced in Figure 3(a)). Plan view TEM images, shown in Figure 3(b), reveal that the AlN layer has an extremely high threading dislocation density, an effect attributed to its lattice mismatch with the SiC substrate.…”

“…[3][4][5][6] Previous thin film studies have been (i) based on ideal films with low defect concentrations that are unrepresentative of LED grade films 3,7 or (ii) focused on high electron mobility transistors (HEMTs), rather than LED architectures. [8][9][10] Neither submicron GaN films nor real nitride based LED devices have been investigated.Studies of Si and other thin films have demonstrated that thermal conductivity is greatly reduced when the thickness of the film or the defect spacing is less than the intrinsic mean free path of the phonons. 5,11,12 Nitride based LED structures are fabricated from multiple layers of thin films ranging from 3 nm to 100 nm in thickness; whereas, the spectrum-average phonon mean free path in GaN at 300 K is $100 nm, 13 and the longest phonon mean free paths in the spectrum are much greater.…”

“…[3][4][5][6] Previous thin film studies have been (i) based on ideal films with low defect concentrations that are unrepresentative of LED grade films 3,7 or (ii) focused on high electron mobility transistors (HEMTs), rather than LED architectures. [8][9][10] Neither submicron GaN films nor real nitride based LED devices have been investigated.…”

“…The MQW layer exhibited an even further reduced thermal conductivity compared to the InGaN layer. It is likely that interfaces within the repeated MQW units ((GaN) 8 The AlN buffer layer was found to have the smallest thermal conductivity of all the individual layers of interest. Figure 3(a) shows a two order of magnitude reduction in our measured thermal conductivity relative to that of bulk single crystal AlN measured by Slack.…”

The impact of film thickness and substrate surface roughness on the thermal resistance of aluminum nitride nucleation layers

“…1 HEMTs are essential to high-power and high-speed switching operations that generate heat as a byproduct. 2,3 While thermal packaging is essential to minimize operating temperatures, nearly half of the total thermal resistance comes from the nitride device itself. 2,3 Experiments on bulk nitrides show that thermal transport is phonon-dominated.…”