Low Thermal Resistances at GaN–SiC Interfaces for HEMT Technology

Cho, Jungwan; Bozorg-Grayeli, Elah; Altman, David; Asheghi, Mehdi; Goodson, Kenneth E.

doi:10.1109/led.2011.2181481

Cited by 90 publications

(57 citation statements)

References 16 publications

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“…8,9 Prior studies agree that the AlN nucleation layer is a dominant thermal resistance in both LED 10 and HEMT architectures. 2,3,11,12 The source of this thermal resistance, however, is as yet experimentally unresolved as the total thermal resistance R T consists of three components: (1) the AlN/substrate TBR (TBR sub ), (2) the AlN intrinsic resistance L AlN /k AlN (where L is film thickness and k is thermal conductivity), and (3) the GaN/AlN TBR. Our prior study suggests that TBR sub is largest for AlN films grown on mechanically polished (MP) SiC substrates.…”

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confidence: 99%

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

Freedman

Leach

et al. 2013

Journal of Applied Physics

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Thickness dependent thermal conductivity measurements were made on aluminum nitride (AlN) thin films grown by two methods on the (0001) surfaces of silicon carbide (SiC) and sapphire substrates with differing surface roughness. We find that the AlN itself makes a small contribution to the overall thermal resistance. Instead, the thermal boundary resistance (TBR) of 5.1 6 2.8 m 2 K/GW between the AlN and substrate is equivalent to 240 nm of highly dislocated AlN or 1450 nm of single crystal AlN. An order-of-magnitude larger TBR was measured between AlN films and SiC substrates with increased surface roughness (1.2 nm vs. 0.2 nm RMS). Atomic resolution TEM images reveal near-interface planar defects in the AlN films grown on the rough SiC that we hypothesize are the source of increased TBR. Nitride semiconductors are essential for blue/green light emitting diodes (LEDs) and high electron mobility transistors (HEMTs). LEDs are now being pushed to high power for lighting applications causing considerable heat generation due to Joule heating and inefficiencies in light production. 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. [4][5][6][7] Internal thermal resistance of nitride devices is complicated by the presence of interfaces between films and defects within films that scatter phonons and suppress thermal conductivity below bulk values.Non-native silicon carbide (SiC) and sapphire substrates are used for the commercial growth of nitride films because gallium nitride (GaN) and aluminum nitride (AlN) substrates are not yet economically viable. Growth is initiated with an AlN nucleation layer because direct growth of GaN on these substrates is not favorable at high temperatures. Due to a mismatch in the lattice parameters (a) of AlN (a AlN ¼ 3.07 Å ) with SiC (a SiC ¼ 3.11 Å ) and sapphire (a Sapp ¼ 4.785 Å ), dislocations and surface defects form at the interface and impact the quality of subsequent growth. Though SiC and AlN have a small mismatch (1%), their high elastic moduli require stress relief through such defect formation. 8,9 Prior studies agree that the AlN nucleation layer is a dominant thermal resistance in both LED 10 and HEMT architectures. 2,3,11,12 The source of this thermal resistance, however, is as yet experimentally unresolved as the total thermal resistance R T consists of three components: (1) the AlN/substrate TBR (TBR sub ), (2) the AlN intrinsic resistance L AlN /k AlN (where L is film thickness and k is thermal conductivity), and (3) the GaN/AlN TBR. Our prior study suggests that TBR sub is largest for AlN films grown on mechanically polished (MP) SiC substrates. 5 Nonetheless, it is unclear whether this conclusion holds for SiC vs. sapphire substrates, different growth techniques, or varied su...

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confidence: 99%

“…The diffuse mismatch model predicts that the TBR of a perfect AlN-SiC interface can be as low as 0.6 m 2 K/ GW. 12 To the detriment of heat dissipation in many important technologies, the defects near the AlN-SiC interface clearly play a significant role in increasing the TBR beyond this value.…”

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confidence: 99%

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

Freedman

Leach

et al. 2013

Journal of Applied Physics

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“…Since the TBReff is temperature-dependent [7], it should be noted that the all measurements were done at an interface temperature of GaN-SiC around 160 reported TBR values for standard GaN/SiC device structures [7]. Since the crystalline quality and the thermal conductivity of an AlN layer were shown to improve considerably along with increased thickness [8,11]. An intriguing question arises: shall the thickness of an AlN NL be increased to reduce TBReff?…”

Section: B Tbreff Of the Aln Nucleation Layermentioning

confidence: 99%

“…Previously, substantial effort has been made to establish the correlation between the effective TBR (TBReff; the total thermal resistance contributed from the AlN NL and its interfacial regions) and the properties of AlN NLs through structural investigations using transmission electron microscopy (TEM) [6][7][8]. However, no detailed attention was paid to the interfacial conditions, particularly, the AlN/SiC interface, i.e.…”

Section: Introductionmentioning

confidence: 99%

Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface

Chen

Pomeroy

Rorsman

et al. 2015

Journal of Crystal Growth

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The crystalline quality of AlGaN/GaN heterostructures was improved by optimization of surface pretreatment of the SiC substrate in a hot-wall metal-organic chemical vapor deposition reactor. X-ray photoelectron spectroscopy measurements revealed that oxygenand carbon-related contaminants were still present on the SiC surface treated at 1200 o C in H2 ambience, which hinders growth of thin AlN nucleation layers with high crystalline quality.As the H2 pretreatment temperature increased to 1240 o C, the crystalline quality of the 105 nm thick AlN nucleation layers in the studied series reached an optimal value in terms of full width at half maximum of the rocking curves of the (002) and (105)

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“…The low-temperature buffer layer method allows improvements in the properties of optoelectronic devices especially for the growth of III-nitride semiconductor on a sapphire substrate [3]. However, the low thermal conductivity of the buffer layer prevents heat conduction in high-power devices [4][5][6]. To take advantage of the material properties, direct growth is preferable.…”

Section: Introductionmentioning

confidence: 99%

Selective growth of GaN on SiC substrates with femtosecond-laser-induced periodic nanostructures

Miyagawa

Okabe

Miyachi

et al. 2016

Trans. Mat. Res. Soc. Japan

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A 6H-SiC substrate with femtosecond-laser-induced periodic nanostructures was used as an underlayer for GaN growth. GaN nuclei were formed on the periodic nanostructure selectively. The in-plane direction of GaN was dependent on the in-plane direction of the SiC substrate, and no dependent on the direction of the periodic nanostructures or laser scanning. We suggest that the fine structure and high wettability at the region of the periodic nanostructure enhanced the adsorption of GaN nuclei preferentially. This technique will enable selective growth without masks or solution exposure.

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Low Thermal Resistances at GaN–SiC Interfaces for HEMT Technology

Cited by 90 publications

References 16 publications

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

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

Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface

Selective growth of GaN on SiC substrates with femtosecond-laser-induced periodic nanostructures

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