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Abstract High thermal conductivity electronic materials are critical components for high-performance electronic and photonic devices as both active functional materials and thermal management materials. We report an isotropic high thermal conductivity exceeding 500 W m −1 K −1 at room temperature in high-quality wafer-scale cubic silicon carbide (3C-SiC) crystals, which is the second highest among large crystals (only surpassed by diamond). Furthermore, the corresponding 3C-SiC thin films are found to have record-high in-plane and cross-plane thermal conductivity, even higher than diamond thin films with equivalent thicknesses. Our results resolve a long-standing puzzle that the literature values of thermal conductivity for 3C-SiC are lower than the structurally more complex 6H-SiC. We show that the observed high thermal conductivity in this work arises from the high purity and high crystal quality of 3C-SiC crystals which avoids the exceptionally strong defect-phonon scatterings. Moreover, 3C-SiC is a SiC polytype which can be epitaxially grown on Si. We show that the measured 3C-SiC-Si thermal boundary conductance is among the highest for semiconductor interfaces. These findings provide insights for fundamental phonon transport mechanisms, and suggest that 3C-SiC is an excellent wide-bandgap semiconductor for applications of next-generation power electronics as both active components and substrates.
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The Doping Dependence of the Thermal Conductivity of Bulk Gallium Nitride Substrates
Abstract Gallium nitride (GaN) has emerged as one of the most attractive base materials for next-generation high-power and high-frequency electronic devices. Recent efforts have focused on realizing vertical power device structures such as in situ oxide, GaN interlayer based vertical trench metal–oxide–semiconductor field-effect transistors (OG-FETs). Unfortunately, the higher-power density of GaN electronics inevitably leads to considerable device self-heating which impacts device performance and reliability. Halide vapor-phase epitaxy (HVPE) is currently the most common approach for manufacturing commercial GaN substrates used to build vertical GaN transistors. Vertical device structures consist of GaN layers of diverse doping levels. Hence, it is of crucial importance to measure and understand how the dopant type (Si, Fe, and Mg), doping level, and crystal quality alter the thermal conductivity of HVPE-grown bulk GaN. In this work, a steady-state thermoreflectance (SSTR) technique was used to measure the thermal conductivity of HVPE-grown GaN substrates employing different doping schemes and levels. Structural and electrical characterization methods including X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS), Raman spectroscopy, and Hall-effect measurements were used to determine and compare the GaN crystal quality, dislocation density, doping level, and carrier concentration. Using this comprehensive suite of characterization methods, the interrelation among structural/electrical parameters and the thermal conductivity of bulk GaN substrates was investigated. While doping is evidenced to reduce the GaN thermal conductivity, the highest thermal conductivity (201 W/mK) is observed in a heavily Si-doped (1–5.00 × 1018 cm−3) substrate with the highest crystalline quality. This suggests that phonon-dislocation scattering dominates over phonon-impurity scattering in the tested HVPE-grown bulk GaN substrates. The results provide useful information for designing thermal management solutions for vertical GaN power electronic devices.
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- Award ID(s):
- 1934482
- PAR ID:
- 10207169
- Date Published:
- Journal Name:
- Journal of Electronic Packaging
- Volume:
- 142
- Issue:
- 4
- ISSN:
- 1043-7398
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT AlN has the largest bandgap in the wurtzite III‐nitride semiconductor family, making it an ideal barrier for a thin GaN channel to achieve strong carrier confinement in field‐effect transistors, analogous to silicon‐on‐insulator technology. Unlike /Si/, AlN/GaN/AlN can be grown fully epitaxially, enabling high carrier mobilities suitable for high‐frequency applications. However, developing these heterostructures and related devices has been hindered by challenges in strain management, polarization effects, defect control, and charge trapping. Here, the AlN single‐crystal high electron mobility transistor (XHEMT) is introduced, a new nitride transistor technology designed to address these issues. The XHEMT structure features a pseudomorphic GaN channel sandwiched between AlN layers, grown on single‐crystal AlN substrates. XHEMTs demonstrate RF performance on par with the state‐of‐the‐art GaN HEMTs, achieving 5.92 W/mm output power and 65% peak power‐added efficiency at 10 GHz under 17 V drain bias. These devices overcome several limitations present in conventional GaN HEMTs, which are grown on lattice‐mismatched foreign substrates that introduce undesirable dislocations and exacerbated thermal resistance. With the recent availability of 100‐mm AlN substrates and AlN's high thermal conductivity (340 W/), XHEMTs show strong potential for next‐generation RF electronics.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1115/1.4047578
