Jungwan Cho

Strained transition layers, which are common for heteroepitaxial growth of functional semiconductors on foreign substrates, include high defect densities that impair heat conduction. Here, we measure the thermal resistances of AlN transition layers for GaN on Si and SiC substrates in the temperature range $300<T<550$ K using time-domain thermoreflectance. We propose a model for the effective resistance of such transition films, which accounts for the coupled effects of phonon scattering on

High-power operation of AlGaN/GaN high-electron-mobility transistors (HEMTs) requires efficient heat removal through the substrate. GaN composite substrates, including the high-thermal-conductivity diamond, are promising, but high thermal resistances at the interfaces between the GaN and diamond can offset the benefit of a diamond substrate. We report on measurements of thermal resistances at GaN-diamond interfaces for two generations (first and second) of GaN-on-diamond substrates, using a comb

The temperature rise in AlGaN/GaN high-electron-mobility transistors depends strongly on the GaN-substrate thermal interface resistance (TIR). We apply picosecond time-domain thermoreflectance measurements to GaN-SiC composite substrates with varying GaN thickness to extract both the TIR and the intrinsic GaN thermal conductivity at room temperature. Two complementary data extraction methodologies yield 4-5 for the GaN-SiC TIR and 157-182 for the GaN conductivity. The GaN-SiC interface resistanc

The integration of strongly contrasting materials can enable performance benefits for semiconductor devices. One example is composite substrates of gallium nitride (GaN) and diamond, which promise dramatically improved conduction cooling of high-power GaN transistors. Here, we examine phonon conduction in GaN-diamond composite substrates fabricated using a GaN epilayer transfer process through transmission electron microscopy, measurements using time-domain thermoreflectance, and semiclassical t

The thermal management challenge posed by gallium nitride (GaN) high-electron-mobility transistor (HEMT) technology has received much attention in the past decade. The peak amplification power density of these devices is limited by heat transfer at the device, substrate, package, and system levels. Thermal resistances within micrometers of the transistor junction can limit efficient heat spreading from active device regions into the substrate and can dominate the overall temperature rise. Galliu

The performance of high-power gallium nitride (GaN) high-electron-mobility transistors (HEMTs) is limited by self-heating effects. High thermal resistances within micrometers of the active device junction often dominate the junction temperature rise and fundamentally limit the device power handling capability. The use of high-thermal-conductivity diamond in close proximity to the transistor junction can mitigate this thermal constraint, but careful attention is required to the quality of the the

High-power operation of AlGaN/GaN high-electron-mobility transistors (HEMTs) requires efficient heat removal through the substrate. GaN composite substrates including high-thermal-conductivity diamond are promising, but high thermal resistances at the interfaces between the GaN and diamond can offset the benefit of a diamond substrate. We report on measurements of the thermal resistances at the GaN-diamond interfaces for two generations (1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmln

We report the temperature dependent thermal properties of two types of GaN composite substrates (GaN-SiC and GaN-Si) using picosecond time-domain thermoreflectance (TDTR). The intrinsic thermal conductivity of the GaN buffer film decreases with increasing temperature, while the GaN-substrate thermal interface resistance (TIR) increases with increasing temperature. The strong temperature dependence of the GaN-substrate TIR suggests that microstructural defects within the AlN transition film and n

Self-heating effects severely limit the performance of high-power gallium nitride (GaN) high-electron-mobility transistors (HEMTs). High thermal resistances within micrometers of the transistor junction often dominate the junction temperature rise and fundamentally restrict the device power handling capability. The use of high-thermal-conductivity diamond near the junction can address this thermal limitation, but this approach requires careful attention to the quality of the thermal interface be