β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor (E G ∼ 4.8 eV), which promises generational improvements in the performance and manufacturing cost over today’s commercial wide bandgap power electronics based on GaN and SiC. However, overheating has been identified as a major bottleneck to the performance and commercialization of Ga2O3 device technologies. In this work, a novel Ga2O3/4H-SiC composite wafer with high heat transfer performance and an epi-ready surface finish has been developed using a fusion-bonding method. By taking advantage of low-temperature metalorganic vapor phase epitaxy, a Ga2O3 epitaxial layer was successfully grown on the composite wafer while maintaining the structural integrity of the composite wafer without causing interface damage. An atomically smooth homoepitaxial film with a room-temperature Hall mobility of ∼94 cm2/Vs and a volume charge of ∼3 × 1017 cm–3 was achieved at a growth temperature of 600 °C. Phonon transport across the Ga2O3/4H-SiC interface has been studied using frequency-domain thermoreflectance and a differential steady-state thermoreflectance approach. Scanning transmission electron microscopy analysis suggests that phonon transport across the Ga2O3/4H-SiC interface is dominated by the thickness of the SiN x bonding layer and an unintentionally formed SiO x interlayer. Extrinsic effects that impact the thermal conductivity of the 6.5 μm thick Ga2O3 layer were studied via time-domain thermoreflectance. Thermal simulation was performed to estimate the improvement of the thermal performance of a hypothetical single-finger Ga2O3 metal–semiconductor field-effect transistor fabricated on the composite substrate. This novel power transistor topology resulted in a ∼4.3× reduction in the junction-to-package device thermal resistance. Furthermore, an even more pronounced cooling effect is demonstrated when the composite wafer is implemented into the device design of practical multifinger devices. These innovations in device-level thermal management give promise to the full exploitation of the promising benefits of the UWBG material, which will lead to significant improvements in the power density and efficiency of power electronics over current state-of-the-art commercial devices.

No abstract

Silicon carbide (SiC) is a promising material for high-power and high-frequency electronics due to its wide band gap, large breakdown field, and high thermal conductivity. Several applications of micro- and nanoelectronics are found in aqueous environments; thus, it is important to understand the atomic-scale interactions between SiC and water, as these interactions govern the transport processes at solid–liquid interfaces. In an effort to characterize the solid–liquid interactions, the wetting behavior of 3C-SiC was numerically investigated. The wettability of two crystallographic planes ((100) and (111)) was characterized, allowing to have silicon or carbon terminations. It was found that the crystallographic planes as well as the atomic surface terminations play an important role in the wetting behavior of 3C-SiC. Higher hydrophilicity was observed for the Si-terminated surfaces as well as for the SiC(111) crystallographic plane. A combination of a mean-field model of wettability and an analysis of the interfacial liquid structuring led to explain the wetting behavior of the different crystallographic planes (silicon- or carbon-terminated). These numerical and theoretical findings underscore the importance of proper modeling strategies when using wetting behavior as the framework for the modeling of interfaces.

Thermal transport across interfaces made of 3C-type silicon carbide (SiC) and water was investigated by means of nonequilibrium classical molecular dynamics. The effects of different crystallographic planes and atomic surface terminations were studied, as it pertains to interfacial heat transfer. Hydrophilic and hydrophobic conditions were analyzed by modifying the interfacial bonding strength between the solid and liquid phases. The formation of structures in the liquid molecules close to the solid substrate was observed and found that such structures are sensitive to the uppermost atomic layer termination, the wettability condition, and the temperature of the system. It was found that the interfacial heat transfer and the wetting properties are not universally related and to obtain a more comprehensive description, it is required to include the structuring observed in the liquid phase at the interface. A reconciliation of the thermal boundary conductance calculations was found after the density depletion length was utilized as the descripting parameter.

In this investigation, the thermal transport across graphite−water interfaces was studied by means of nonequilibrium classical molecular dynamics (NEMD) simulations. The main focus of this work was the assessment of the interface modeling approach of the nonbonded interactions, where empirical models optimized for predicting an experimental wetting condition were compared against interface models derived from multibody electronic structure methods. To understand the mechanisms involved in the interfacial heat transfer, spectral heat flux mapping and phonon dynamics (spectral energy density) analyses were implemented to query the vibrational composition of interfacial heat transfer. Aside from the NEMD formulation, a modified acoustic mismatch model including interfacial interactions was utilized. The results obtained from this investigation are twofold. (i) The minimum of the adsorption energy curve (binding energy) can be used to fully describe the wetting response of an atomically dense surface, such as graphene/graphite, as irrespective of the interface modeling approach, a linear relationship exists between the work of adhesion and the binding energy. (ii) The sole effect of the solid−liquid affinity, characterized by wetting behavior, does not provide a conclusive description of the interfacial heat transfer when different interface models are used, which is consistent with recent experimental reports. Alternatively, the interfacial liquid depletion provided a sound explanation of the nonconclusive observations derived from correlating wetting behavior to thermal transport. Furthermore, the critical impact that the modeling techniques have has been brought to light in the description of heat transfer across solid−liquid interfaces. These findings call to review the modeling efforts of interfacial heat transfer when using empirical mixing rules or matching wetting behavior to model solid−liquid interfaces.