Thermal characterization of gallium oxide Schottky barrier diodes.

The higher critical electric field of ß-gallium oxide (Ga2O3) gives promise to the development of next generation power electronic devices with improved size, weight, power, and efficiency over current state-of-the-art wide bandgap devices based on 4H-silicon carbide (SiC) and gallium nitride (GaN). However, it is expected that Ga2O3 devices will encounter serious thermal issues due to the poor thermal conductivity of the material. In this work, self-heating in Ga2O3 Schottky barrier diodes under different regimes of the diode operation was investigated using diverse optical thermography techniques including thermoreflectance thermal imaging, micro-Raman thermography, and infrared thermal microscopy. 3D coupled electro-thermal modeling was used to validate experimental results and to understand the mechanism of heat generation for the diode structures. Measured top-side and cross-sectional temperature fields suggest that device and circuit engineers should account for the concentrated heat generation that occurs near the anode/Ga2O3 interface and/or the lightly doped drift layer under both forward and high voltage reverse bias conditions. Results of this study suggest that electro-thermal co-design techniques and top-side thermal management solutions are necessary to exploit the full potential of the Ga2O3 material system.

Crystalline polymer nanofibers with ultra-high strength and thermal conductivity.

Polymers are widely used in daily life, but exhibit low strength and low thermal conductivity as compared to most structural materials. In this work, we develop crystalline polymer nanofibers that exhibit a superb combination of ultra-high strength (11 GPa) and thermal conductivity, exceeding any existing soft materials. Specifically, we demonstrate unique low-dimensionality phonon physics for thermal transport in the nanofibers by measuring their thermal conductivity in a broad temperature range from 20 to 320 K, where the thermal conductivity increases with increasing temperature following an unusual ~T1 trend below 100 K and eventually peaks around 130-150 K reaching a metal-like value of 90 W m-1 K-1, and then decays as 1/T. The polymer nanofibers are purely electrically insulating and bio-compatible. Combined with their remarkable lightweight-thermal-mechanical concurrent functionality, unique applications in electronics and biology emerge.