Ultra-Wide band Gap Semiconductor Materials


Wide bandgap (WBG) SiC and GaN high-power and RF electronics are maturing rapidly, and significant future market growth is expected. To satisfy the market for civilian and military applications, greater efficiency with reduced size, weight, and power (SWaP) is indispensable. Ultrawide-bandgap (UWBG) materials, wide bandgaps significantly wider that the 3.4 eV of GaN, will represent a challenging new area of research in semiconductor materials, physics, devices, and applications.

UWBG materials include AlGaN/AlN, Ga2O3, diamond, and perhaps others not yet discovered. Because many of the figures-of-merit for device performance scale with increasing bandgap in a highly non-linear manner, these UWBG materials have the potential for far superior performance than WBG materials have. In other words, moving from GaN to AlN gives an increase in bandgap by a factor of 6.0 eV/3.4 eV ≈ 1.8, but a nonlinear increase in the baliga figure-of-merit (BFOM) of ≈ 34 ≈ (1.8)6 since the BFOM scales approximately as the sixth power of the semiconductor bandgap.


However, the reliability in these devices are limited, in part, by the intense heating that occurs in these new devices. Smaller size and higher power means substantially higher power density, this high temperature for individual devices. Therefore, UWBG devices inevitably confront a severe thermal problem.

Even worse, Ga2O3 has poor thermal conductivity, in the range of 10-27 W/m-K at room temperature, which is one or two orders of magnitude lower than those of other UWBG semiconductors, and therefore poor heat-dissipation capability. This low thermal conductivity is perhaps the single most serious potential weakness of Ga2O3 for power electronics. This weakness, however, signifies a key research opportunity/challenge to circumvent the low thermal conductivity of Ga2O3.

Principle causes of microelectronic circuit failure
Arrhenius plot of an extrapolated lifetime of 108 h @ 175 °C


In this study, we utilize Raman Spectroscopy, Transient Thermal Imaging (TTI), and Time-domain Thermoreflectance (TDTR) to explore not only the temperature distribution in UWBG power devices, but explore thermal properties of UWBG material.

Transient Thermoreflectance Imaging (TTI) of GaN HEMT using different wavelength LED excitation sources.
Time-domain Thermoreflectance (TDTR) Set-up in Graham Group

George Woodruff School of Mechanical Engineering