Thermoreflectance Temperature Mapping of Ga2O3 Schottky Barrier Diodes

Abstract

There is increasing adoption of SiC and GaN for various high-power applications, including in the areas of transportation, electricity production and distribution, control of industrial machinery, and military systems. These applications are expanding the market for wide bandgap materials beyond the existing important uses in chargers for smartphones, laptops, and television sets. The primary attraction of wide bandgap semiconductors is their ability to deliver higher power density and better efficiency as compared to equivalent devices made with silicon. Wide bandgap materials, such as SiC, GaN, and Ga2O3 can also withstand much higher temperatures, thus reducing the need for costly cooling systems. A major drawback of Ga2O3 as compared to other candidate semiconductors is its low thermal conductivity. This apparent limitation could potentially be mitigated by transferring devices to other substrates as has already been demonstrated for GaN, and/or by using heat spreaders and even top-side heat extraction. At present, the electrical performance of Ga2O3 rectifiers is limited by the presence of defects and by lower than desired breakdown voltage initiated in the depletion region near the electrode corners. In the more established SiC and GaN rectifier technologies, these shortcomings are mitigated by the use of edge termination methods whose effect is to smooth out the electric field distribution around the rectifying contact periphery. Such methods have included field plates and ion-implanted high-resistivity layers. But the recent success in producing Ga2O3 bulk wafers as well as doped epitaxial layers grown on these wafers are promising developments for power device applications of Ga2O3, especially vertical geometry rectifiers. So, if continued efforts can be successful in minimizing the on-state resistance Ron while increasing the breakdown voltage, Ga2O3-based devices can extend power switching to voltages above those possible with SiC and GaN. The thermal behavior of such devices is not only an important gage of electrical performance, but can also serve as an early indicator of the onset of failure, both spatially and temporally. Therefore, in this work, we set out to report on the thermal performance of edge-terminated, vertical geometry, Schottky diode devices. By using thermoreflectance-based thermography, we were able to map the temperature distribution on the surface of a diode with deep submicron resolutions. We also pulse activated the diodes with various prescribed periods and duty cycles, and tracked their thermal response by capturing the surface temperature fields at different times within each activation period. In doing so, we were able to resolve the thermal rise and decay of the active diodes. The attached figure shows an example of the temperature map obtained on the surface of a 100-µm Ga2O3 Schottky diode. The device under test is shown on the left side of the image while on the right side, the temperature rise field is shown just before the device is turned off. The line plot on the bottom left side shows the average temperature in the center of the device at different time points within the 5-second period that the shown device was pulsed at. Figure 1