Structural breakdown in electrically stressed diodes

High power electronic devices based on gallium nitride are used for switching in radars, airplanes, and satellite communications where reliable operation is vital. Conventional GaN semiconductor devices can have lattice mismatch and differences in thermal conductivity, leading to high densities of threading dislocations (TDs). These TDs affect the performance of electronic devices, but no detailed microscopic investigation of their effect on GaN p-n diodes and devices has yet been reported.

Peri et al. carried out a detailed investigation of GaN-on-GaN vertical devices that were electrically stressed to the point of breakdown. They used scanning electron microscopy and cross-sectional observation via transmission electron microscopy to examine device morphology after breakdown.

Two device types, an A-series and an L-series, were studied. Both types were made using metalorganic chemical vapor deposition to grow GaN structures on GaN substrates. The substrate surfaces were treated with UV light and ozone, followed by exposure to hydrogen fluoride and hydrogen chloride to remove contaminants. The A-series devices were further subjected to etching to remove surface layers while minimizing etch damage.

The L-series showed breakdown voltages between 200 and 750 volts, while the A-series had much higher breakdown voltages between 1070 and 1270 volts. “The lower breakdown voltages for the surface-treated devices can most likely be attributed to surface oxidation during the UV-ozone treatment,” said author Prudhvi Peri.

Microscopic investigation revealed failed devices all had micron-scale surface craters and deep cracks, as well as high TD densities near these features. Devices that had not been electrically stressed showed no dislocations, cracks or other signs of damage.

These results should help guide the design of vertical power electronics by enhancing the understanding of device reliability under high voltage stress.

Source: “Structural breakdown in high power GaN-on-GaN p-n diode devices stressed to failure,” by Prudhvi Peri, Kai Fu, Houqiang Fu, Yuji Zhao, and David J. Smith, Journal of Vacuum Science and Technology A (2020) The article can be accessed at https://doi.org/10.1116/6.0000488 .