High temperature operation and failure of Ga2O3 Schottky barrier diodes: An <i>in situ</i> TEM study

The β-polymorph gallium oxide (Ga2O3) is a promising material for next generation power electronics in extreme environments due to its ultra-wide bandgap with a high theoretical breakdown electric field. However, there is a gap between their predicted and observed reliability at high temperatures or radiation. Here, we investigated the forward bias induced degradation of the β-Ga2O3 Schottky barrier diode (SBD) during high temperature operation. Instead of using conventional post-degradation characterization, we adopted in situ high temperature operation of the β-Ga2O3 SBD inside a transmission electron microscope for real time visualization of the defect nucleation and evolution leading to degradation. The degradation mechanism involves the generation of vacancy clusters and nanoscale amorphized regions by the external and self-heating driven thermal field, which induces higher compressive strain on the β-Ga2O3 crystal. The nanoscale defects created lead to dislocations and stacking fault formation, mostly along the (200) lattice planes, under high temperature biasing conditions. The ultimate breakdown of the diode involves metal pool formation through the intermixing of the Ni/Au Schottky contact metals, which diffuse into the β-Ga2O3 drift layer under high electro-thermal stress. The accumulated defects at the anode metal pool/β-Ga2O3 interface cause highly nonuniform localized strain by void formation, which led to the final breakdown of the diode. The fundamental insights into the defect nucleation and propagation leading to failure may be useful to improve the reliability of β-Ga2O3 based devices for high temperature operation.