Degradation of β-Ga2O3 Vertical Ni/Au Schottky Diodes Under Forward Bias

Here we report on the degradation processes of Au/Ni/
$\beta $
-Ga{2}O{3} Schottky diodes under forward bias stress which is related to their on-state reliability. In some diodes, we find a bias regime of electrical degradation occurring at a lower bias than those causing contact changes visible in optical microscopy. In this regime, the
$\text{V}_{\text {bi}}$
increases but is associated with decreasing
$\text{I}_{\text {s}}$
. In the higher-bias regime associated with contact roughing and change in appearance caused by the metallurgical changes mentioned, the
$\text{V}_{\text {bi}}$
continually increases with increased
$\text{I}_{\text {s}}$
, ideality factor, and
$\text{R}_{\text {on}}$
. In regions near the failure point, the Ni adhesion layer actually diffuses through the Au layer, which recrystallizes, and forms NiO on the top surface. This work highlights the importance of developing more thermodynamically stable refractory contacts to
$\beta $
-Ga2O3 to enhance long-term reliability.