Barrier height enhancement in β-Ga₂O₃ Schottky diodes using an oxygen-rich ultra-thin AlO_x interfacial layer

Schottky barrier height (SBH) enhancement directly translates into increased breakdown voltage (V_BR) of β-Ga₂O₃ Schottky barrier diodes (SBDs). In this work ultra-thin (5, 10 and 15 ˚A) oxygen-rich AlO_x interfacial layers (ILs), deposited using plasma-enhanced atomic layer deposition (PEALD), are shown to enhance the SBH of post-metallization oxygen annealed Pt/AlO_x/β-Ga₂O₃ SBDs by upto 0.8 eV resulting in a maximum V_BR of nearly 500 V (2× gain) on 2-4 × 10¹⁶ cm⁻³ doped substrates, without compromising the specific on-resistance. The SBH and V_BR enhancement is observed on (¯201) as well as (001) surfaces. XPS analysis shows that excess oxygen interstitial concentration in 5 ˚A AlO_x films decreases (increases) with increasing thickness (oxygen anneal), making them more stoichiometric. The decreasing (increasing) trend in SBH and V_BR with increasing IL thickness (oxygen anneal) is consistent with the XPS-derived O/Al ratio of the films and the formation of an AlO_x/β-Ga₂O₃ interfacial dipole due to a difference in oxygen areal densities. The AlO_x deposition can be easily integrated with field management methods such as field plates and guard rings that can further enhance β-Ga₂O₃ SBD performance.