I. Introduction
-gallium oxide (-Ga2O3) is an emerging candidate for next generation power devices largely due to its wide bandgap ( eV) property [1]. The Baliga figure of merit (BFOM) calculated based on its high breakdown field ( MV/cm) is more than three times greater than the conventional wide bandgap materials like GaN and SiC [2]. In addition, the melt-growth technique for Ga2O3 promises a cost-effective future for its bulk device platform [3], [4]. In the past few years, attempts have succeeded in fabricating Schottky barrier diodes (SBDs) on -Ga2O3 [5]–[8]. Nevertheless, the interface states that exist at the Schottky contact junction are degrading the Ga2O3 diode performance mainly due to its wide bandgap and oxygen vacancies near the surface [9]–[11]. Mechanisms such as image-force lowering (IFL) and Fermi-level pinning are studied but few explored potential solutions to improve the surface condition [12]–[16]. Surface treatments like chemical pretreatment and intentional oxidization of anode metal during sputtering deposition were reported [16], [17]. An interfacial layer between metal and semiconductor is proved to yield useful effects on Schottky-type devices [18]. Atomic layer deposited (ALD) Al2O3 is widely applied in Ga2O3-based devices owing to its relatively high-dielectric constant, large bandgap, and conformal coverage [19]. However, the insertion of an ALD Al2O3 layer will reduce the on-current and thus compromise the device performance for practical application [20]. On the other hand, reports show that ALD Al2O3 tends to have negative interface states which will cause degradation to the Schottky junction, resulting in a worsen ideality factor and subthreshold swing (SS) [21]–[23].