Modifying the Barrier Height of β-Ga₂O₃ Schottky Contacts Using Covalently Grafted Organic Layers

Beta gallium oxide (β-Ga 2 O 3 ) is a transparent semiconductor that is attracting significant interest as researchers attempt to harness its ultrawide bandgap (∼4.8 eV at 300 K) and high breakdown strength (∼8 MV/cm) for applications in high-efficiency power electronics, deep ultraviolet sensing, and transparent electronics. We have recently shown (Carroll et al., ACS Appl. Electron. Mater. 2021, 3, 5608–5620) that the covalent modification of β-Ga 2 O 3 surfaces with organic layers, in particular, aryl and phosphonic acid molecules, can produce significant changes in near-surface band bending and electron density. However, it is not known whether these changes will persist during electronic device fabrication and influence the performance of the resulting devices. In this work, we compare the barrier heights of Pd Schottky contacts (SCs) fabricated on the (001), (010), and ( 2 ¯ 01 ) surfaces of β-Ga 2 O 3 following the electrografting of 4-nitrophenyl (NP) layers and the spontaneous grafting of octadecylphosphonic acid (ODPA) molecules. We show that NP modification consistently produces significant increases in the barrier height of Pd:β-Ga 2 O 3 SCs of between 0.3 and 0.8 eV on each of the commonly used crystallographic surfaces of β-Ga 2 O 3 . In contrast, only a small decrease in barrier height of ∼0.1 eV on the (001) β-Ga 2 O 3 surface was observed following ODPA modification, which may be due to the much thinner nature of the ODPA layers compared to those produced by NP modification. However, we have conclusively shown that the surface modification of β-Ga 2 O 3 with electrografted NP layers is a viable strategy for significantly increasing the barrier height of β-Ga 2 O 3 SCs, a finding that may have significant consequences for the fabrication of high-performance β-Ga 2 O 3 electronic devices.