Enhancing Ohmic Contacts in β-Ga₂O₃ via N₂ Plasma Treatment

β-Ga₂O₃ has emerged as a highly promising material for next-generation power semiconductors due to its exceptional properties such as high theoretical breakdown field and Baliga's figure-of-merit. However, the performance of β-Ga₂O₃-based devices, including SBDs and MOSFETs, is often hindered by the presence of high contact resistance between the Ga₂O₃ and metal contacts. This resistance limits device efficiency by increasing switching and conduction losses.
Conventional methods for reducing contact resistance include: 1) rapid thermal annealing (RTA) to enhance interface defects between metal and semiconductor, and 2) ion implantation to increase doping concentration beneath metal contacts. However, post-metallization annealing (400–500°C) may lead to interfacial degradation, potentially restricting the front-end-of-line process for Ga₂O₃. Moreover, ion implantation for doping can cause damage to the semiconductor lattice.
In this study, a novel annealing-free N₂ plasma treatment for achieving Ohmic contacts was demonstrated. This simple treatment successfully reduced the contact resistance to 13.1 kΩμm through a defect-compensating effect. X-ray photoelectron spectroscopy (XPS) was employed to verify the impact of N₂ plasma treatment on Ga₂O₃ bonds, while Raman spectroscopy assessed the crystalline quality of the plasma-treated region. β-Ga₂O₃ nanosheet FETs treated with N₂ plasma exhibited an impressive on/off ratio of ~10¹⁰ and a field-effect mobility of 103.7 cm²/Vs. To validate the air-stability of the N₂ plasma-treated devices, electrical measurements were conducted seven days after fabrication. This work presents a robust method to reduce contact resistance using a simple process, pushing the boundaries of β-Ga₂O₃ device performance.

This research was financially supported by the Korea Research Institute for Defense Technology Planning and Advancement (KRIT) grant funded by the Defense Acquisition Program Administration (DAPA) (KRIT-CT-22-046)