Abstract
Processes for Fermi level (FL) depinning on metal/n-GeSn (the doping concentration of 10 19 cm -30 with 4.5% Sn content) contact were investigated by plasma treatment on GeSn surface. Among CF 4 , NH 3 , and O 2 plasma, O 2 plasma treatment on GeSn surface prior to metal deposition is the most viable avenue to mitigate FL pinning in terms of ohmic-like behavior with improved reverse-biased current by a factor of 14 300 as compared with the untreated samples, a low contact resistance (R C ) of 3 × 10 -7 Ω-cm 2 , and the Schottky barrier height (Φ BN ) of 0.12 eV for Al/n-GeSn, and it is primarily due to the formation of GeSnO x , which possesses the desirable bandgap (E G ), conduction band offset (ΔE c ), and permittivity (κ) value with the capability to passivate the surface dangling bonds and consequently decreases the number of surface states. R C and Φ BN compare favorably with other schemes for FL depinning for Ge technology. Furthermore, the effectiveness of FL depinning is also evidenced by the S factor as high as 0.58. Besides the promising electrical properties, this plasma-based process can tolerate larger process variation and, therefore, a larger process window due to self-limiting thickness of the GeSnO x . By combining these advantages, surface treatment by O 2 plasma paves the promising path for emerging GeSn technology.