Unique semiconducting behavior of Ultra-Thin Nickel Silicide Films

Nickel silicide (NiSi) has been extensively utilized in the photovoltaics mainly as adhesion promoter and as ohmic contact in silicide-on-Si Schottky-junction SCs.¹ However, its lack of bandgap has restricted its applications in FETs, optoelectronics, thermoelectrics etc. ^2,3

Herein, we demonstrate modification of the electronic band structure of NiSi via. producing wafer scale single-crystal like ultra-thin films of < 6 nm. These films demonstrate a monolithic enhancement of room temperature Seebeck (S) value vs. rapid thermal annealing (RTA) temperature up to 52 μV/K for the film annealed at 500 °C, indicating p-type semiconducting behavior. Interestingly, transition to n-type was seen by further increasing the RTA temperature with a peak S value of -148 μV/K for the films annealed at 600 °C. This drastic change in the electronic transport properties is attributed to the altering of the electronic band structure due to quantum confinement. The electron transport properties were further studied through performing temperature dependent Hall and Seebeck measurements, and correlated to the structural information obtained by transition electron microscopy and X-ray crystallography. Our obtained results offer a new paradigm for the NiSi applications in the modern solid-state devices.