Abstract
Through the technique of solid phase epitaxy (SPE), an epitaxial Ge 0.955 Sn 0.045 film was formed on a Ge substrate by depositing an amorphous GeSn film followed by a rapid thermal annealing at 550°C. A process that uses a SiO 2 capping layer on the amorphous GeSn film during SPE was proposed and it prevents Sn precipitation from occurring while maintaining a smooth surface due to the reduced surface mobility of Sn atoms. The high-quality epitaxial GeSn film was observed to have single crystal structure, uniform thickness and composition, and tiny surface roughness with root mean square of 0.56 nm. With a SnO x -free surface, Yb 2 O 3 -gated GeSn metal-oxide-semiconductor (MOS) capacitors with equivalent oxide thickness (EOT) of 0.55 nm were developed. A small amount of traps inside the Yb 2 O 3 was verified by negligible hysteresis in capacitance measurement. Low leakage current of 0.4 A/cm 2 at gate bias of flatband voltage (V FB )-1V suggests the high quality of the gate dielectric. In addition, the feasibility of using Yb 2 O 3 to well passivate GeSn surface was also evidenced by the small interface trap density (D it ) of 4.02 × 10 11 eV -1 cm -2 , which can be attributed to smooth GeSn surface and Yb 2 O 3 valency passivation. Both leakage current and D it performance outperform other passivation techniques at sub-nm EOT regime. The proposed epitaxial GeSn film along with Yb 2 O 3 dielectric paves an alternative way to enable high-performance GeSn MOS devices.