Germanium n+/p Diodes: A Dilemma Between Shallow Junction Formation and Reverse Leakage Current Control

This paper shows that germanium n(+)/p shallow junction formation often results in poor leakage current control. It is due to the counteraction between the fast diffusion of phosphorus and the high-temperature annealing requirement for dopant activation and defect annihilation. When the dopant concentration is above a threshold value, the concentration-dependent diffusion enhances phosphorus diffusion and results in a box profile, leading to an electrical concentration lower than its solid solubility limit. A refrained thermal budget may increase the active concentration, but it is not sufficient to repair the implantation-damaged lattice. Moreover, any plasma-involved fabrication processes after rapid thermal annealing may introduce additional field-assisted defects into the depletion region when the junction is near the surface. Thus, several tradeoffs must be considered between high P activation, low junction leakage, and a shallow junction in order to obtain functional negative-channel metal-insulator-semiconductor field-effect transistors.