Germanium nMOSFETs With Recessed Channel and S/D: Contact, Scalability, Interface, and Drain Current Exceeding 1 A/mm

A novel recessed channel and source/drain (S/D) technique is employed in Ge nMOSFETs, which greatly improves metal contacts to n-type Ge with contact resistance of down to 0.23 Ω · mm and enhances gate electrostatic control with ION/IOFF of 10⁵. The recessed S/D contacts are thoroughly investigated, showing strong dependence on the doping profile. For the first time, the drain current of Ge nMOSFETs has exceeded 1 A/mm with an Id of 1043 mA/mm on a 40-nm Lch device. Scalability study is carried out in deep sub-100-nm region on Ge nMOSFETs with L_ch down to 25 nm. Interface study is also conducted with a new postoxidation method introduced, which significantly reduces the interface trap density. Device behaviors corresponding to interface traps are also investigated through a Technology Computer Aided Design simulation.