Low-hole concentration polycrystalline germanium by CO2 laser annealing for the fabrication of an enhancement-mode nMOSFET

A p-type polycrystalline Ge (poly-Ge) film processed by UV and CO2 laser annealing reduces the hole concentration from 6 × 1018 to 2 × 1016 cm−3, accompanied by poly-grain growth. The decrease in hole concentration arises from the defect annealing using a CO2 laser, as demonstrated by the changes in the work function, that is, the valence-band maximum (VBM). The laser processes reduce the thermal budget for the fabrication of an enhancement-mode poly-Ge nMOSFET, which has a Ion/Ioff ratio of 5 × 103, a Vth of 2 V, and a subthreshold swing of 250 mV/dec., and will be potential fabrication methods for monolithic 3D integrated circuits in the future.