Investigation of Channel Doping Concentration and Reverse Boron Penetration on P-Type Pi-Gate Poly-Si Junctionless Accumulation Mode FETs

In this paper, the influence of channel doping concentration and reverse boron penetration on p-type Pi-gate (PG) poly-Si junctionless accumulation mode (JAM) FETs has been experimentally investigated and discussed. Effective carrier concentration (N_eff) and threshold voltage (V_TH) are found to be sensitive to doping concentration. Moreover, the positive shift in V_TH and the degradation in the subthreshold behavior for PG JAM FETs are observed after an additional source/drain (S/D) activation process. Using a low thermal-budget S/D activation process, PG JAM FETs with a suitable channel doping concentration can show excellent electrical characteristics: 1) steep subthreshold swing of 86 mV/dec.; 2) low average subthreshold swing (A.S.S.) of 96 mV/dec.; and 3) high ON/OFF current ratio (I_ON/I_OFF) of 7.7 × 10⁷ (I_ON at V_G - V_TH = -2 V and V_D = -1 V).