The effect of germanium fraction on high-field band-to-band tunneling in p⁺-SiGe/n⁺-SiGe junctions in forward and reverse biases

The dependence of band-to-band tunneling in p⁺-Si _1-xGe_x/n⁺-Si_1-xGe_x homojunctions on Ge fraction and electric field is investigated in the range 2-3×10⁸V/m. Negative differential resistance (NDR) in forward bias is observed for each device with the highest peak tunneling-current density of 8.2 kA/cm² without any postannealing step. Reverse-biased band-to-band tunneling, as relevant for tunneling field-effect transistors, is also measured. Tunneling via junction defects can mask band-to-band tunneling and the observation of NDR at forward bias confirms negligible tunneling via those defects. Both forward-biased and reverse-biased data are compared with models versus electric field and Ge fraction.