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+-Si1−xGex /n+-Si1−xGex homojunctions on Ge fraction and electric field is investigated in the range 2–3×108 V/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.