Investigation of doping in InAs/GaSb hetero-junctions for tunnel-FETs

We report on the influence of doping on the band-edge abruptness of InAs/GaSb p-n and p-i-n tunnel diodes. Understanding and fabrication of a well-defined and sharp band edge is mandatory for tunnel FET operation. InAs/GaSb nanowire junctions were selectively grown by metal organic chemical vapor deposition (MOCVD) on silicon-on-insulator (SOI) substrates using template assisted selective epitaxy (TASE) [1]. The junctions were analyzed by scanning transmission electron microscope (STEM) showing an abrupt interface. Current-voltage measurements and conductance slope (S) analysis [2] were conducted at various temperatures. We find that (S) of tunnel diodes exhibits a temperature dependence due to trapping and de-trapping of carriers at the junction and, importantly, that high doping of p-n junctions results in steeper slopes compared to p-i-n diodes. This finding suggests that electronic states from doping impurities play a minor role in S degradation. The presence of doping independent traps at the hetero-interface still results in > 60mV/dec steepness which needs continuous investigations for subthermal device operation of tunnel FETs.