High-performance Ge/GaAs heterojunction tunneling FET with a channel engineering for sub-0.5V operation

Abstract

A Ge/GaAs heterojunction provides momentous improvements in current characteristics due to its band arrangement and enhanced band-to-band tunneling. Ge has a narrow bandgap (0.67 eV) and a smaller electron affinity (4.0 eV) and GaAs has a relatively larger energy bandgap (1.42 eV) and electron affinity (4.07 eV) at room temperature. For the heterojunction of GaAs and Ge, by grafting p(+) Ge source and n(+) GaAs well in forming a GaAs-on-Ge structure, prominently high performances including current drivability of I-on = 482.6 mu A mu m(-1), current ratio (I-on/I-off) = 1.76 x 10(9), and S = 8.02 mV dec(-1) have been achieved by design optimization of doping profile aiming at extremely low drain voltage (V-DS) of 0.3 V. The design variables were VDS, the length of n(+) doped well in the GaAs layer (L-well) and n-type doping concentration in the drain junction (N-drain). Themy are confirmed by the results that Ge/GaAs heterojunction TFET is very suitable for low-power and high-speed applications.