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

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 μA μm^-1, current ratio (I_on/I_off)=1.76×10⁹, 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 V_DS, the length of n⁺ doped well in the GaAs layer (L_well) and n-type doping concentration in the drain junction (N_drain). They are confirmed by the results that Ge/GaAs heterojunction TFET is very suitable for low-power and high-speed applications.