Regrown ohmic contacts to InxGa1−xAs approaching the quantum conductivity limit

We report contact resistances between source-drain regrowth and underlying semiconductor quantum well channels in test structures designed for characterization of source and drain access resistances in III-V MOSFETs. Regrowths included both N+ InAs and N+ graded InAs-In_xGa_1-xAs; channel materials included both unstrained In_0.53Ga_0.47As and unstrained InAs. The access resistivity correlates strongly with the sheet carrier concentration of the 2-dimensional electron gas, consistent with quantum- but not classical- transport theory. With source-drain regrowth of InAs contacts to InAs channels, the total access resistance is within a factor of two of the inverse of Landauer´s quantum-state-limited conductance [1-3]. The state-limited conductance in TLM structures and the ballistic MOSFET transconductance both arise from the same physical process, hence the Landauer term in the TLM resistance does not contribute to the MOSFET source access resistance. Application of TLM data to transistor characterization must therefore correct for the state-limited access resistivity. Samples with contacts regrown onto channels with high 5·10¹⁴/cm² sheet carrier concentration, hence low quantum-state-limited resistance, showed extremely low 12.7 Ω-μm access resistivity. This demonstrates the utility of MBE regrowth for source/drain formation in III-V MOS technology.