Fabrication and electrical characterization of Au/molecule/GaAs devices

Metal/molecule/semiconductor (MMS) heterostructures were studied in a Au/molecule/GaAs configuration. Stable monolayers of alkanemonothiols, alkanedithiols and aromaticdithiols were self-assembled on heavily doped p-type (p⁺) GaAs. FTIR spectroscopy and ellipsometry indicate the formation of uniform and reasonably thick crystalline monolayers. A low-energy indirect path technique was used to evaporate Au on the molecular layer without damaging or penetrating it. Current voltage (I-V) measurements on the Au/molecule/GaAs devices indicate a substantial increase in conductivity due to the presence of the molecular layer. The results are consistent with the presence of molecular dipole moments at the interface and seem to indicate strong molecular coupling to the contacts with a significant density of states (DOS) near the Fermi level (E_fm). Variable temperature I-V measurements exhibit very little temperature dependence in the MMS devices implying that transport through the molecular layer is tunneling-based.