Effect of Chemical Bond Type on Electron Transport in GaAs−Chemical Bond−Alkyl/Hg Junctions

How alkyl chain molecules are bound chemically to GaAs directly affects current transport through GaAs/Alkyl/Hg junctions. We used two different binding groups, thiols that form an As−S bond and phosphonates with the much stronger Ga−O (actually Ga−O−P) bond. Analyzing transport through the junctions as tunneling through a dielectric medium of defined thickness, characterized by one barrier and the effective mass of the electronic carrier, we find the main difference in the electronic properties between the two systems to be the effective mass, 1.5−1.6 m_e with thiols and 0.3 m_e with phosphonates. The latter value is similar to that found with, or predicted for, other systems. We ascribe this difference primarily to less scattering of carriers by the Ga−O than by the As−S interface.