Effect of substrate surface treatment in molecular beam epitaxy on the vertical electronic transport through the film-substrate interface

We have grown n+ -GaAs films using Sn or Ge doping on n+ -GaAs substrates by molecular beam epitaxy and studied the vertical electronic transport through the film-substrate interface. An interfacial layer with high resistance and a nonlinear I-V characteristic is observed whenever the substrates have been sputter-cleaned and annealed prior to the growth. Similar results are observed for the nonsputtered substrates with a high surface coverage of carbon. Such an interfacial layer can be eliminated in both cases by a predeposition of a Sn monolayer prior to the growth of the n+ -GaAs layers.