The conduction barrier at the interface between low temperature grown GaAs and undoped GaAs

We have examined current transport across the interface between low temperature grown (LTG) GaAs and GaAs grown at normal temperatures, both n+-doped and undoped. The two types of interface, LTG GaAsn+ GaAs and LTG GaAs/undoped GaAs, exhibit ohmic and rectifying behavior, respectively. In the ohmic case, electrons can easily tunnel from the defect hopping band of the LTG GaAs, in which the Fermi level is pinned, into the conduction band of the n+ GaAs-layer. In the second case, the interface acts like a Schottky barrier since electrons must be thermally emitted from the defect hopping band of the LTG GaAs up into the conduction band of the undoped GaAs. By fitting the temperature dependence of the current-voltage relationship using thermionic emission theory, we obtain a simple, direct measure of the Fermi level depth in the LTG GaAs.