The effect of internal fields on tunneling current in strained GaN/AlxGa1-xN(0001) structures

The influence of internal fields on tunnelling current in w-GaN/Al_xGa_1-xN(0001 ) nitride structures with strained barrier layers is investigated by the pseudopotential and scattering-matrix methods. It is shown that, for symmetric two-barrier structures, spontaneous polarization and a piezoelectric field lead to asymmetry of the current-voltage characteristic when the direction of an external field is varied. Moreover, for asymmetric structures these phenomena cause the current to depend on the position of layers along the polar axis. In confined superlattices, internal fields form a Stark ladder of electron states, which manifests itself in current peaks for a relatively weak external field (∼10 kV/cm). Pronounced features in the tunnel current are observed for layer thicknesses which are smaller in comparison with the GaAs/AlGaAs(001) structures by a factor of approximately 2. The dependence of tunnel current on the thickness and position of the layers, temperature, and degree of doping are explained from an analysis of the Stark effect for resonance states.