Defect-assisted apparent lowering of band offsets

We present a study of the emission of electrons from a well into the conduction band of the associated barrier. The process involved is not the usual thermionic one but a defect-assisted tunneling process, occurring from the quantum states of the well to the energy levels of the conduction band of the associated barrier, and via the energy level associated with a defect located in the barrier. This tunneling process occurs because there is band bending of the conduction band associated with the charge located in the well. This mechanism results in an apparent lowering of the band offset, which is a function of the ionization energy ${\mathrm{\Delta }}_0$ associated with the defect. Evidence of this effect is obtained on a ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{Ga}}_{\mathit{y}}$ ${\mathrm{In}}_{1\mathrm{-}\mathit{y}}$As/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$As quantum well. The apparent offset lowering is measured using the admittance spectroscopy technique and is consistent with theory.