Evidence for the electron trap state associated with N-rich clusters in InGaAsN/GaAsquantum wells

Abstract

An electron trap state has been found to appear in InGaAsN/GaAs quantum wells (QWs)as a result of composition fluctuation. Evidence of composition fluctuation is shown byphotoluminescence spectra which display an additional low-energy emission due to localregions of N-rich clusters. Enhancing composition fluctuation leads to undulatedInGaAsN/GaAs interface with dot-like islands. The capacitance–voltage profiling shows anadditional peak following the QW electron ground state peak, suggesting thepresence of an electron trap state below the QW electron ground state. The emissionproperties of this trap state are similar to those of quantum dots immersed in a well.Enhancing composition fluctuation can cause an energy downward shift and spectralbroadening of this electron trap state, suggesting an increase in island size andfluctuations of the size and composition. Thus, it is deduced that the electron trap stateoriginated from the N-rich clusters in the well behaving like quantum dots. Uponmodulation, the electrons are thermally activated from this trap state to the QWelectron ground state and subsequently emitted to the GaAs bottom electrode.