Characterization of nonradiative recombination centers in proton-irradiated InAs/GaAs quantum dots by two-wavelength-excited photoluminescence

Nonradiative recombination (NRR) centers in as-grown and proton-irradiated InAs/GaAs quantum dot (QD) structures have been studied by two-wavelength-excited photoluminescence (PL). The PL intensity quenching of GaAs and QD emissions due to the addition of a below-gap excitation light of 0.80 eV energy indicates the presence of defect levels acting as NRR centers. The method enables us to discuss the distribution of NRR centers in GaAs and/or InAs QD regions by selecting either conduction band excitation (2.33 eV) or intermediate band excitation (1.27 eV). We have found that the densities of NRR centers in GaAs layers and the effect of quenching on GaAs emissions increase monotonically with increasing proton irradiation fluence. The QD emission intensity, however, increases at a moderate fluence of 7 × 1011 protons/cm2 owing to the defect-assisted trapping of electrons into QDs. Further incorporation of NRR centers after 4 × 1012 protons/cm2 fluence quenches the QD-PL intensity below that of an unirradiated sample.