Effects of strain-induced defects on excess carrier lifetime and ambipolar diffusion in nipi-doped In_0.2Ga_0.8As/GaAs MQWs

The effects of strain-induced defects on excess carrier lifetime and transport in a nipi-doped In_0.2Ga_0.8As/GaAs multiple quantum well (MQW) structure were examined with a new method called electron beam-induced absorption modulation (EBIA) in which the kinetics of carrier transport and recombination are examined with a high-spatial, -spectral and -temporal resolution. The excess carrier lifetime and ambipolar diffusion were found to be reduced by factors of approx.10¹³ and approx.10³ compared to theoretical values, respectively, and this is attributed to the presence of strain-induced defects. The MQW excitonic absorption coefficient sensitively depends on the carrier density in the QWs, as a result of screening of the electron-hole (e-h) Coulombic interaction. Likewise, ambipolar diffusion is found to depend on the excess carrier density in a nonlinear fashion, as a result of the e-h plasma-induced changes in the local depletion widths in the vicinity of structural defects.