Influence of defects on electron-hole plasma recombination and transport in a nipi-doped In_xGa_1-xAs/GaAs multiple-quantum well structure

The nonlinear optical and transport properties of a nipi-doped In _xGa_1-xAs/GaAs multiple-quantum well sample (x=0.23) has been studied using a novel approach called electron-beam-induced absorption modulation (EBIA). The absorption in the sample is modulated as a result of screening of the built-in electric field in the nipi structure due to excess carrier generation. The change in field causes a Stark shift of the first quantized optical transitions in QWs which are situated in the intrinsic layers. In EBIA, a scanning electron probe is used to locally generate an electron-hole plasma that is used to study the spatial distribution of defects that impede excess carrier transport and reduce the lifetime of spatially separated carriers. The Stark shift in the MQW structure is imaged with micrometer-scale resolution and is compared with cathodoluminescence imaging results which show dark line defects resulting from strain-induced misfit dislocations. Theoretical calculations using Airy functions in the transfer-matrix method with a self-consistent field approximation were used to determine the energy states, wave functions, and carrier recombination lifetimes of the MQW as a function of the built-in field. A quantitative phenomenological analysis is employed to determine the built-in field, excess carrier lifetime, and ambipolar diffusion coefficient as a function of the excitation density. The defects are found to create potential barriers and recombination centers which impede transport and markedly reduce the excess carrier lifetime.