ABSORPTION MODULATION INDUCED BY ELECTRON-BEAM EXCITATION OF STRAINEDIN0.2GA0.8AS GAAS MULTIPLE-QUANTUM WELLS/

The effects of excess carrier generation on excitonic absorption pheno mena in nipi-doped In0.2Ga0.8As/GaAs multiple quantum wells (MQWs) was examined using a novel technique called electron beam-induced absorpt ion modulation imaging. The nipi-doping induced barrier height is dete rmined by measuring the frequency response of the absorption modulatio n as a function of temperature and employing a model which is based on thermal excitation of carriers in the limit of Boltzmann statistics. Spatial steps in the absorption modulation which correlate with the po sitions and orientation of dark line defects imaged in cathodoluminesc ence are observed. These results indicate the existence of defects in the MQWs which impede the ambipolar diffusive transport of the spatial ly separated electron-hole plasma.