Measurement of minority carrier lifetime in GaAs and GaAs 1-xP x with an intensity-modulated electron beam

A new method of measuring short minority carrier lifetimes with a Scanning Electron Microscope (SEM) is reported. Main features are high spatial resolution (3 ωm in GaAs at 30 keV energy of beam electrons) and the insensitivity to surface recombination by use of a Schottky-contact. The shortest measurable lifetime is approx. 100 ps depending on sample conditions. The minority carrier lifetime is evaluated from the phase rotation between the measured ac-EBIC and the ac-component of the intensity modulated electron beam. The diffusion length required for the analysis is measured by the collection efficiency of the Schottky-contact, similar to the method of Wu and Wittry. Application of the method is demonstrated with a GaAs sample and a GaAs _{1- x}P _x sample. EBIC micrographs (phase and amplitude) show local flucuations of lifetime and diffusion length.