Direct Imaging of Minority Carrier Drift in Luminescent Materials

A technique is presented to directly image charge carrier drift and diffusion in semiconductor samples over a temperature range from 300 to 10 K. A scanning electron microscope produces electron-hole pairs at a point and an applied voltage bias causes the charge carriers to drift. Upon radiative recombination, a photon is emitted at the point of generation, which is then collected and imaged by a cooled CCD camera via an optical microscope. This technique allows for the preservation of spatial information from the carrier recombination. Current resolution is $\sim $ 0.4 $\mu $m per pixel. Results will be presented from the imaging of drift behavior in high purity epitaxial GaAs as a function of temperature. Minority carrier drift over distances in excess of 100 $\mu $m at a field of $\sim $ 80 V/mm has been directly imaged using this technique for high purity room temperature n-type GaAs samples with net doping of $\sim $ 5 x 10$^{13}$ cm$^{-3} $. The characterization of the drift tails as a function of temperature will be presented and the measured spatial homogeneity of the sample depicted. The effect of near-contact electric fields due to space charge on charge carrier injection and collection at low temperature will be presented.