We studied the operation of a single quantum well laser by examining t
he tested device with a scanning electron microscope (SEM) working in
differential voltage contrast (DVC) mode. A MOCVD-grown structure cons
ists of 60 Angstrom of In0.2Ga0.8As, positioned between layers of GaAs
, each 100 Angstrom thick. The specially cleaved laser structure was f
orward biased to get through the inverse population, threshold, and st
imulated emission mode. In various modes of operation of the laser, th
e in situ DVC profiling of the quasi-Fermi energy across the device wa
s performed. The intensity of the laser emission was simultaneously me
asured by a detector positioned in the SEM chamber. Starting with an e
quilibrium energy diagrams of an unbiased laser, we reconstructed the
complete nonequilibrium energy diagrams from the experimental profile
of quasi-Fermi levels. (C) 1998 Academic Press Limited.