We have fabricated light-emitting-diode heterostructure devices, in which a
layer of InAs self-assembled quantum dots is embedded, with an active area
of submicron size. In the electroluminescence spectra of these devices, we
observed isolated narrow peaks due to emission from individual dots. From
the shift of the peaks in an electric field (the quantum confined Stark eff
ect), we show that the ground and excited states in the dots have different
spatial alignments of the electron and hole. (C) 2000 American Institute o
f Physics. [S0003-6951(00)02526-2].