Quantum confined Stark effect and permanent dipole moment of InAs-GaAs self-assembled quantum dots

New information on the electron and hole wavefunctions in InAs-GaAs self-as sembled quantum dots (SAQD) is obtained from photocurrent spectroscopy of t he quantum confined Stark effect. We show that the hole is localised toward s the top of the dot, above the electron. an alignment opposite to that pre dicted by all previous theories. By means of envelope function calculations we show that this alignment can only arise if the nominally InAs dots have a graded GaxIn1-xAs composition with I decreasing from base to apex, and a relatively flat, non-pyramidal shape. In the light of these results most i f not all previous modelling of the electronic structure of InAs SAQD needs to be re-examined. The mechanisms involved in the photocurrent process are also discussed.