The stark effect and electron-hole wavefunctions in InAs-GaAs self-assembled quantum dots

New information on the electron-hole wavefunctions in InAs-GaAs self-assembled quantum dots is obtained from study of the quantum confined Stark effect. From the sign of asymmetry observed in the Stark effect, it is deduced that the dots have a permanent dipole moment directed from base to apex, implying that holes are localised above the electrons in the dots. This highly unexpected electron-hole alignment is opposite to that predicted by all previous theories. We explain our results by comparison with strain/electronic structure modelling, and are able to deduce that the nominally InAs dots contain significant amounts of gallium, and have a strongly truncated shape. In the light of these results most if not all previous modelling of the electronic structure of InAs self-assembled quantum dots needs to be re-examined. The mechanisms involved in the photocurrent process employed to observe the Stark effect, and the significance of photocurrent techniques to measure absorption spectra in quantum dots are discussed.