Doping interface dipoles: Tunable heterojunction barrier heights and band-edge discontinuities by molecular beam epitaxy

We have succeeded for the first time in artificially tuning the conduction and valence-band barrier heights at an abrupt intrinsic semiconductor-semiconductor heterojunction via a doping interface dipole (DID). This is achieved by means of ultrathin ionized donor and acceptor sheets in situ grown within ≲100 Å from the heterointerface by molecular beam epitaxy. In the limit of a few atomic layers separation between the charge sheets this amounts to modify the effective band-edge discontinuities. A near one order of magnitude enhancement in the photocollection efficiency of an abrupt AlGaAs/GaAs heterojunction has been observed as result of the conduction-band barrier lowering induced by the DID.