Abstract
Recently, femtosecond photocurrent transients in quantum wells have been studied under various conditions using excitonic electroabsorption as a femtosecond electrical signal detector.[1] In the present case, we study femtosecond electrical signal generation in quantum wells at 77 K with a tunable 100 fs Ti:Sapphire laser for excitation and nonresonant electro-optic sampling[2] using LiTaO3. This combination is interesting because we can tune the excitation above and below the excitonic resonance and investigate the resultant photocurrent signal. It has been predicted that sub-resonant excitation of quantum wells under DC bias conditions should result in electrical signals which are as short as the optical pulse (AC-DC stark effect).[3,4] In bulk materials, in principle the same effect exists,[5] however excitations into the Franz-Keldysh tail produce a real photocurrent excitation which is undesirable, whereas the Franz-Keldysh tail is suppressed by quantum confinement in quantum wells.
© 1992 IQEC
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