  We demonstrate the real-time detection of single photogenerated electrons in
two different lateral double quantum dots made in AlGaAs/GaAs/AlGaAs quantum
wells having a thin or a thick AlGaAs barrier layer. The observed incident
laser power and photon energy dependences of the photoelectron detection
efficiency both indicate that the trapped photoelectrons are, for the thin
barrier sample, predominantly photogenerated in the buffer layer followed by
tunneling into one of the two dots, whereas for the thick barrier sample they
are directly photogenerated in the well. For the latter, single photoelectron
detection after selective excitation of the heavy and light hole state in the
dot is well resolved. This ensures the applicability of our quantum well-based
quantum dot systems for the coherent transfer from single photon polarization
to single electron spin states.
