100 fs carrier dynamics in GaAs under 100 nm diameter apertures

We study the decay of an optically excited cloud of carriers as a function of its initial diameter d. Values as low as d = 100 nm are possible via met allic apertures on bulk GaAs fabricated by electron beam lithography. We fi nd that the decay time tau versus d scales as tau proportional to d(2) for large d, as expected for diffusive transport, and as tau proportional to d for submicron values of d, indicating strong deviations from diffusive tran sport. The dependence on parameters such as initial carrier kinetic energy, carrier density and sample temperature is discussed.