Longhyphen;range, minorityhyphen;carrier transport in high quality lsquo;lsquo;surfacehyphen;freersquo;rsquo; GaAs/AlGaAs double heterostructures

摘要

Using a novel timehyphen;resolved optical photoluminescence imaging technique, analogous to the electrical Haynesndash;Shockley experiment, we have measured roomhyphen;temperature minorityhyphen;carrier transport in a series of lsquo;lsquo;surfacehyphen;freersquo;rsquo; GaAs/Al0.3Ga0.7As double heterostructures. These measurements are only possible in lsquo;lsquo;surfacehyphen;freersquo;rsquo; samples in which the bandhyphen;tohyphen;band radiative recombination lifetimes are longminus;here up to 2.5 mgr;s. We find minorityhyphen;carrier transport to be lsquo;lsquo;diffusive,rsquo;rsquo; with diffusion lengths of up to sim;140 mgr;m. We also find transport in thick (gsim;1 mgr;m) structures to be mediated by holehyphen;dominated ambipolar diffusion, whereas for thinner structures a transition from ambipolar to freehyphen;electronhyphen;dominated diffusion is observed. These results demonstrate that our heterostructures becomeeffectivelymodulationdopedfor GaAs thicknesses lsim;1 mgr;m.