Study of AlGaAs/GaAs quantum wells overgrown on in situ Cl-2-etched GaAs substrates

We have studied the properties of in situ Cl-2-etched GaAs surfaces and ove rgrown quantum well (QW) structures as a function of the etching temperatur e. From reflection high-energy electron diffraction, atomic force microscop y, and Auger electron spectroscopy analysis on Cl-2-etched surfaces we foun d that low etching temperatures (similar to 50 degrees C) results in Ga-ric h rough surfaces, because at these temperatures the desorption rate of Ca c hlorides is much slower than that for As chlorides. At high etching tempera tures (similar to 200 degrees C) both Ga and As chlorides can be removed, r esulting in a more stoichiometric etching which yields a smooth GaAs surfac e. The optical properties of QW structures overgrown on in situ etched surf aces were compared to those of an ex situ processed sample. For the cn: sit u processed sample we found degraded photoluminescence (PL) characteristics and a high amount of impurities. The PL properties improved, and the amoun t of impurities sharply decreased in the ill situ sample Cl-2 etched at 200 degrees C. Photoreflectance spectroscopy showed the presence of intense in ternal electric fields generated by the ex situ processing. The electric fi eld strength was reduced in the in situ Cl-2-etched samples. (C) 2000 Ameri can Vacuum Society. [S0734-211X(00)00703-4].