We have studied the properties of in situ Cl-2-etched GaAs surfaces and overgrown quantum well (QW) structures as a function of the etching temperature. From reflection high-energy electron diffraction, atomic force microscopy, and Auger electron spectroscopy analysis on Cl-2-etched surfaces we found that low etching temperatures (similar to 50 degrees C) results in Ga-rich rough surfaces, because at these temperatures the desorption rate of Ca chlorides is much slower than that for As chlorides. At high etching temperatures (similar to 200 degrees C) both Ga and As chlorides can be removed, resulting in a more stoichiometric etching which yields a smooth GaAs surface. The optical properties of QW structures overgrown on in situ etched surfaces were compared to those of an ex situ processed sample. For the cn: situ processed sample we found degraded photoluminescence (PL) characteristics and a high amount of impurities. The PL properties improved, and the amount of impurities sharply decreased in the ill situ sample Cl-2 etched at 200 degrees C. Photoreflectance spectroscopy showed the presence of intense internal electric fields generated by the ex situ processing. The electric field strength was reduced in the in situ Cl-2-etched samples.