The effects of chemical etching and ambient conditions on GaAs substrates prior to epitaxial growth were investigated using a metal organic chemical vapor deposition apparatus. It was found that when an appropriately etched substrate is exposed to air, a clean substrate–epitaxial layer interface with a smooth carrier depth profile is obtained. However, when the etched substrate is exposed to dry nitrogen, a contaminated interface with a large accumulation carrier depth profile is obtained. The carrier accumulation profile of the nitrogen-exposed substrate is considered to be due to Si atoms at the interface. It was also found that impurities at the surface of the substrate exposed to dry nitrogen are not reduced by pregrowth heating. The reason why the impurities are difficult to remove can be explained in terms of a surface diffusion increase. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(10): 10–16, 2000 [ABSTRACT FROM AUTHOR]