Residual Carbon and Oxygen Surface Contamination of Chemically Etched GaAs (001) Substrates

Several different cleaning procedures for GaAs (001) substrates are compared using X-ray photoelectron spectroscopy. This work emphasizes the effect of the last etching step: HCl-, HF-ethanol (10%), bromine-methanol (1%), performed on a spinner (3000 rpm) operated in a nitrogen dry box, and running deionized water (RDIW). These four etchants lead to deoxidized surfaces, although RDIW leaves a fractional coverage of sligthly bounded oxygen species (≃0.15 monolayer). The residual carbon contamination is around 0.2 monolayer whatever the etchant used and is removable by flash heating at 400°C under ultrahigh vacuum. RDIW, HCl- and HF-ethanol do not produce any significant etching of the GaAs matrix whereas bromine-methanol (1%) removes ≃0.2 µm per cm3 of solution.