The chemical etching behaviors of undoped GaAs (100) in tartaric acid (C_4H_6O_6) and hydrogen peroxide (H_2O_2) aqueous solutions are investigated and the role of the constituents of the etching solution (H_2O_2 and C_4H_6O_6) is reported. The etching rate of GaAs increases with increased concentration of H_2O_2. X-ray photoelectron spectroscopy studies clarify that the H_2O_2 oxidizes the GaAs surface, and C_4H_6O_6 removes the oxide layers. It seems that successive oxidation and dissolution of GaAs are performed during chemical etching in C_4H_6O_6 + H_2O_2, and gallium oxide may preferably dissolve into the solution. The concentrations of H_2O_2 and C_4H_6O_6 in the H_2O_2 + C_4H_6O_6 aqueous solutions are obtained and in-situ monitored by measurement of the absorbance at 270 nm and 250 nm, respectively. The etching rate of GaAs in the solution is also estimated by measuring absorbance at 270 nm. These findings may aid in controlling the chemical etching rate of GaAs and stabilizing the process.
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