Compositional dependence of in situ etching of InGaAsP materials on InP by using HCl was investigated. This investigation found that etching rates and their compositional dependence strongly depend on etching atmosphere. The introduction of AsH3 to PH3 significantly reduces etching rate. Furthermore, etching rate decreases with the compositional wavelength of InGaAsP under AsH3/PH3, while they are independent of the compositional wavelength under PH3. These experimental results can be qualitatively explained by the suppression of the desorption of arsenic atoms when these atoms exists in the etching atmosphere. Arsenic atoms thus play an important role in the in situ etching of the InGaAsP material system. Moreover. it was found good surface morphology for all compositional wavelengths when the etching temperature was reduced to 500degreesC. This is probably due to the suppression of the additional reaction between InCl or GaCl and arsenic or phosphorous atoms by lowering etching temperature. These findings are very useful for the application of in situ etching to the practical device fabrication based on InGaAsP materials. (C) 2004 Elsevier B.V. All rights reserved.