Patent ID: 7619301

Claim:
A GaAs semiconductor substrate having a surface layer located at a surface, wherein when an atomic ratio is measured using a 3d electron spectrum of Ga atoms and As atoms measured at a condition of 10° for a photoelectron take-off angle θ by X-ray photoelectron spectroscopy, a structural atomic ratio of all Ga atoms to all As atoms (Ga)/(As) at said surface layer is at least 0.5 and not more than 0.9, a ratio of As atoms bound with O atoms to all Ga atoms and all As atoms (As—O)/{(Ga)+(As)} ratio at said surface layer is at least 0.15 and not more than 0.35, and a ratio of Ga atoms bound with O atoms to all Ga atoms and all As atoms (Ga—O)/{(Ga)+(As)} at said surface layer is at least 0.15 and not more than 0.35, and a concentration of ammonium salt adhering to said surface, wherein said concentration of ammonium salt is less than 0.4 ng/cm 2 .