Patent ID: 7737043

Claim:
A surface treatment method of a compound semiconductor substrate to obtain the compound semiconductor substrate comprising: a step of preparing a compound semiconductor substrate, a step of polishing said compound semiconductor substrate, a step of washing said compound semiconductor substrate using an acid-mixed alkaline solution of at least 8.0 in pH, having acid ions added, and a step of washing said compound semiconductor substrate using an acid solution formed of at least one of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, and organic acid, after said step of polishing and said step of rinsing using said acid-mixed alkaline solution wherein the compound semiconductor substrate comprising: at least one of GaAs, InP, GaN, and InN; and a surface roughness Rms of not more than 0.2 nm, the surface roughness measured by an atomic force microscope at a pitch of not more than 0.4 nm in a scope of not more than 0.2 pm square.