Disclosed is a method for preparing heteroepitaxial thin films which are free of island structures which have a bad influence on the photoelectric properties and interfacial reactivity of the thin films. These heteroepitaxial thin films are deposited on grooved or curved surfaces of substrates. The use of grooved substrates relieves the coherent elastic strain from the thin films, thereby inhibiting the surface roughening and the island structure formation in the heteroepitaxial thin films. The method can be applied to all of the thin films that show island structures, including GaAs/Si and SiGe/Si typically used in semiconductor devices and various electronic parts, enabling the thin films to be flatly deposited at a significant thickness on various substrates without additionally processing.