epitaxial and polycrystalline layers of silicon and silicon - germanium alloys are selectively grown on a semiconductor substrate or wafer by forming over the wafer a thin film masking layer of an oxide of an element selected from scandium , yttrium , lanthanum , cerium , praseodymium , neodymium , samarium , europium , gadolinium , terbium , dysprosium , holmium , erbium , thulium , ytterbium , and lutetium ; and then growing the epitaxial layer over the wafer at temperatures below 650 ° c . the epitaxial and polycrystalline layers do not grow on the masking layer . the invention overcomes the problem of forming epitaxial layers at temperatures above 650 ° c . by providing a lower temperature process .