Optical characterization of strained III-V compound semiconductor epilayers

A technique using photoluminescence spectroscopy (PL) to optically characterize the strain present in a lattice mismatched III-V compound semiconductor bulk epilayer is described. The 15-K PL spectra of a series of In_xGa_1-xAs epilayers with indium compositions at or slightly above that needed to satisfy the lattice matching condition are presented. At the exact lattice matching condition, a single, narrow, strong PL peak is observed. As the indium composition is increased further, the lattice constant increases, and the epilayer experiences biaxial compressive strain. A doublet structure evolves in the PL spectrum, and only a weak, single, broad, PL peak is observed when the whole epilayer has relaxed. The analysis is non-destructive, rapid, and applicable to any epilayer in which strain may be present