ANALYSIS OF LATTICE-DISTORTIONS IN HIGH-QUALITY INGAASP EPITAXIAL OVERGROWTH OF RECTANGULAR-PATTERNED INP GRATINGS

The crystalline quality of InGaAsP deposited via gas-source molecular beam epitaxy on rectangular-patterned InP substrates has been investig ated. Triple axis x-ray diffractometry measurements of InGaAsP deposit ed on planar InP substrates confirm that the pseudomorphic epilayer co mposition is uniform and of high-crystalline quality. Triple axis x-ra y diffraction.analysis of InGaAsP deposited on rectangular-patterned s ubstrates reveals that the crystalline quality of the epilayer is not compromised by the presence of the grating. Symmetric [(004)] and asym metric [(224)] reciprocal space maps of overgrown rectangular gratings indicate that both the InP.and InGaAsP within the grating region exhi bit an overall orthorhombic lattice distortion: Comparison of (004) di ffraction scans with dynamical computer simulations suggests that the distortions are not related to detectable compositional grating. The m agnitude of the orthorhombic strain, introduced by the rectangular-pat terned grating, will alter the refractive index of both materials by a mounts that are not expected to compromise the operation of optical de vices. (C) 1998 American Vacuum Society.