Analysis of lattice distortions in high-quality InGaAsP epitaxial overgrowth of rectangular-patterned InP gratings

Abstract
The crystalline quality of InGaAsP deposited via gas-source molecular beam epitaxy on rectangular-patterned InP substrates has been investigated. Triple axis x-ray diffractometry measurements of InGaAsP deposited on planar InP substrates confirm that the pseudomorphic epilayer composition is uniform and of high-crystalline quality. Triple axis x-ray diffraction analysis of InGaAsP deposited on rectangular-patterned substrates reveals that the crystalline quality of the epilayer is not compromised by the presence of the grating. Symmetric [(004)] and asymmetric [(224)] reciprocal space maps of overgrown rectangular gratings indicate that both the InP and InGaAsP within the grating region exhibit an overall orthorhombic lattice distortion. Comparison of (004) diffraction scans with dynamical computer simulations suggests that the distortions are not related to detectable compositional grating. The magnitude of the orthorhombic strain, introduced by the rectangular-patterned grating, will alter the refractive index of both materials by amounts that are not expected to compromise the operation of optical devices.