Overgrowth of submicron-patterned surfaces for buried index contrast devices

In a wide variety of optoelectronic and photonic devices, a modulation of the refractive index is required. To increase device design flexibility, the index modulation may reside within the various layers of the device, and hence fabrication of the device will require subsequent overgrowth of the corrugation. The overgrowth of submicron-patterned surfaces (or gratings) for buried index contrast devices is reviewed. The material systems considered are (In, Ga)As on GaAs patterned substrates and the InGaAsP quaternary system on InP patterned substrates, as well as the associated inverted structure. The corrugation is typically a sawtooth-patterned surface or a rectangular-patterned surface having a relatively shallow depth (of the order of 100 nm). For sawtooth-patterned surface overgrowth, mass transport-induced alteration of the grating profile promotes the overgrowth of high crystalline quality material and also reduces compositional modulation of the overlayer. In contrast, for rectangular-patterned surface overgrowth, grating preservation provides the requisite (100)-oriented crystallographic planes such that compositional modulation is minimized. Furthermore, for closely lattice-matched conditions, the materials within the rectangular-patterned grating region experience an orthorhombic strain in order to elastically accommodate the lattice mismatch.