Overgrowth of submicron-patterned surfaces for buried index contrast devices

In a wide variety of optoelectronic and photonic devices, a modulation of t he refractive index is required. To increase device design flexibility, the index modulation may reside within the various layers of the device, and h ence fabrication of the device will require subsequent overgrowth of the co rrugation. 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 sys tem on InP patterned substrates, as well as the associated inverted structu re. The corrugation is typically a sawtooth-patterned surface or a rectangu lar-patterned surface having a relatively shallow depth (of the order of 10 0 nm). For sawtooth-patterned surface overgrowth, mass transport-induced al teration of the grating profile promotes the overgrowth of high crystalline quality material and also reduces compositional modulation of the overlaye r. In contrast, for rectangular-patterned surface overgrowth, grating prese rvation provides the requisite (100)-oriented crystallographic planes such that compositional modulation is minimized. Furthermore, for closely lattic e-matched conditions, the materials within the rectangular-patterned gratin g region experience an orthorhombic strain in order to elastically accommod ate the lattice mismatch.