Molecular beam epitaxial regrowth on diffraction gratings for vertical-cavity, surface-emitting laser-based integrated optoelectronics

Abstract

Epitaxial regrowth techniques, using molecular beam epitaxy, were optimized for the inclusion of submicron diffraction gratings within a vertically resonant structure. Various growth conditions including chemical surface preparation, growth rate, and regrown interfacial structure were studied to determine the quality of the regrown materials and structures. Characteristics such as dislocation density and growth planarity (flatness of the regrown layers) were of particular importance due to the vertical geometry and resonance requirements of the structure. Threading dislocation densities of ≈3×106cm−2 were measured, by means of transmission electron microscopy, in the regrown structures using optimized regrowth processes. Layer thickness variations, due to growth on nonplanar surfaces (diffraction gratings), were characterized using modeling and optical reflectometry. With these results, inclusion of diffraction gratings has been demonstrated with the accurate control over layer thickness needed for use in vertically oriented devices such as vertical-cavity, surface-emitting lasers, and resonant cavity photodetectors.

Three-dimensional integration of VCSEL-based optoelectronics

“…Three different structures were used to determine their effect on the regrown material [8]. The regrown structures consisted of the following: a 100 nm, Al 0.46 Ga 0.54 As superlattice, composed of alternating layers of AlAs and GaAs, grown at a slow growth rate, the same superlattice, but grown at a fast growth rate, and no superlattice structure.…”

“…The remaining portion of the epitaxial structure was then regrown using MBE. To achieve high quality regrown material and improve planarization over the patterned surface, the fi rst 100 nm of the upper waveguide clad was grown using a superlattice with a slow growth rate and an effective alloy composition identical to the upper waveguide clad [8], as described in the previous section. waveguide, as can be seen in Figure 14.…”

“…Electron beam lithography was used to pattern the diffraction gratings in selected areas and the patterns were etched ~75 nm into the GaAs waveguide core using Cl 2 reactive ion etching (RIE). The wafer was oxygen plasma ashed and the surface was prepared for regrowth using a twostep process consisting of HCl and H 2 SO 4 [8]. The remaining portion of the epitaxial structure was then regrown using MBE.…”