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.
We built a test system to pick up the pattern of light beam from the VCSELs and the EL spectrum simultaneously in order to study the mode behavior when the current applied on the device increased. As a result, we observed that the light spots from the VCSEL seemd to be high-order-mode while its EL spectrum included more than one peak wavelength. Comparing it with the high-order-mode case that we met and defined in VCSELs before, we considered that the mode we observed this time was different from the true high-order-mode in essence. We named it as pseudohigh-order-mode and gave the explanation.
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