Growth of embedded photonic crystals for GaN-based optoelectronic devices

摘要

We present three different techniques to fabricate embedded photonic crystals in GaN-based structures by metal organic chemical vapor deposition, geared toward high efficiency and high directionality light emitting diodes. Compared to the usual lateral epitaxial overgrowth, the novelty lies in the very short grating periods (varying from 180 to 350 nm) and the two-dimensional triangular nature of the grating. Coalescence was obtained over air-gap photonic crystals with thicknesses down to 70 nm, an essential requirement to obtain an efficient interaction between the optical guided modes and the photonic crystals. The quality and surface morphology of the overgrown layers were assessed by transmission electron microscopy and atomic force microscopy measurements. The thin coalesced GaN layer presented a fairly smooth surface (rms roughness of 1.27 nm for a 20 × 20 μm~2 scan) with no extra defects created by the embedded photonic crystals.