The ternary InxGa1-xN alloy system is a promising monolithic material platform for next-generation and high-resolution RGB display technologies, owing to its tunable bandgap and robust optoelectronic properties. A prominent hurdle to commercialization lies in the considerable lattice mismatch between GaN and In-rich long-wavelength quantum wells, leading to catastrophic compressive stress that degrades material quality and elicits high piezoelectric fields, separating charge carriers and reducing radiative recombination rates. Recent promising mitigation efforts have focused on strain templating, wherein LED heterostructure growth is templated by a strain-relaxed, lattice-expanded buffer that reduces nominal GaN/InGaN lattice mismatch.
This talk will explore recent efforts to reduce lattice mismatch by encouraging Poisson relaxation in partially relaxed semipolar InGaN epilayers (relaxed InGaN buffers, or RIBs) through micro- and nanopatterning. A thick In0.06Ga0.94N buffer layer grown with metalorganic chemical vapor deposition (MOCVD) on free-standing (11-22) GaN substrates was patterned with colloidal lithography, forming micro- and nanopillars with aspect ratios of 1:4 and 1:2 (height:diameter), respectively. These patterned buffers showed commensurate degrees of biaxial relaxation as verified by X-ray diffraction (XRD) and cathodoluminescence (CL) measurements. A suite of microscopic and spectroscopic (XRD, PL/CL) methods were then used to probe the emission quality from subsequently grown blue-emitting QW layers and deconvolve the effects of faceting and quantum well thickness; a red-shifted emission profile with orders-of-magnitude defect reduction was observed on patterned buffer structures relative to planar InGaN buffer layers.