Self-contained InGaN/GaN micro-crystal arrays as individually addressable multi-color emitting pixels on a deformable substrate

Abstract

InGaN/GaN micro-crystals (μ-crystals) are self-contained and individually-addressable light emitting crystals that have unique potential in the development of ultra-small and ultra-high resolution pixels for next-generation displays. In this study, we explore the electrically-driven light emission behavior of vertically standing InGaN/GaN micro-crystals (μ-crystals) with well-defined crystal facets and tunable size. InGaN/GaN μ-crystals have hollow pedestals weakly bound to the substrate surface, thus enabling individual manipulation and/or collective transfer to other target surfaces. Cyclic bending tests and finite element analysis (FEA) of the strain distribution further highlight the excellent mechanical deformability of a device layout consisting of μ-crystal pixels embedded in a polymeric matrix. Light-emitting diodes (LEDs) with individual InGaN/GaN μ-crystals exhibit strong electroluminescence (EL) with unique features such as variations in emission spectra with respect to crystal diameter and driving voltage bias. Comparative analyses of photoluminescence, cathodoluminescence, and electric potential simulation indicate a strong correlation between the EL wavelengths and dominant emitting regions of InGaN/GaN polyhedral crystal planes. This is further supported by scanning transmission electron microscopy of quantum well structures, which strongly depend on both size and the crystal facets.