Characterization of the internal properties of InGaN/GaN core-shell LEDs

Abstract

In this paper, we present the structural, optical, and electrical characterization of InGaN/GaN core-shell micro-LED structures selectively grown by metal organic vapor phase epitaxy (MOVPE) in arranged arrays. In particular we analyze the core-shell geometry of the pillars, consisting of a fivefold InGaN/GaN multiple quantum well and a p-type layer on all sidewall and top facets. Additionally we analyze the optical properties of the structure and the active region with high spatial resolution by cathodoluminescence. Electron beam induced current measurements (EBIC) are performed using an SEM based manipulator setup, giving proof of the presence of a depletion region as well as the intended doping polarity of the n-type core and a p-type shell wrapped around the whole structure. Using a p-n-p configuration also current crowding is discussed by EBIC and electroluminescence is demonstrated by measuring emission patterns from single core-shell structures. Color overlay of SE image (grey, FOV = 12.7 μm) and EBIC image (red) of a cleaved core-shell LED pillar contacted by two probe tips at a substrate tilt of 30°. Spatially resolved structural, optical and electrical characterization of single InGaN/GaN micro LEDs with core-shell geometry is reported and discussed. Employing point contacts the depletion region inside the LED is visualized by electron beam induced current in pn- and pnp-configurations, proving the intended p- and n-type doping. Based on these results the authors discuss current crowding effects and demonstrate electroluminescence of a single structure inside a 3D-LED array.