Angle resolved hard x-ray photoelectron spectroscopy study of the elemental composition of InGaP micro-LED sidewalls

The ternary III/V semiconductor InGaP is a leading material for the fabrication of red micro-light-emitting diode (LED) structures. Micro-LEDs are promising candidates for next-generation displays, with many advancements over current display technologies, such as high brightness and durability. Etching processes, used to define the mesa structures of the micro-LEDs and the subsequent oxidation of the mesa sidewall, can introduce surface defect states that result in non-radiative recombination on the mesa sidewall. With downward dimensional scaling of micro-LEDs, the properties of the etched mesa sidewall surfaces on the periphery of the devices play an increasingly important role in the optical performance of the structures due to increasing surface area to volume ratio. Direct measurement of the elemental composition and oxidation state of the mesa sidewall surface following etching is an essential step toward maximising the quantum efficiency of the devices. In this study, a novel measurement geometry is employed to isolate and directly characterise the elemental composition and oxidation state of micron-scale LED mesa sidewalls using angle resolved hard x-ray photoelectron spectroscopy. We show that the chemical composition of the etched sidewall is quantifiably different from that of a planar blanket-etched surface of the same material, demonstrating that planar etch studies are not a reliable proxy for sidewall composition, and establishing a measurement capability with which to evaluate future sidewall passivation treatments.