Investigation of Electrical and Optical Properties of AlGaInP Red Vertical Micro-Light-Emitting Diodes with Cu/Invar/Cu Metal Substrates

This research studies the performance of n-side up thin-film AlGaInP-based vertical micro-light-emitting diodes (V- $\mu $ LEDs) with four different chip sizes, $100\times100$ , $70\times70$ , $50\times50$ , and $25\times 25\,\,\mu \text{m}^{2}$ , on a $50~\mu \text{m}$ thick composite metal (copper/Invar/copper; CIC) substrate. The LEDs were fabricated to understand the electrical and optical properties of AlGaInP V- $\mu $ LEDs as functions of chip sizes. For device performance, the small LEDs provide a larger current density under the same voltage and present smaller forward voltage, a low red-shift phenomenon, and low output power density. For the external quantum efficiency (EQE) of device, larger LEDs exhibit maximum EQE at lower current density as compared to smaller LEDs. The injection of a small current at the same current density obtains the emission image. The obtained data suggest that the smallest V- $\mu $ LEDs exude a sidewall effect that could impact the device performance.