Contents 1. Introduction
Owing to many performance advantages over common-use technologies, micro light emitting diodes (μ-LEDs) are the promising candidate for next generation display technology [1]–[4]. Red-green-blue (RGB) μ-LEDs can be assembled to achieve full color displays using mass transfer process; however, there are still some challenges in terms of low transfer yield, slow throughput and high manufacturing cost [5]. To overcome these challenges, color conversion based on quantum dots (QDs) which requires a blue or UV-LEDs as pumping source is adopted but commercial UV-LEDs are grown on c-plane sapphire substrate. In recent years, micro-LEDs have received considerable attention for applications in next-generation displays and visible light communication (VLC) due to their fast response, light weight, low power consumption, high brightness, and high efficiency [6], [7]. GaN based LEDs grown on c-plane substrates suffer from efficiency droop caused by quantum confined Stark Effect (QCSE) resulting from polarization related electric field [8], [9]. GaN is a hexagonal crystal with a structure of wurtzite symmetry, the highest structure consistent with spontaneous piezoelectric polarization. Owing to spontaneous and piezoelectric polarization, as c -plane- grown GaN materials are subject to high built-in electric fields. LEDs based on c-plane epitaxial wafers can only work at low current densities as the current density increases due to the substantial decrease in efficiency. A better way to reduce this is to address the origin of the crystal plane’s polarization field, so growing LED devices on semipolar planes is a well-known approach to droop reduction [10], [11]. Colloidal quantum dots (QDs) is suitable to use as a color conversion layer for μ-LEDs, and a high contrast ratio can be achieved with QD-based μ-LED displays [12], [13].
