Color tunable inverted pyramid micro-LEDs based on nano-patterned sapphire substrates

Abstract

Color-tunable micro-scale light-emitting diodes (Micro-LEDs) can achieve full-color display in a simple and low-cost way. In this paper, we demonstrate growth of three-dimensional (3D) inverted pyramid GaN on nano-patterned sapphire substrates (NPSS). By using the sputtered AlN nucleation layer, the uniformity of the inverted pyramid has been improved to a large extent. Then, Micro-LEDs are epitaxially grown based on these inverted pyramids and fabricated to 20-100 µm devices. As the current increases from 1 to 100 A/cm2, the electroluminescence (EL) wavelength exhibits a large blueshift from 660 to 470 nm, corresponding to the dominant emission changing from polar InGaN multi-quantum-well (MQW) facets to semipolar ones. This color-tunable range almost covers 97% of the sRGB color gamut. Considering the combination of display and communication in the future internet of everything (IoE) era, the modulation bandwidths of the Micro-LEDs are measured to explore the carrier recombination rates of different facets in inverted pyramids. Different modulation bandwidths in polar and semipolar InGaN MQW have been observed at the current density above 60 A/cm2, and the highest -3 dB electro-optic bandwidth of 1.28 GHz from the latter is achieved at the current density of 25 kA/cm2.