Cascade GaN-based blue micro-light-emitting diodes for dual function of illumination and visible light communication

The dual function of illumination and visible light communication is a promising solution for a low-cost high-speed wireless access network. To realize high optical power and large modulation bandwidth, the cascade GaN-based top-emitting blue micro-light-emitting diode array chips are proposed. The electrical, optical, and communication performances of the series or parallel array chips with 1, 4, and 10 pixels are characterized and discussed. With increasing the number of pixels, the series configuration gives a high-voltage chip, while the parallel configuration under the same current density gives a high-current chip, in which the significantly increased flowing current causes the increased heat thereby reduces the allowable maximum current density and amplitude of the modulation voltage signals. Either series or parallel array is an efficient way to improve the optical powers. However, the average light-output powers (LOPs) and average external quantum efficiencies (EQEs) per each pixel decrease as the number of pixels increases, owing to the light absorption by adjacent pixels and the increased heat effect. Furthermore, with increasing the number of pixels, the modulation bandwidths, the bit-error rates (BERs), and the maximum data rates in series configuration are improved, while those in parallel configuration are deteriorated. Comparing to the parallel counterpart, the series configuration is preferred in the dual function system, because of its higher allowable current densities, LOPs, EQEs, and modulation bandwidths, as well as lower BERs and larger maximum data rates. The improved performance can be attributed to the reduced heats and the decreased device capacitances in the series array chips.