Characteristics of Micro‐Size Light‐Emitting Diode for Illumination and Visible Light Communication

Abstract

The white light‐emitting diode (LED) modules, in which the GaN‐based blue‐LED chip with 4 × 4 arrayed pixels are packaged with chip‐on‐board technique and welded on a print circuit board, are fabricated for both illumination and visible light communication (VLC). The effects of the mesa size on the characteristic features are explored. It shows that the pixels with small size can sustain high saturated current density. Under the saturated current density, the highest luminous flux of 278.4 lm can be obtained by using the largest pixel of 160 µm‐diameter, or the highest 3‐dB modulation bandwidth of 127.3 MHz can be obtained by using the smallest pixels of 60 µm‐diameter. In case the white‐LED module works for a long time, the injected current density should be far away from the saturated current density. On condition that the 3‐dB modulation bandwidth of 100 MHz is required, the white‐LED module with 100 µm‐diameter pixels is proposed and the luminous flux can reach 164.8 lm. Subsequently, the electrode size is optimized to get higher luminous flux. By enlarging the p‐electrode, the white‐LED module with 120 µm‐diameter pixels can achieve the luminous flux of 235.2 lm while the 3‐dB modulation bandwidth holds 100 MHz.

Thermal Effects on the Electrical and Optical Characteristics of Micro‐Light‐Emitting Diodes with Different Current Spreading Layer

“…Figure shows the forward voltages, LOPs, external quantum efficiencies (EQEs), and WLPs of the micro‐LED chips with different CSLs and different sizes at room temperature (23 °C). The variation trends of the electrical and optical characteristics for different sizes are consistent with our previous paper, for both ITO and Ni/Au CSLs. In this section, we focus on the comparison between the two CSLs.…”

“…Using commercial epitaxial wafers, the micro‐LED chips are fabricated by the conventional fabrication process . Two types of CSL are prepared.…”

“…Two types of CSL are prepared. The first type of CSL is a 100‐nm‐thick ITO, electron‐beam‐evaporated at a temperature of the carrier tray of 35 °C. In the evaporation process, no oxygen gas is injected into the chamber for the initial 16.7‐nm‐thick ITO material, while for the following 83.3 nm, the flow rate of the oxygen gas is 2 sccm.…”

“…Micro‐light‐emitting diode (micro‐LED) is a popular light source for high‐bandwidth visible‐light communication (VLC) . As its modulation bandwidth has a positive‐proportional relationship with the injected current density, the micro‐LED chip designed for VLC always operates under a large current density and suffers from large thermal effects.…”

“…Owing to the low doping concentration of the p‐type GaN epitaxial layer in the LED wafer, a high‐conductivity current spreading layer (CSL) is used. Indium tin oxide (ITO) and Ni/Au are common materials for CSLs in top‐emitting devices. The electrical and optical performances of LED chips with these two CSLs have been compared in several papers .…”