Epitaxial Growth of InGaN Multiple-Quantum-Well LEDs With Improved Characteristics and Their Application in Underwater Optical Wireless Communications

InGaN light-emitting diodes (LEDs) grown with a thin GaN barrier and a gradually reduced well width in the multiple-quantum-well (MQW) regions close to n-GaN are proposed for use in underwater optical wireless communications. Experimentally, LED epiwafers grown by metal-organic vapor phase epitaxy were found to have comparable crystalline quality despite using a different epistructure design from InGaN MQWs. The modified MQWs facilitated hole transport to the deep quantum wells while preventing energetic electrons from accumulating at the topmost quantum wells close to p-GaN, thus improving the current-light output performance at high currents. In addition, relatively strong carrier localization in the proposed LEDs indicates more injected carriers within the modified MQWs can participate in radiative recombinations to contribute to light output. On the other hand, the available bandwidth of a line-of-sight LED-based optical link passing through a 100-cm-long water tank was found to be around 148.7 MHz using the proposed LED, which is 1.3× higher than that obtained using normal LED. This type of optical link produces data transmission at rates in tap water exceeding 300 Mbit/s and enables real-time transmission of digital TV signals.