This study focuses on developing a dual-functional visible light communication (VLC) chip utilizing micro-LED (μ-LED) suspended membrane circular arrays to address the performance limitations of conventional LEDs in high-speed optical communication. Through the design and fabrication of μ-LED arrays in different dimensions (20, 30, and 40 μm), the research examines the dimensional effects on light emission and detection performance, maximizing modulation bandwidth and optoelectronic conversion efficiency. The implementation of a suspended membrane structure and multiple-input multiple-output (MIMO) technology enhances data transmission rates and communication capacity while integrating emission and detection capabilities, establishing foundational support for dual-functional VLC systems. This study advances duplex VLC technology, particularly in optoelectronic performance and transmission rates, highlighting the significant potential of μ-LED arrays in high-speed optical communication and detection applications.

The chip fabrication utilized a 2-inch (5.08 cm) Si substrate GaN epitaxial wafer, with GaN epitaxial layers grown via metal-organic chemical vapor deposition (MOCVD) technology. The epitaxial layer measures approximately 4.575 μm in total thickness, comprising a 0.7 μm AlN/AlGaN buffer layer, a 0.8 μm undoped GaN (u-GaN) layer, a 2.8 μm n-GaN layer, a 100 nm (In)GaN layer, a 50 nm multi-quantum well (MQWs) active layer, and a 125 nm p-GaN layer. The Si substrate was thinned to 200 μm to facilitate removal. The fabrication process encompassed several critical steps: 1) Deposition of a 20 nm/100 nm Ni/Au metal layer on the p-GaN layer for p-type ohmic contact electrode formation. 2) Implementation of photolithography, ion beam etching (IBE), and inductively coupled plasma (ICP) etching to create circular μ-LED arrays in three dimensions (diameters: 20, 30, and 40 μm), exposing the n-GaN layer during ICP etching. 3) Deposition of a 50 nm/100 nm/100 nm Ti/Pt/Au metal layer on the exposed n-GaN layer to form the n-type ohmic contact electrode. 4) Application of a 200 nm SiO₂ insulating layer via plasma-enhanced chemical vapor deposition (PECVD), followed by photolithography and reactive ion etching (RIE) to establish pad openings for electrode connection. 5) Post-pad layer deposition and photoresist removal, application of new photoresist for surface protection, followed by photolithography for Si substrate etching window creation. Deep silicon etching technology facilitated Si substrate removal, establishing the suspended membrane μ-LED chip. 6) Following surface cleaning, the chip was mounted on a printed circuit board (PCB) and equipped with an SMA interface for subsequent analysis. The fabrication process yielded a dual-functional VLC chip demonstrating notable advantages in both emission and detection capabilities. Smaller arrays exhibited superior high-speed data transmission, while medium-sized arrays demonstrated optimal signal quality as photodetectors, featuring minimal jitter and waveform distortion for enhanced sensitivity and detection precision. This research provides comprehensive theoretical and experimental validation for dual-functional VLC system development.

Sample A1 demonstrates enhanced capacitance characteristics, with higher peaks and lower valleys, indicating accelerated capacitance reduction and superior carrier recombination efficiency and response speed compared to other samples. This enhanced response capability is essential for high-speed optical communication, enabling elevated modulation frequencies and improved data transmission rates [Fig. 4(c)]. The reduced LED dimensions contribute to lower parasitic capacitance, decreasing the RC time constant (τ_RC) and expanding the 3 dB bandwidth. Experimental data confirms that sample A1 achieves the highest modulation bandwidth at 8.08 MHz, while samples A2 and A3 reach 7.27 MHz and 6.75 MHz, respectively. Consequently, sample A1, characterized by higher current density (J), reduced parasitic capacitance, and superior bandwidth, presents optimal characteristics for VLC systems [Fig. 4(f)]. The optical extraction efficiencies are measured at: A1 ~84%, A2 ~77%, and A3 ~80%, substantially surpassing traditional GaN-based LEDs on silicon substrates, which typically achieve less than 40%. This enhancement demonstrates the suspended membrane array structure’s significant contribution to optical extraction efficiency, validating its effectiveness in LED performance enhancement [Fig. 5(d)]. Furthermore, Fig. 8(h) illustrates the correlation between communication rate and waveform distortion for sample A2. Utilizing DMT-modulated signals, sample A2 achieved 158.369 kbit/s under 64-QAM modulation, doubling the communication speed compared to PRBS signals. The integration of MIMO technology, employing four sector LED arrays in parallel, enables further detection speed enhancement through spatial multiplexing, optimizing system performance [Fig. 8(h)].

This study presents the design, fabrication, and evaluation of a suspended circular blue μ-LED array. Through the implementation of backside processing technology to fully remove the Si substrate, the optoelectronic performance of GaN-based μ-LEDs demonstrated substantial enhancement. The research team fabricated μ-LED chips with three different dimensions (D=20, 30, and 40 μm), designated as samples A1, A2, and A3. The LED arrays incorporate an innovative circular structure that combines light emission and detection capabilities. Sample A1 attained a data transmission rate of 79.3 Mbit/s at 460 nm, surpassing sample A3 by a factor of two. Sample A2 exhibited superior performance in 395 nm light detection, achieving a detection rate of 158.4 kbit/s, which is twice that of sample A1. The experimental findings demonstrate the size-dependent characteristics of circular μ-LED arrays in dual-function VLC: smaller μ-LEDs, particularly sample A1, demonstrate reduced parasitic capacitance, minimized sampling distortion, and enhanced noise margin, thereby improving signal fidelity and broadening modulation bandwidth. Utilizing DMT modulation, sample A1 functioning as a light emitter achieved a maximum data rate of 79.3 Mbit/s under 32-QAM modulation, validating its capability for high-speed transmission. Sample A2, operating as a light detector, delivered optimal signal quality with minimal jitter and waveform distortion, ensuring superior sensitivity and detection precision. This research demonstrates the successful single-chip integration of μ-LEDs and PDs while establishing a comprehensive theoretical and experimental foundation for developing high-speed dual-function VLC systems, offering valuable insights for future single-chip duplex VLC applications.