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Monolithic all-GaN 2T1C-μLED–photodetector integration

29 d ago

Two researchers from Shandong University, China, Yipin Gao and Chao Liu, have reported the monolithic integration of all-gallium nitride (GaN) circuits comprising two transistors (2T), one capacitor (1C), a micro-light-emitting diode (μLED), and a photodetector (PD). The work was published online in ACS Photonics on 22 May 2026. This integration creates ultra-compact pixel units with all components and spacing in the micrometer range, avoiding extra optics and system volume. Each unit can potentially serve as a pixel-level optical transceiver, supporting the convergence of micro-display and optical communication for next-generation portable and wearable intelligent terminals. During normal display operation, high-speed modulation signals can be superimposed on data lines without disturbing steady-state brightness, enabling simultaneous light emission and detection. The monolithic structure eliminates issues associated with silicon CMOS or thin-film transistor micro-displays, such as thermal mismatch, alignment inaccuracy, and parasitic degradation of system reliability and high-frequency performance, offering a simplified path to high-density arrays and display-sensing-communication integrated terminals. The 2T1C architecture, a core building block of active-matrix displays, provides high brightness, enhanced grayscale control, and low power consumption. The fabricated circuits included two 20μm×20μm transistors, one 40μm×40μm μLED, and one 40μm×40μm PD, with a 30μm LED-PD separation. The high-electron-mobility transistor (HEMT) AlGaN/GaN layers were grown by metal-organic chemical vapor deposition on 4-inch substrates. μLED and PD multiple quantum well structures were formed by inductively coupled plasma etching and MOCVD regrowth. Electrical isolation involved mesa etching, and contacts used annealed titanium/aluminium/nickel/gold for n-type and ohmic regions, indium tin oxide for current spreading, and titanium/platinum/gold for gates. The bottom capacitor electrode was formed from gate metals, and a 600nm SiO2 layer served as passivation and capacitor dielectric. Circuits were completed with titanium/nickel/gold stacks for p-electrodes and top capacitor electrode. Dynamic switching response tests at 5kHz confirmed synchronized operation, validating basic functionalities for simultaneous light emission and detection in ultra-compact footprints.