Augmented reality and visual reality (AR & VR) micro-displays require micro light emitting diodes (µLEDs) with an ultra-small dimension (≤ 5 µm), high external quantum efficiency (EQE) and narrow spectral linewidth. Unfortunately, dry etching which is the most crucial step for the fabrication of µLEDs in current approaches introduces severe damages, which seems to become an insurmountable challenge for achieving ultra-small µLEDs with high EQE. Furthermore, it is well-known that µLEDs which require InGaN layers as an emitting region naturally exhibit significantly broad spectral linewidth, which becomes increasingly severe towards long wavelengths such as green. In this paper, we have reported a combination of our selective overgrowth approach developed very recently and epitaxial lattice-matched distributed Bragg reflectors (DBRs) embedded in order to address all these fundamental issues. As a result, our µLEDs with a diameter of 3.6 µm and an inter-pitch of 2 µm exhibit an ultra-high EQE of 9% at ~500 nm. More importantly, the spectral linewidth of our µLEDs has been significantly reduced down to 25 nm, the narrowest value reported so far for III-nitride green µLEDs.

This paper reports a novel voltage-controlled light emitter with fast switching speed and dimming capability using a monolithically integrated GaN HEMT-LED device. The integrated HEMT-LED device, with a transconductance of 113 mS/mm and large light emitting area (450 ×470 μm2), exhibits a fast switching speed of 15 MHz. When functioning as an optical transmitter, a data rate of 16.7 Mbit/s was demonstrated. By reducing the duty cycle of the pulsed gate voltage from 100% to 0.1%, the light intensity decreased accordingly, and a linear pulse-width modulation (PWM) dimming performance with a wide dimming range (0.1% to 100%) and high dimming ratio (51,282:1) was achieved.

We report for the first time on-chip integration of III-nitride voltage-controlled light emitters with visible and ultraviolet (UV) photodiodes (PDs). InGaN/GaN and AlGaN/GaN heterostructures were grown in specific regions by selective-area epitaxy, allowing monolithic integration of versatile devices including visible light emitting diodes (LEDs), visible-light PDs, AlGaN/GaN high electron mobility transistors (HEMTs), and UV-light Schottky barrier (SB) PDs. A serial connection between the LED and HEMT through the epitaxial layers enables a three-terminal voltage-controlled light emitter (HEMT-LED), efficiently converting voltage-controlled signals into visible-light signals that can be coupled into an adjacent visible-light PD generating electrical signals. While the integrated blue HEMT-LED and PD transmits signals carried by visible light, the visible-blind SB-PD on a chip receives external UV light control signals with negligible interference from the on-chip visible-light source. This integration scheme can be extended to open an avenue for developing a variety of applications, such as smart lighting, on-chip optical interconnect, optical wireless communication, and opto-isolators.

Visible light communications (VLC) require III-nitride visible micro-light-emitting diodes (μLEDs) with a high-modulation bandwidth. Such μLEDs need to be driven at a high injection current density on a kA/cm² scale, which is about 2 orders of magnitude higher than those for normal visible LED operation. μLEDs are traditionally fabricated by dry-etching techniques where dry-etching-induced damages are unavoidable, leading to both a substantial reduction in performance and a great challenge to viability at a high injection current density. Furthermore, conventional biasing (which is simply applied across a p–n junction) is good enough for normal LED operation but generates a great challenge for a single μLED, which needs to be modulated at a high injection current density and at a high frequency. In this work, we have proposed a concept for an epitaxial integration and then demonstrated a completely different method that allows us to achieve an epitaxial integration of a single μLED with a diameter of 20 μm and an AlGaN/GaN high-electron-mobility transistor (HEMT), where the emission from a single μLED is modulated by tuning the gate voltage of its HEMT. Furthermore, such a direct epitaxial approach has entirely eliminated any dry-etching-induced damages. As a result, we have demonstrated an epitaxial integration of monolithic on-chip μLED-HEMT with a record modulation bandwidth of 1.2 GHz on industry-compatible c-plane substrates.

Visible light communication requires III-nitride LEDs with a high modulation bandwidth but has c-plane limitations. General illumination requires green/yellow III-nitride LEDs with high optical efficiency that are difficult to achieve on c-plane substrates. Micro-LEDs with a low efficiency are used to obtain a high modulation bandwidth. This paper demonstrates a record modulation bandwidth of 540 MHz for our semi-polar green LEDs with a broad area. Semi-polar yellow and amber LEDs with a modulation bandwidth of 350 MHz and 140 MHz respectively have also been reported, and are the longest wavelength III-nitride LEDs. These results agree with differential carrier lifetime measurements.

This paper has reported a non-polar GaN metal-semiconductor-metal (MSM) photo-detector (PD) with an ultra-high responsivity and an ultra-fast response speed in the ultraviolet spectral region, which was fabricated on non-polar (11-22) GaN stripe arrays with a step-change in crystal quality grown on patterned (110) silicon substrates by means of using our two-step processes. Our non-polar GaN MSM PD exhibits a responsivity of 695.3 A/W at 1 V bias and 12628.3 A/W at 5 V bias both under 360 nm ultraviolet illumination, which are more than 20 times higher and 4 orders of magnitude higher compared with the current state-of-the art, respectively. The non-polar GaN MSM-PD displays a rise-time and a fall-time of 66 µs and 43 µs, respectively, which are three orders of magnitude faster compared with the current state-of-the-art.