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Inorganic semiconductor-based microscale light-emitting diodes (micro-LEDs) have been widely considered the key solution to next-generation, ubiquitous lighting and display systems, with their efficiency, brightness, contrast, stability, and dynamic response superior to liquid crystal or organic-based counterparts. However, the reduction of micro-LED sizes leads to the deteriorated device performance and increased difficulties in manufacturing. Here, we report a tandem device scheme based on stacked red, green, and blue (RGB) micro-LEDs, for the realization of full-color lighting and displays. Thin-film micro-LEDs (size ~100 µm, thickness ~5 µm) based on III-V compound semiconductors are vertically assembled via epitaxial liftoff and transfer printing. A thin-film dielectric-based optical filter serves as a wavelength-selective interface for performance enhancement. Furthermore, we prototype arrays of tandem RGB micro-LEDs and demonstrate display capabilities. These materials and device strategies provide a viable path to advanced lighting and display systems. [ABSTRACT FROM AUTHOR]

We demonstrate the growth and optical characterization of semipolar (1 1 &2macr; 2) GaN light-emitting diodes (LEDs) on sapphire utilizing two distinct heteroepitaxial growth methodologies. The properties of semipolar (1 1 &2macr; 2) LEDs are analyzed by the simultaneous growth of LED structures on templates prepared by both two-step growth on m-sapphire and selective growth on etched r-plane sapphire. Typically, growth on m-sapphire yields a high density of microstructural defects and surface morphological features which complicate the understanding of emission properties in devices. In this study, we find improved spectral properties of devices grown on etched r-sapphire due to improved surface roughness and microstructural quality (x-ray diffraction rocking curves of 280-550 arcsec for on-axis (1 1 &2macr; 2) and off-axis (101n), n = 0-5 diffractions), and reveal that the commonly observed broad emission and sub-bandgap peak in semipolar LEDs on sapphire are caused by a tunneling-assisted radiative recombination mechanism. [ABSTRACT FROM AUTHOR]

This letter reports a two-step growth process for improving microstructural quality of semipolar (112_2) GaN on nitridized m-plane sapphire. The two-step growth of (112_2) GaN, islanding growth under high pressure followed by islands coalescence under low pressure, went through a roughening-recovery process, which was found very effective in reducing the density of stacking faults and dislocations in (112_2) GaN. The x-ray rocking curves of both on-axis and off-axis planes were narrowed down by more than 50%. The improvement of GaN quality was confirmed by a boost in blue and green optical output of semipolar (112_2) InGaN/GaN quantum wells. [ABSTRACT FROM AUTHOR]

We propose, fabricate and characterize photonic integration of a InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED), waveguide, ring resonator and InGaN/GaN MQW-photodiode on a single chip, in which the photonic circuit is suspended by the support beams. Both experimental observations and simulation results illustrate the manipulation of in-plane light coupling and propagation by the waveguide and the ring resonator. The monolithic photonic circuit forms an in-plane data communication system using visible light. When the two suspended InGaN/GaN MQW-diodes simultaneously serve as the transmitter and the receiver, an in-plane full-duplex light communication is experimentally demonstrated with a transmission rate of 30 Mbps, and the superimposed signals are extracted using the self-interference cancellation method. The suspended photonic circuit creates new possibilities for exploring the in-plane full-duplex light communication and manufacturing complex GaN-based monolithic photonic integrations. [ABSTRACT FROM AUTHOR]

This work reports a significant improvement in efficiency by optimizing the via-like n-electrode architecture design of a GaN-based thin-film LED grown on a 6-inch silicon substrate. The external quantum efficiency of the as-fabricated 1.1 mm × 1.1 mm via-thin-film LED chip at 350 mA was increased by 11.3% compared to that of a vertical thin-film LED chip with a conventional finger-like n-electrode. Detailed analysis of encapsulation gain and false color emission patterns illustrated that the significantly improved LED performance was due to enhanced light extraction efficiency and more uniform current spreading, both of which can be attributed to the optimized via-thin-film chip structure. Minimizing the light loss at the periphery of the Ag mirror was demonstrated to be a critical factor for improving light extraction, rather than simply replacing the finger-like n-electrodes with via-like ones. After encapsulation, the median blue lamp power and the wall-plug efficiency of the via-thin-film LED at 350 mA reached 659 mW and 63.7%, respectively. [ABSTRACT FROM AUTHOR]