An official website of the United States government
For the development of III-nitride-semiconductor-based monolithic micro-light-emitting diode (LED) displays, Eu,O-codoped GaN (GaN:Eu,O) is a promising material candidate for the red LEDs. The luminescence efficiency of Eu-related emission strongly depends on the local atomic structure of Eu ions. Our previous research has revealed that post-growth thermal annealing is an effective method for reconfiguring luminescent sites, leading to a significant increase in light output. We observed the preferential formation of a site with a peak at ∼2.004 eV by the annealing process. In this study, we demonstrate that it is a previously unidentified independent site (OMVPE-X) using combined excitation–emission spectroscopy and time-resolved photoluminescence measurements. In addition, we perform excitation power-dependent photoluminescence measurements and show that this OMVPE-X site dominates the emission at a low excitation power region despite its small relative abundance, suggesting a high excitation efficiency. Most importantly, applying our annealing technique to an LED exhibits a reasonably increased electroluminescence intensity associated with OMVPE-X, confirming that this site has a high excitation efficiency also under current injection. These results demonstrate the importance of OMVPE-X as a notable luminescent site for brighter and more efficient GaN:Eu,O-based LEDs.
more »
« less
III‐Nitride Micro‐LEDs for Efficient Emissive Displays
Abstract Emissive displays based on light‐emitting diodes (LEDs), with high pixel density, luminance, efficiency, and large color gamut, are of great interest for applications such as watches, phones, and virtual displays. The high pixel density requirements of some emissive displays require a particular class of LEDs that are sub‐20‐micrometers in length, called micro‐LEDs. While state‐of‐the‐art emissive displays incorporate organic LEDs, an alternative is inorganic III‐nitride LEDs with potential reliability and efficiency benefits. Here we explore the performance, challenges, and prospective outcomes for III‐nitride micro‐LEDs to produce efficient emissive displays and provide insight to advance this technology. Calculations are performed to determine the operating points for the micro‐LEDs and the efficiency of the overall emissive display. It is shown that III‐nitride micro‐LEDs suffer from some of the same problems as their larger‐sized solid‐state lighting LED cousins; however, the operating conditions of micro‐LEDs can result in different challenges and research efforts. These challenges include improving efficiency at low current densities; improving the efficiency of longer wavelength (green and red) LEDs; and creating device designs that can overcome low coupling efficiency, high surface recombination, and display assembly difficulties.
more »
« less
- Award ID(s):
- 1708227
- PAR ID:
- 10460746
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Laser & Photonics Reviews
- Volume:
- 13
- Issue:
- 9
- ISSN:
- 1863-8880
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Ultrahigh‐resolution micro light‐emitting diode (LED) displays are emerging as a viable technology for self‐emissive displays. Several of the critical issues facing micro LED displays with millions of pixels are fidelity, process control, and defect analysis during LED fabrication and transfer. Here, we investigate two non‐destructive test methods, photoluminescent and cathodoluminescent imaging, and compare them with electroluminescent images to verify LED fidelity and evaluate these methods as potential tools for defect analysis. We show that utilizing cathodoluminescent imaging as an analysis tool provides a rich data set that can identify and categorize common defects during micro LED display fabrication that correspond to electroluminescence. Photoluminescent imaging, however, is not an effective method for fidelity analysis but does provide information on dry‐etching uniformity.more » « less
-
UV‐ranged micro‐LEDs are being explored for numerous applications due to their high stability and power efficiency. However, previous reports have shown reduced external quantum efficiency (EQE) and increased leakage current due to the increase in surface‐to‐volume ratio with a decrease in the micro‐LED size. Herein, the size‐related performance for UV‐A micro‐LEDs, ranging from 8 × 8 to 100 × 100 μm2, is studied. These devices exhibit reduced leakage current with the implementation of atomic layer deposition‐based sidewall passivation. A systematic EQE comparison is performed with minimal leakage current and a size‐independent on‐wafer EQE of around 5.5% is obtained. Smaller sized devices experimentally show enhanced EQE at high current density due to their improved heat dissipation capabilities. To the best of authors’ knowledge, this is the highest reported on‐wafer EQE demonstrated in <10 μm dimensioned 368 nm UV LEDs.more » « less
-
Light emitting diodes (LEDs) have wide applications from fullcolor displays to solid‐state lighting. Numerous types of luminescent materials have been explored for LEDs, ranging from inorganic semiconductors to metal complexes and quantum dots. Despite the rapid pace of development, LEDs have not achieved their full potentials in terms of performance and cost efficiency. Identifying new eco‐friendly materials for LEDs is of great interest. Recently, metal halide perovskites and perovskite‐related hybrid materials have emerged as new generation luminescent materials with unique optoelectronic properties. Here, some of our recent development of LEDs based on metal halide perovskites and perovskite‐related materials will be discussed.more » « less
-
III-Nitride light-emitting diodes (LEDs) and laser diodes (LDs) are light sources covering ultraviolet (UV) and visible spectral regimes, which offer benefits including compact size, wavelength tuning, long lifetime, and sustainability. UV light sources have a range of applications in the fields of biology and medicine, such as sterilization and the purification of both water and air, where visible light emitters have been used in miniaturized photonic devices for optogenetic applications and other light-based therapies. Those III-Nitride light sources provide tremendous potential to be integrated with silicon (Si)-based lab-on-a-chip (LOC) technology, which typically requires the coupling of an external light source through fiber optic cable, limiting the field deployment of the devices. Integrating an on-chip III-Nitride light source with these devices opens the door to complete LOC technology, allowing for the simultaneous detection of multiple bio agents on a single platform without the need for external photonic sources. While most integrated microsystems still rely on wafer bonding at the device or wafer level, one promising method to achieve the integration of III-nitride UV and visible LEDs and LDs with conventional Si photonics and complementary metal-oxide-semiconductor (CMOS) platforms is through the use of micro-transfer printing (µTP). µTP has greater tolerances in alignment than techniques such as flip-chip integration and allows for the transfer of many devices at once. Additionally, the µTP process does not call for the complex and high temperature processing required for standard wafer bonding or necessitate complicated growth and lattice matching needed for monolithic integration. To enable µTP, an elastomeric, such as polydimethylsiloxane (PDMS), is utilized to create a transfer stamp that is employed for the precise selection of fabricated semiconductor devices for transfer from a source wafer to a target wafer. III-Nitride LEDs or LDs epitaxial structures are grown on a source wafer and fabricated through the creation of tethered coupons, or individual devices. This is accomplished by utilizing III-nitride materials grown on (111) Si. These devices can be fabricated through standard lithography and etching processes, etching down to the (111) Si substrate. A larger mesa can be patterned and etched into the Si substrate, exposing the sidewalls for wet chemical etching. The finished devices are then encapsulated in SiNxthrough plasma enhanced chemical vapor deposition (PECVD), which is patterned through standard lithography to define tethers and anchors for the subsequent wet etch. The fabricated devices are oriented in such a way as to take advantage of the difference in etch rates (>100x) of Si(110) and Si(111) in potassium hydroxide (KOH), where etching proceeds along the <110> direction. After KOH etching, the devices are left encapsulated in SiNxand suspended over the silicon substrate with an air gap, while the anchors and tethers are left largely unaffected.This enables the elastomer stamp to press down, breaking the tethers, and releasing the device. The stamp is then able to transfer the device to a target wafer that has been coated and patterned with InterVia, a spin-on dielectric material that acts as an adhesion layer. The stamp is pressed into the target wafer in such a way that the device is adhered to the target and released from the elastomer stamp. This technique can be applied to LEDs and LDs grown on (111) Si, allowing for the heterogeneous integration of III-nitride LED and LDs with conventional CMOS and Si photonic integrated circuits (PICs) as on-chip light sources, opening the door to complete LOC technology without the need for additional external photonic sources.more » « less
