Hieu Pham Trung Pham Trung Nguyen1, Ravi Teja Velpula1 and Barsha Jain1
© 2022 ECS – The Electrochemical Society
ECS Meeting Abstracts, Volume MA2022-02, D01: Semiconductors, Dielectrics, and Metals for Nanoelectronics 19Citation Hieu Pham Trung Pham Trung Nguyen et al 2022 Meet. Abstr. MA2022-02 819DOI 10.1149/MA2022-0215819mtgabs
Author affiliations
1 New Jersey Institute of Technology
ORCID iDs
Hieu Pham Trung Pham Trung Nguyen https://orcid.org/0000-0003-1129-9581
Barsha Jain https://orcid.org/0000-0001-8957-0103
Abstract
High efficiency, high color rendition, and low-cost light-emitting diodes (LEDs) with low power consumption, long lifetime, and high reliability are highly expected for general lighting illumination, smartphones, smartwatches, virtual reality (VR), augmented reality (AR) headsets, and micro-display applications. Nonetheless, the achievement of deep green to red-emitting LEDs using conventional III-nitride quantum well heterostructures has been difficult, due to the presence of large densities of dislocations, strong polarization fields, poor hole transport, and carrier delocalization [1]. The external quantum efficiency (EQE) of the blue and green InGaN LEDs surpassed 80% and 53%, respectively. However, due to the aforementioned issues, the current InGaN red LEDs with high Indium composition exhibit extremely low EQE which is less than 3% [2]. In this regard, LEDs using nanowire structures offer dramatically reduced strain-induced polarization fields and dislocation densities, providing an ideal material structure for high-efficiency full-color and even white light emission without using phosphor converters. In this study, we have successfully designed and fabricated high-efficiency red-emitting nanowire heterostructures and demonstrated micro-LEDs with stable and strong emission at ~645 nm. Moreover, the micro-LEDs have a high internal quantum efficiency of >40%.
The InGaN/AlGaN nanowire micro-LED structures are grown by RF plasma-assisted molecular beam epitaxy (MBE) under nitrogen-rich condition. The LED structure consists of a 250 nm n-GaN nanowire template, 10 couples of 3 nm AlGaN quantum barrier (QB)/ 3 nm InGaN quantum well (QW) served as the active region, and a 200 nm p-GaN. During the epitaxial growth of AlGaN barriers, an AlGaN shell spontaneously forms, enabling a unique InGaN/AlGaN core-shell structure [3]. The emission color of the micro-LEDs can be defined by controlling the ratio of Ga/In flux and the substrate temperature during the MBE growth process. Detailed growth conditions and the device fabrication can be found elsewhere [3-5]. The nanowires are uniformly arranged on Si substrates, as illustrated in Figure 1(a). Figure 1(b) shows the schematic structure of the fabricated micro-LEDs. Strong red emissions were measured from the InGaN/AlGaN core-shell LEDs, as shown in Figure 1(c). At injection current of 400mA, the peak emission wavelength is at ~645nm. The red-emitting micro-LEDs exhibit stable emissions with a blue-shift of only ~ 4nm under injection current from 50 mA to 400 mA, attributed to the significantly reduced quantum-confined Stark effect (QCSE) in the nanowire structures. Moreover, full color micro-LEDs with device size from 10×10 µm2 to 100×100 µm2 have been fabricated using similar approach. Such high efficiency, high color rendering properties, and low power consumption micro-LEDs are promising candidates for emerging AR/VR devices and micro-LED display applications.
References: 1. Kim, M.H., et al., Applied Physics Letters, 91 (2007) 183507; 2. Liu, X., et al., Photonics Research, 10 (2022) 587; 3. Philip, M.R., et al., Journal of Vacuum Science & Technology B, 35 (2017)02B108; 4. Bui, H.Q.T., et al., Micromachines, 10 (2019) 492; 5. Jain, B., et al., Optics Express, 28(2020) 665.
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