Near-infrared electroluminescence of InGaN quantum dots (QDs) formed by controlled growth on photoelectrochemical (PEC) etched QD templates is demonstrated. The QD template consists of PEC InGaN QDs with high density and controlled sizes, an AlGaN capping layer to protect the QDs, and a GaN barrier layer to planarize the surface. Scanning transmission electron microscopy (STEM) of Stranski–Krastanov (SK) growth on the QD template shows high-In-content InGaN QDs that align vertically to the PEC QDs due to localized strain. A high-Al-content
Structural origin of the high-performance light-emitting InGaN/AlGaN quantum disks
Ternary III-nitride-based nanowires with highly efficient light-emitting properties are essential for a broad range of applications. By using the selective area molecular-beam epitaxy method, InGaN/AlGaN quantum disks (QDs) embedded in hexagonal GaN nanowires were successfully grown. With the help of atomic-scale-resolved transmission electron microscopy and atom probe tomography, atomic ordering and other related structural information, such as crystallography and local chemistry, have been unambiguously revealed to provide unique insights into the exceptionally strong photoluminescence enhancements. A boomerang-shaped InGaN/AlGaN QD was identified, and atomic-level 1 : 1 periodic chemical ordering within the boomerang shaped AlGaN layers along the c -direction was revealed, confirming the preferential site occupation of Al-atoms. This type of growth provides a strong suppression of the quantum-confined Stark effect and is thus likely a very strong contributor to the exceptional properties. This work therefore enables us to directly establish the key structural elements necessary to understand the exceptionally strong emission exhibited by these materials. Optimization of the configurations of QDs could be an alternative design tool for developing various advanced LED device applications with well-designed structure and desirable optical properties.
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- Award ID(s):
- 1709207
- PAR ID:
- 10105630
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 11
- Issue:
- 18
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 8994 to 8999
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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capping layer prevents the collapse of the SK QDs due to intermixing or decomposition during higher temperature GaN growth as verified by STEM. Growth of low-temperature (830°C) p-type layers is used to complete the p-n junction and further ensure QD integrity. Finally, electroluminescence shows a significant wavelength shift (800 nm to 500 nm), caused by the SK QDs’ tall height, high In content, and strong polarization-induced electric fields. -
Razeghi, Manijeh ; Khodaparast, Giti A. ; Vitiello, Miriam S. (Ed.)Band structure, strain, and polarization engineering of nitride heterostructures open unparalleled opportunities for quantum sensing in the infrared. Intersubband absorption and photoluminescence are employed to correlate structure with optical properties of nonpolar strain-balanced InGaN/AlGaN nanostructures grown by molecular-beam epitaxy. Mid-infrared intersubband transitions in m-plane (In)AlxGa1-xN/In0.16Ga0.84N (0.19x0.3) multi-quantum wells were observed for the first time in the range of 3.4-5.1 μm (244-360 meV). Direct and attenuated total-reflection infrared absorption measurements are interpreted using structural information revealed by high-resolution x-ray diffraction and transmission electron microanalysis. The experimental intersubband energies are better reproduced by calculations using the local-density approximation than the Hartree-Fock approximation for the exchange-correlation correction. The effect of charge density, quantum well width, and barrier alloy composition on the intersubband transition energy was examined to evaluate the potential of this material for practical infrared applications. Temperature-dependent continuous-wave and time-resolved photoluminescence (TRPL) measurements are also investigated to probe carrier localization and recombination in m-plane InGaN/AlGaN quantum wells. Average localization depths of 21 meV and 40 meV were estimated for the undoped and doped structures, respectively. Using TRPL, dual localization centers were identified in undoped structures, while a single type of localization centers was found in doped structures. At 2 K, a fast decay time of approximately 0.3ns was measured for both undoped and doped structures, while a longer decay time of 2.2 ns was found only for the undoped sample. TRPL in magnetic field was explored to examine the effect of doping sheets on carrier dynamics.more » « less
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Traditional methods for synthesizing InGaN quantum dots (QDs), such as the Stranski-Krastanov growth, often result in QD ensembles with low density and non-uniform size distribution. To overcome these challenges, forming QDs using photoelectrochemical (PEC) etching with coherent light has been developed. Anisotropic etching of InGaN thin films is demonstrated here with PEC etching. InGaN films are etched in dilute H2SO4 and exposed to a pulsed 445 nm laser with a 100 mW/cm2 average power density. Two potentials (0.4 V or 0.9 V) measured with respect to an AgCl|Ag reference electrode are applied during PEC etching, resulting in different QDs. Atomic force microscope images show that while the QD density and sizes are similar for both applied potentials, the heights are more uniform and match the initial InGaN thickness at the lower applied potential. Schrodinger-Poisson simulations show that polarization-induced fields in the thin InGaN layer prevent positively charged carriers (holes) from arriving at the c-plane surface. These fields are mitigated in the less polar planes resulting in high etch selectivity for the different planes. The higher applied potential overcomes the polarization fields and breaks the anisotropic etching.
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We have demonstrated full-color and white-color micro light-emitting diodes (μLEDs) using InGaN/AlGaN core-shell nanowire heterostructures, grown on silicon substrate by molecular beam epitaxy. InGaN/AlGaN core-shell nanowire μLED arrays were fabricated with their wavelengths tunable from blue to red by controlling the indium composition in the device active regions. Moreover, our fabricated phosphor-free white-color μLEDs demonstrate strong and highly stable white-light emission with high color rendering index of ~ 94. The μLEDs are in circular shapes with the diameter varying from 30 to 100 μm. Such high-performance μLEDs are perfectly suitable for the next generation of high-resolution micro-display applications.more » « less
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In this paper, we report the molecular beam epitaxy-grown InGaN-quantum disks embedded within selective area epitaxy of GaN nanowires with both Ga- and N-polarities. A detailed comparative analysis of these two types of nanostructures is also provided. Compared to Ga-polar nanowires, N-polar nanowires are found to exhibit a higher vertical growth rate, flatter top, and reduced lateral overgrowth. InGaN quantum disk-related optical emission is observed from nanowires with both polarities; however, the N-polar structures inherently emit at longer wavelengths due to higher indium incorporation. Considering that N-polar nanowires offer more compelling geometry control compared to Ga-polar ones, we focus on the theoretical analysis of only N-polar structures to realize high-performance quantum emitters. A single nanowire-level analysis was performed, and the effects of nanowire diameter, taper length, and angle on guided modes, light extraction, and far-field emission were investigated. These findings highlight the importance of tailoring nanowire geometry and eventually optimizing the growth processes of III-nitride nanostructures.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9nr01262a
