Nanophotonics at Sandia: Tailoring Propagation Emission and Topological behavior of Light
Abstract not provided.
Publications
Deterministic Placement of Quantum-Size Controlled Quantum Dots for Seamless Top-Down Integration
ACS Photonics
We demonstrate a new route toward the integration and deterministic placement of quantum dots (QDs) within prepatterned nanostructures. Using standard electron-beam lithography (EBL) and inductively coupled plasma reactive-ion etching (ICP-RIE), we fabricate arrays of nanowires on a III-nitride platform. Next, we integrate QDs of controlled size within the prepatterned nanowires using a bandgap-selective, wet-etching technique: quantum-size-controlled photoelectrochemical (QSC-PEC) etching. Low-Temperature microphotoluminescence (μ-PL) measurements of individual nanowires reveal sharp spectral signatures, indicative of QD formation. Further, internal quantum efficiency (IQE) measurements reveal a near order of magnitude improvement in emitter efficiency following QSC-PEC etching. Finally, second-order cross-correlation (g(2)(0)) measurements of individual QDs directly confirm nonclassical, antibunching behavior. Our results illustrate an exciting approach toward the top-down integration of nonclassical light sources within nanophotonic platforms.
Visible Quantum Nanophotonics
The goal of this LDRD is to develop a quantum nanophotonics capability that will allow practical control over electron (hole) and photon confinement in more than one dimension. We plan to use quantum dots (QDs) to control electrons, and photonic crystals to control photons. InGaN QDs will be fabricated using quantum size control processes, and methods will be developed to add epitaxial layers for hole injection and surface passivation. We will also explore photonic crystal nanofabrication techniques using both additive and subtractive fabrication processes, which can tailor photonic crystal properties. These two efforts will be combined by incorporating the QDs into photonic crystal surface emitting lasers (PCSELs). Modeling will be performed using finite-different time-domain and gain analysis to optimize QD-PCSEL designs that balance laser performance with the ability to nano-fabricate structures. Finally, we will develop design rules for QD-PCSEL architectures, to understand their performance possibilities and limits.
Quantum Size Controlled Etching of InGaN Quantum Dots
Abstract not provided.
Ohmic contacts to Al-rich AlGaN heterostructures
Physica Status Solidi (A) Applications and Materials Science
Due to the ultra-wide bandgap of Al-rich AlGaN, up to 5.8 eV for the structures in this study, obtaining low resistance ohmic contacts is inherently difficult to achieve. A comparative study of three different fabrication schemes is presented for obtaining ohmic contacts to an Al-rich AlGaN channel. Schottky-like behavior was observed for several different planar metallization stacks (and anneal temperatures), in addition to a dry-etch recess metallization contact scheme on Al0.85Ga0.15N/Al0.66Ga0.34N. However, a dry etch recess followed by n+-GaN regrowth fabrication process is reported as a means to obtain lower contact resistivity ohmic contacts on a Al0.85Ga0.15N/Al0.66Ga0.34N heterostructure. Specific contact resistivity of 5 × 10−3 Ω cm2 was achieved after annealing Ti/Al/Ni/Au metallization.
InGaN Quantum Dots by Quantum Size Controlled Photoelectrochemical Etching
Abstract not provided.
Topological Photonic Structures for Nanophotonics
Abstract not provided.
Quantum Size Controlled Etching of InGaN Quantum Dots
Abstract not provided.
Growth of BxAl1-xN Alloys by Metalorganic Vapor Phase Epitaxy ? Towards a Lattice-Matched Ultra-Wide Bandgap Semiconductor
Abstract not provided.
Phase degradation in BxGa1−xN films grown at low temperature by metalorganic vapor phase epitaxy
Journal of Crystal Growth
Using metalorganic vapor phase epitaxy, a comprehensive study of BxGa1−xN growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750–900 °C and 20 Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to ~7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stacking faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at ~362 nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. Only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.
Nonpolar InGaN/GaN Core-Shell Single Nanowire Lasers
Nano Letters
We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.
Spatial and Compositional Dependence of Deep Level Defects in InGaN LEDs (invited)
Abstract not provided.
Improving emission uniformity and linearizing band dispersion in nanowire arrays using quasi-aperiodicity
Optical Materials Express
We experimentally investigate a new class of quasi-aperiodic structures for improving the emission pattern in nanowire arrays. Efficient normal emission, as well as lasing, can be obtained from III-nitride photonic crystal (PhC) nanowire arrays that utilize slow group velocity modes near the G-point in reciprocal space. However, due to symmetry considerations, the emitted far-field pattern of such modes are often 'donut'-like. Many applications, including lighting for displays or lasers, require a more uniform beam profile in the far-field. Previous work has improved far-field beam uniformity of uncoupled modes by changing the shape of the emitting structure. However, in nanowire systems, the shape of nanowires cannot always be arbitrarily changed due to growth or etch considerations. Here, we investigate breaking symmetry by instead changing the position of emitters. Using a quasi-aperiodic geometry, which changes the emitter position within a photonic crystal supercell (2x2), we are able to linearize the photonic bandstructure near the G-point and greatly improve emitted far-field uniformity. We realize the III-nitride nanowires structures using a top-down fabrication procedure that produces nanowires with smooth, vertical sidewalls. Comparison of room-temperature micro-photoluminescence (μ-PL) measurements between periodic and quasi-aperiodic nanowire arrays reveal resonances in each structure, with the simple periodic structure producing a donut beam in the emitted far-field and the quasi-aperiodic structure producing a uniform Gaussian-like beam. We investigate the input pump power vs. output intensity in both systems and observe the simple periodic array exhibiting a non-linear relationship, indicative of lasing. We believe that the quasi-aperiodic approach studied here provides an alternate and promising strategy for shaping the emission pattern of nanoemitter systems.
Top-Down Fabricated III-Nitride Nanowire Photonics (invited)
Abstract not provided.
InGaN Quantum Dots by Quantum Size Controlled Photoelectrochemcial Etching
Abstract not provided.
Topological Photonics Research at Sandia Labs
Abstract not provided.
Nanophotonic Structures for Topological Photonics and Quantum Light Sources (invited)
Abstract not provided.
Ohmic Contacts to Al0.85Ga0.15N/Al0.7Ga0.3N Heterostructure
Abstract not provided.
InGaN Quantum Dots by Quantum Size Controlled Photoelectrochemical Etching
Abstract not provided.
Low Etch Pit Density AlN on Sapphire
Abstract not provided.
High Brightness Room Temperature III-Nitride Based Single Photon Source
Abstract not provided.
Fabrication and Control of III-Nitride Nanowire Lasers
Abstract not provided.
Deterministically placed quantum dots for quantum nanophotonics
International Conference on Transparent Optical Networks
The ability to achieve deterministic placement of semiconductor quantum dots (QDs) opens up interesting possibilities for nanophotonic devices. By incorporating these QDs within microcavities, light-matter interaction can be tailored and enhanced, enabling phenomenon such as spontaneous emission enhancement, low threshold lasing, single photon emission and strong-coupling. The quality of these phenomena relies on the distribution of emission wavelengths of the emitter dipoles and the strength of their coupling to internal fields of the cavity. Therefore size-controlled fabrication of QDs and their deterministic placement become quite important. In this work we will describe a photoelectrochemical-based etching of III-nitride materials to achieve QDs with uniform emission wavelength. By patterning using electron beam lithography to create a nanopost structure in an epitaxially grown III-nitride based quantum well structure, we will show potential for deterministic placement. The photoluminescence response from the nanopost structure after photoelectrochemical etching reveals sharp lines indicative of quantum dot formation.
Chemical Interference of Quantum Size Controlled Photoelectrochemical Fabrication
Abstract not provided.
Nanophotonic Structures for Quantum Light Sources
Abstract not provided.
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