Aaron Hryciw

Atomic Layer Deposition of Lead Sulfide Quantum Dots on Nanowire Surfaces

Quantum dots provide unique advantages in the design of novel optoelectronic devices owing to the ability to tune their properties as a function of size. Here we demonstrate a new technique for fabrication of quantum dots during the nucleation stage of atomic layer deposition (ALD) of PbS. Islands with sub-10 nm diameters were observed during the initial ALD cycles by transmission electron microscopy, and in situ observations of the coalescence and sublimation behavior of these islands show the possibility of further modifying the size and density of dots by annealing. The ALD process can be used to cover high-aspect-ratio nanostructures, as demonstrated by the uniform coating of a Si nanowire array with a single layer of PbS quantum dots. Photoluminescence measurements on the quantum dot/nanowire composites show a blue shift when the number of ALD cycles is decreased, suggesting a route to fabricate unique three-dimensional nanostructured devices such as solar cells.

Plasmonics: Electrifying plasmonics on silicon

The realization of electrical sources of surface plasmon polaritons using complementary metal oxide semiconductor technology is a significant step towards silicon-compatible nanoscale photonic devices.

Solving dielectric and plasmonic waveguide dispersion relations on a pocket calculator.

We present a robust iterative technique for solving complex transcendental dispersion equations routinely encountered in integrated optics. Our method especially befits the multilayer dielectric and plasmonic waveguides forming the basis structures for a host of contemporary nanophotonic devices. The solution algorithm ports seamlessly from the real to the complex domain--i.e., no extra complexity results when dealing with leaky structures or those with material/metal loss. Unlike several existing numerical approaches, our algorithm exhibits markedly-reduced sensitivity to the initial guess and allows for straightforward implementation on a pocket calculator.

Plasmon-enhanced emission from optically-doped MOS light sources

We evaluate the spontaneous emission rate (Purcell) enhancement for optically-doped metal-dielectric-semiconductor light-emitting structures by considering the behavior of a semiclassical oscillating point dipole placed within the dielectric layer. For a Ag-SiO(2)-Si structure containing emitters at the center of a 20-nm-thick SiO(2) layer, spontaneous emission rate enhancements of 40 to 60 can be reached in the wavelength range of 600 to 1800 nm, far away from the surface plasmon resonance; similar enhancements are also possible if Al is used instead of Ag. For dipoles contained in the thin oxide layer of a Ag-SiO(2)-Si-SiO(2) structure, the emission exhibits strong preferential coupling to a single well-defined Si waveguide mode. This work suggests a means of designing a new class of power-efficient, high-modulation-speed, CMOS-compatible optical sources that take full advantage of the excellent electrical properties and plasmon-enhanced op cal properties afforded by MOS devices.

Energy transfer in nanowire solar cells with photon-harvesting shells

The concept of a nanowire solar cell with photon-harvesting shells is presented. In this architecture, organic molecules which absorb strongly in the near infrared where silicon absorbs weakly are coupled to silicon nanowires (SiNWs). This enables an array of 7-μm-long nanowires with a diameter of 50 nm to absorb over 85% of the photons above the bandgap of silicon. The organic molecules are bonded to the surface of the SiNWs forming a thin shell. They absorb the low-energy photons and subsequently transfer the energy to the SiNWs via Forster resonant energy transfer, creating free electrons and holes within the SiNWs. The carriers are then separated at a radial p-n junction in a nanowire and extracted at the respective electrodes. The shortness of the nanowires is expected to lower the dark current due to the decrease in p-n junction surface area, which scales linearly with wire length. The theoretical power conversion efficiency is 15%. To demonstrate this concept, we measure a 60% increase in photocurr...

Thermo-optic tuning of erbium-doped amorphous silicon nitride microdisk resonators

We demonstrate a technique to yield a direct and sensitive measurement of the thermo-optic coefficient (TOC) for light-emitting materials in optical microdisk resonators. Using photoluminescence from erbium-doped amorphous silicon nitride (a-SiNx:Er) as an example, we show how the TOC can be extracted from thermally induced shifts in the resonant microdisk modes. For the highest-performance a-SiNx:Er material composition, we find a TOC at 1.54u2002μm of ∼3×10−5u2002K−1 in the 300–500 K range. Additionally, our work demonstrates a convenient all-optical spectroscopic technique for sensitive temperature measurements, with a resolution of ∼30u2002mK in this temperature range.

Reversing the temperature dependence of the sensitized Er3+ luminescence intensity

The temperature-induced quenching of the Er3+ luminescence is a significant problem in silicon-based materials systems ultimately designed for room-temperature applications. Here, we show that amorphous silicon-rich oxide, moderately annealed in order to avoid growth of Si nanocrystals, exhibits a reversed temperature dependence in which the integrated Er3+ luminescence increases in intensity upon heating from 77 up to 300 K. This behavior is attributed to a unique spectrum of interacting defects that efficiently sensitize the Er3+ levels, even in the absence of nanocrystals. The effect could have ramifications in fiber-optic emitters or amplifiers to be operated at noncryogenic temperatures.