Matthew F. Doty
University of Delaware
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Publication
Featured researches published by Matthew F. Doty.
Applied Physics Letters | 2006
Allan S. Bracker; Michael Scheibner; Matthew F. Doty; Eric Stinaff; I. V. Ponomarev; J. C. Kim; L. J. Whitman; T. L. Reinecke; D. Gammon
Most self-assembled quantum dot molecules are intrinsically asymmetric with inequivalent dots resulting from imperfect control of crystal growth. The authors have grown vertically aligned pairs of InAs∕GaAs quantum dots by molecular beam epitaxy, introducing intentional asymmetry that limits the influence of intrinsic growth fluctuations and allows selective tunneling of electrons or holes. They present a systemic investigation of tunneling energies over a wide range of interdot barrier thickness. The concepts discussed here provide an important tool for the systematic design and characterization of more complicated quantum dot nanostructures.
ACS Nano | 2011
Fan Xu; Xin Ma; Chelsea R. Haughn; Jamie Benavides; Matthew F. Doty; Sylvain G. Cloutier
Benzenedithiol (BDT) and ethanedithiol (EDT) ligand-exchange treatments can be used to cross-link colloidal PbS quantum dots into nanocrystalline film structures with distinct optoelectronic properties. Such structures can provide a unique platform to study the energy transfer between layers of quantum dots with different sizes. In this report, efficient exciton funneling and recycling of surface state-bound excitons is observed in cascaded PbS quantum dot-based multilayered superstructures, where the excitons transfer from the larger band gap or donor layers to the smallest band gap or acceptor layers. In this system, both the BDT- and EDT-treated cascaded structures exhibit dramatically enhanced photoluminescence from the acceptor layers. As we show, the energy transfer mechanisms involved and their efficiencies are significantly different depending on the ligand-exchange treatment. In the future, we believe these efficient exciton recycling and funneling mechanisms could be used to improve significantly the photocurrent, charge-transport, and conversion efficiencies in low-cost nanocrystalline and hybrid solar cells and the emission efficiencies in hybrid light-emitting devices.
Physical Review Letters | 2005
Morgan E. Ware; Eric Stinaff; D. Gammon; Matthew F. Doty; Allan S. Bracker; D. Gershoni; V. L. Korenev; Stefan C. Badescu; Yuli Lyanda-Geller; T. L. Reinecke
We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.
Physical Review Letters | 2006
Matthew F. Doty; Michael Scheibner; I. V. Ponomarev; Eric Stinaff; Allan S. Bracker; V. L. Korenev; T. L. Reinecke; D. Gammon
We present a magnetophotoluminescence study of individual vertically stacked InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied electric field tunes the relative energies of the two dots, we observe a strong resonant increase or decrease in the g factors of different spin states that have molecular wave functions distributed over both quantum dots. We propose a phenomenological model for the change in g factor based on resonant changes in the amplitude of the wave function in the barrier due to the formation of bonding and antibonding orbitals.
Physical Review B | 2007
Michael Scheibner; Matthew F. Doty; I. V. Ponomarev; Allan S. Bracker; Eric Stinaff; V. L. Korenev; T. L. Reinecke; D. Gammon
The interaction between spins in coupled quantum dots is revealed in distinct fine structure patterns in the measured optical spectra of
Journal of Physics D | 2012
Musa Mutlu Can; S. Ismat Shah; Matthew F. Doty; Chelsea R. Haughn; Tezer Fırat
\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}
Applied Physics Letters | 2014
Diane G. Sellers; Stephen Polly; Seth M. Hubbard; Matthew F. Doty
double quantum dot molecules containing zero, one, or two excess holes. The fine structure is explained well in terms of a uniquely molecular interplay of spin-exchange interactions, Pauli exclusion, and orbital tunneling. This knowledge is critical for converting quantum dot molecule tunneling into a means of optically coupling not just orbitals but also spins.
Materials | 2015
Fan Xu; Luis Felipe Gerlein; Xin Ma; Chelsea R. Haughn; Matthew F. Doty; Sylvain G. Cloutier
We show that the deposition of ZnO films under varying oxygen partial pressure and annealing conditions allows for the controllable formation of specific defects. Using x-ray diffraction and photoluminescence, we characterize the defects formed and show that these defects are responsible for changes in film carrier density, carrier type, sheet resistivity and mobility.
Physical Review Letters | 2007
Michael Scheibner; I. V. Ponomarev; Eric Stinaff; Matthew F. Doty; A. S. Bracker; C. S. Hellberg; T. L. Reinecke; D. Gammon
Intermediate band solar cells (IBSCs) are third-generation photovoltaic (PV) devices that can harvest sub-bandgap photons normally not absorbed in a single-junction solar cell. Despite the large increase in total solar energy conversion efficiency predicted for IBSC devices, substantial challenges remain to realizing these efficiency gains in practical devices. We evaluate carrier escape mechanisms in an InAs/GaAs quantum dot intermediate band p-i-n junction PV device using photocurrent measurements under sub-bandgap illumination. We show that sub-bandgap photons generate photocurrent through a two-photon absorption process, but that carrier trapping and retrapping limit the overall photocurrent. The results identify a key obstacle that must be overcome in order to realize intermediate band devices that outperform single junction photovoltaic cells.
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena | 2011
Laura E. Cassels; Trevor E. Buehl; Peter G. Burke; Chris J. Palmstrøm; A. C. Gossard; Gilles Pernot; Ali Shakouri; Chelsea R. Haughn; Matthew F. Doty; Joshua M. O. Zide
The engineering of quantum dot solids with low defect concentrations and efficient carrier transport through a ligand strategy is crucial to achieve efficient quantum dot (QD) optoelectronic devices. Here, we study the consequences of various surface ligand treatments on the light emission properties of PbS quantum dot films using 1,3-benzenedithiol (1,3-BDT), 1,2-ethanedithiol (EDT), mercaptocarboxylic acids (MPA) and ammonium sulfide ((NH4)2S). We first investigate the influence of different ligand treatments on the inter-dot separation, which mainly determines the conductivity of the QD films. Then, through a combination of photoluminescence and transient photoluminescence characterization, we demonstrate that the radiative and non-radiative recombination mechanisms in the quantum dot films depend critically on the length and chemical structure of the surface ligands.