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Carrier leakage in Ge/Si core-shell nanocrystals for lasers: Core size and strain effects

Proceedings of SPIE - The International Society for Optical Engineering

Neupane, Mahesh R.; Rahman, Rajib R.; Lake, Roger K.

The electronic structure and optical properties of Ge-core/Si-shell nanocrystal or quantum dot (QD) are investigated using the atomistic tight binding method as implemented in NEMO3D. The thermionic lifetime that governs the hole leakage mechanism in the Ge/Si QD based laser, as a function of the Ge core size and strain, is also calculated by capturing the bound and extended eigenstates, well below the band edges. We also analyzed the effect of core size and strain on optical properties such as transition energies and transition rates between electron and hole states. Finally, a quantitative and qualitative analysis of the leakage current due to the hole leakage through the Ge-core/Si-shell QD laser, at different temperatures and Ge core sizes, is presented. © 2011 SPIE.

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TYPE Conference YEAR 2011
ScopusOSTI

Excited states and valley effects in a negatively charged impurity in a silicon FinFET

Rahman, Rajib R.; Muller, Richard P.; Carroll, Malcolm

The observation and characterization of a single atom system in silicon is a significant landmark in half a century of device miniaturization, and presents an important new laboratory for fundamental quantum and atomic physics. We compare with multi-million atom tight binding (TB) calculations the measurements of the spectrum of a single two-electron (2e) atom system in silicon - a negatively charged (D-) gated Arsenic donor in a FinFET. The TB method captures accurate single electron eigenstates of the device taking into account device geometry, donor potentials, applied fields, interfaces, and the full host bandstructure. In a previous work, the depths and fields of As donors in six device samples were established through excited state spectroscopy of the D0 electron and comparison with TB calculations. Using self-consistent field (SCF) TB, we computed the charging energies of the D- electron for the same six device samples, and found good agreement with the measurements. Although a bulk donor has only a bound singlet ground state and a charging energy of about 40 meV, calculations show that a gated donor near an interface can have a reduced charging energy and bound excited states in the D- spectrum. Measurements indeed reveal reduced charging energies and bound 2e excited states, at least one of which is a triplet. The calculations also show the influence of the host valley physics in the two-electron spectrum of the donor.

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TYPE Conference YEAR 2010
OSTI

Spectroscopy and capacitance measurements of tunneling resonances in an Sb-implanted point contact

Bishop, Nathaniel B.; Stevens, Jeffrey S.; Childs, Kenton D.; Ohlhausen, J.A.; Lilly, Michael L.; Carroll, Malcolm; Young, Ralph W.; Bielejec, Edward S.; Ten Eyck, Gregory A.; Wendt, J.R.; Rahman, Rajib R.; Grubbs, Robert K.

We fabricated a split-gate defined point contact in a double gate enhancement mode Si-MOS device, and implanted Sb donor atoms using a self-aligned process. E-beam lithography in combination with a timed implant gives us excellent control over the placement of dopant atoms, and acts as a stepping stone to focused ion beam implantation of single donors. Our approach allows us considerable latitude in experimental design in-situ. We have identified two resonance conditions in the point contact conductance as a function of split gate voltage. Using tunneling spectroscopy, we probed their electronic structure as a function of temperature and magnetic field. We also determine the capacitive coupling between the resonant feature and several gates. Comparison between experimental values and extensive quasi-classical simulations constrain the location and energy of the resonant level. We discuss our results and how they may apply to resonant tunneling through a single donor.

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TYPE Conference YEAR 2010
OSTI
23 Results
23 Results