Showing papers by "Thomas Fromherz published in 2017"
TL;DR: The experimental results demonstrate the great potential of the approach allowing CMOS-compatible parallel fabrication of arrays of spatially matched dot/cavity systems for group-IV-based data transfer or quantum optical systems in the telecom regime.
Abstract: Efficient coupling to integrated high-quality-factor cavities is crucial for the employment of germanium quantum dot (QD) emitters in future monolithic silicon-based optoelectronic platforms. We report on strongly enhanced emission from single Ge QDs into L3 photonic crystal resonator (PCR) modes based on precise positioning of these dots at the maximum of the respective mode field energy density. Perfect site control of Ge QDs grown on prepatterned silicon-on-insulator substrates was exploited to fabricate in one processing run almost 300 PCRs containing single QDs in systematically varying positions within the cavities. Extensive photoluminescence studies on this cavity chip enable a direct evaluation of the position-dependent coupling efficiency between single dots and selected cavity modes. The experimental results demonstrate the great potential of the approach allowing CMOS-compatible parallel fabrication of arrays of spatially matched dot/cavity systems for group-IV-based data transfer or quantum o...
44 citations
10 Apr 2017
TL;DR: In this article, high-Q/V photonic crystal cavities in thin silicon membranes, with resonances around 1.55 μm wavelength, have been realized with measured Q-factors in the 1 × 106 range.
Abstract: We report on the realization of high-Q/V photonic crystal cavities in thin silicon membranes, with resonances around 1.55 μm wavelength. The cavity designs are based on a recently proposed photonic crystal implementation of the Aubry-Andre-Harper bichromatic potential, defined from the superposition of two one-dimensional lattices with a non-integer ratio between their periodicity constants. In photonic crystal nanocavities, this confinement mechanism is such that optimized figures of merit can be straightforwardly achieved, in particular an ultra-high-Q factor and diffraction-limited mode volume. Several silicon membrane photonic crystal nanocavities have been realized with measured Q-factors in the 1 × 106 range, as evidenced by resonant scattering. The generality of the proposed designs and their easy implementation and scalability make these results particularly interesting for realizing highly performing photonic nanocavities on different material platforms and operational wavelengths.
39 citations
TL;DR: In this article, anisotropic biaxial stress was used to tune the built-in dipole moment of excitons confined in In(Ga)As quantum dots up to complete erasure of its magnitude and inversion of its sign.
Abstract: We show that anisotropic biaxial stress can be used to tune the
built-in dipole moment of excitons confined in In(Ga)As quantum
dots up to complete erasure of its magnitude and inversion of
its sign. We demonstrate that this phenomenon is due to
piezoelectricity. We present a model to calculate the applied
stress, taking advantage of the so-called piezotronic effect,
which produces significant changes in the current-voltage
characteristics of the strained diode-membranes containing the
quantum dots. Finally, self-consistent k.p calculations reveal
that the experimental findings can be only accounted for by the
nonlinear piezoelectric effect, whose importance in quantum dot
physics has been theoretically recognized although it has
proven difficult to single out experimentally.
25 citations
TL;DR: In this paper, the authors show that the room-temperature photoluminescence intensity from Ge ion-bombarded (GIB) epitaxial Ge on Si quantum dots (QD) can be improved by their vertical stacking.
Abstract: In this work, we show that the room-temperature photoluminescence intensity from Ge ion-bombarded (GIB) epitaxial Ge on Si quantum dots (QD) can be improved by their vertical stacking. We stress that the growth of GIB-QD multilayers is more demanding compared to all-crystalline epitaxial QDs, as a consequence of local amorphous regions within the GIB-QDs required during their genesis. We show that in spite of those amorphous regions, for accurately chosen growth temperatures of the Si spacer layers separating the GIB-QD layers, multiple GIB-QD layers can be stacked without detrimental break-down of epitaxial growth. Compared to a single GIB-QD layer, we observe a 650% increase in PL intensity for an eleven-layer GIB-QD stack, indicating that such multilayers are promising candidates as gain material for all-group-IV nano-photonic lasers.
18 citations
01 Jul 2017
TL;DR: The generality of the proposed designs and their easy implementation and scalability make these results particularly interesting for realizing highly performing photonic nanocavities on different material platforms and operational wavelengths.
Abstract: We report on the realization of high-Q/V silicon photonic crystal cavities with resonance wavelengths in the telecom window around 1.55 µm. The cavity designs are based on an effective Aubry-Andre-Harper bichromatic potential, defined by the superposition of two one-dimensional lattices with an incommensurate ratio between their periodicity constants. This peculiar confinement mechanism allows to achieve an ultra-high-Q factor and diffraction-limited mode volume. Several photonic crystal nanocavities in a silicon membrane geometry have been realized with measured Q-factors in the one million range, as determined by resonant scattering experiments. The generality of the proposed designs and their easy implementation and scalability make these results particularly interesting for realizing highly performing photonic nanocavities on different material platforms and operational wavelengths.