van Fwm Frank Otten

Stacking and polarization control of wavelength-tunable (1.55 μm region) InAs / InGaAsP / InP (100) quantum dots

Stacking and polarization control of wavelength-tunable InAs quantum dots (QDs) embedded in lattice-matched InGaAsP on InP (100) grown by metalorganic vapor-phase epitaxy is demonstrated. Wavelength control over the 1.55μm region at room temperature is achieved by inserting ultrathin GaAs interlayers underneath the QDs and adjusting the amount of InAs. For widely stacked QDs with a 40nm separation layer, the linear dependence of the emission wavelength on the GaAs interlayer thickness coincides with that of single QD layers revealing the reproduction of identical QD layers. For closely stacked QDs with 4nm separation layer, the emission wavelength as a function of the GaAs interlayer thickness is systematically redshifted and the linewidth is reduced indicating vertical electronic coupling which is proven by the linear polarization of the cleaved-side luminescence changing from in-plane to isotropic.

Formation of linear InAs quantum dot arrays on InGaAsP/InP (100) by self-organized anisotropic strain engineering and their optical properties

The formation of linear InAs quantum dot (QD) arrays based on self-organized anisotropic strain engineering of an InGaAsP∕InP (100) superlattice (SL) template in chemical beam epitaxy is demonstrated, and the optimized growth window is determined. InAs QD formation, thin InGaAsP capping, annealing, InGaAsP overgrowth, and stacking in SL template formation produce wirelike InAs structures along [001] due to anisotropic surface migration and lateral and vertical strain correlations. InAs QD ordering is governed by the corresponding lateral strain field modulation on the SL template surface. Careful optimization of InGaAsP cap layer thickness, annealing temperature, InAs amount and growth rate, and number of SL periods results in straight and well-separated InAs QD arrays. The InAs QD arrays exhibit excellent photoluminescence (PL) emission up to room temperature which is tuned into the 1.55μm telecommunications wavelength region through the insertion of ultrathin GaAs interlayers. Temperature dependent PL m...

Electromechanical tuning of vertically-coupled photonic crystal nanobeams

We present the design, the fabrication and the characterization of a tunable one-dimensional (1D) photonic crystal cavity (PCC) etched on two vertically-coupled GaAs nanobeams. A novel fabrication method which prevents their adhesion under capillary forces is introduced. We discuss a design to increase the flexibility of the structure and we demonstrate a large reversible and controllable electromechanical wavelength tuning (> 15 nm) of the cavity modes.

Dynamically controlling the emission of single excitons in photonic crystal cavities

Single excitons in semiconductor microcavities represent a solid state and scalable platform for cavity quantum electrodynamics, potentially enabling an interface between flying (photon) and static (exciton) quantum bits in future quantum networks. While both single-photon emission and the strong coupling regime have been demonstrated, further progress has been hampered by the inability to control the coherent evolution of the cavity quantum electrodynamics system in real time, as needed to produce and harness charge–photon entanglement. Here using the ultrafast electrical tuning of the exciton energy in a photonic crystal diode, we demonstrate the dynamic control of the coupling of a single exciton to a photonic crystal cavity mode on a sub-nanosecond timescale, faster than the natural lifetime of the exciton. This opens the way to the control of single-photon waveforms, as needed for quantum interfaces, and to the real-time control of solid-state cavity quantum electrodynamics systems.

Wavelength controlled multilayer-stacked linear InAs quantum dot arrays on InGaAsP/InP(100) by self-organized anisotropic strain engineering : a self-ordered quantum dot crystal

Multilayer-stacked linear InAs quantum dot (QD) arrays are created on InAs/InGaAsP superlattice templates formed by self-organized anisotropic strain engineering on InP (100) substrates in chemical beam epitaxy. Stacking of the QD arrays with identical emission wavelength in the 1.55 μm region at room temperature is achieved through the insertion of ultrathin GaAs interlayers beneath the QDs with increasing interlayer thickness in successive layers. The increment in the GaAs interlayer thickness compensates the QD size/wavelength increase during strain correlated stacking. This is the demonstration of a three-dimensionally self-ordered QD crystal with fully controlled structural and optical properties.

Optical properties of stacked InGaAs sidewall quantum wires in InGaAsP∕InP

We report on the optical properties of threefold stacked InGaAs sidewall quantum wires (QWires) with quaternary InGaAsP barriers grown on shallow-patterned InP (311)A substrates by chemical beam epitaxy. Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent quantum wells (QWells) into the QWires at low temperature, thermally activated repopulation of the QWells at higher temperature, and negligible localization of carriers along the QWires. Strong broadening of power dependent PL indicates enhanced state filling in the QWires compared to that in the QWells. Clear linear polarization of the PL from the QWires confirms the lateral quantum confinement of carriers. These results demonstrate excellent optical quality of the sidewall QWire structures with room temperature PL peak wavelength at 1.55μm for applications in fiber-based optical telecommunication systems.

(In,Ga)As sidewall quantum wires on shallow-patterned InP (311)A

(In,Ga)As sidewall quantum wires (QWires) are realized by chemical beam epitaxy along [01-1] mesa stripes on shallow-patterned InP (311)A substrates. The QWires exhibit strong lateral carrier confinement due to larger thickness and In composition compared to the adjacent quantum wells, as determined by cross-sectional scanning-tunneling microscopy and microphotoluminescence (micro-PL) spectroscopy. The PL of the (In,Ga)As QWires with InP and quaternary (Ga,In)(As,P) barriers reveals narrow linewidth, high efficiency, and large lateral carrier confinement energies of 60–70meV. The QWires are stacked in growth direction with identical PL peak emission energy. The PL emission energy is not only controlled by the (In,Ga)As layer thickness but also by the patterned mesa height. Stacked (In,Ga)As QWires with quaternary barriers exhibit room temperature PL emission at 1.55μm in the technologically important wavelength region for telecommunication applications.

InAs/InGaAsP sidewall quantum dots on shallow-patterned InP (311)A

Highly strained InAs quantum dots (QDs) embedded in InGaAsP are formed at the fast-growing [01−1] mesa sidewall on shallow-patterned InP (311)A substrates by chemical beam epitaxy. Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent dashlike QDs in the planar areas to the larger sidewall QDs resulting in well-distinguishable emission around 80K. The large high-energy shift of the PL from the sidewall QDs as a function of excitation power density is ascribed to the screening of the internal piezoelectric field. The linear polarization of the PL from the sidewall QDs is reversed compared to that of the quantum dashes in the planar areas due to the more symmetric shape and possible nonuniform strain in the sidewall QDs.

Wavelength tuning of InAs∕InP quantum dots: Control of As∕P surface exchange reaction

Wavelength tuning of single and vertically stacked InAs quantum dot (QD) layers embedded in InGaAsP∕InP (100) grown by metal organic vapor-phase epitaxy is achieved by controlling the As∕P surface exchange reaction during InAs deposition. The As∕P exchange reaction is suppressed for decreased QD growth temperature and group V-III flow ratio, reducing the QD size and photoluminescence (PL) emission wavelength. The As∕P exchange reaction and QD PL wavelength are then reproducibly controlled by the thickness of an ultrathin (0–2 ML) GaAs interlayer underneath the QDs. Submonolayer GaAs coverages result in a shape transition from QDs to quantum dashes at low group V-III flow ratio. Temperature dependent PL measurements reveal excellent optical properties of the QDs up to room temperature with PL peak wavelengths in the technologically important 1.55μm region for telecom applications. Widely stacked QD layers are reproduced with identical PL emission to increase the active volume, while closely stacked QD laye...

Role of Surface Morphology for INAS Quantum Dot or Dash Formation on INGAASP/INP (100)

We investigate the formation of self-assembled InAs quantum structures on lattice-matched InGaAsP on InP (100) substrates grown by chemical beam epitaxy. The surface morphology of the InGaAsP buffer layer plays a key role for the formation of InAs quantum dots (QDs) or dashes (QDashes). QDash formation is always accompanied by a rough buffer layer surface. Growth conditions such as higher growth temperature, larger As flux, and compressive buffer layer strain promote the formation of QDs. However, once, the buffer layer has a rough morphology, QDashes always form during InAs deposition. On the other hand, well-shaped and symmetric QDs are reproducibly formed on smooth InGaAsP buffer layers for the same InAs growth conditions. Hence, not the growth conditions during InAs deposition, but rather the surface morphology of the buffer layer determines the formation of QDs or QDashes, which both exhibit high optical quality.