van Pj René Veldhoven

Ultra thin DVS-BCB adhesive bonding of III-V wafers dies and multiple dies to a patterned silicon-on-insulator substrate

Heterogeneous integration of III-V semiconductor materials on a silicon-on-insulator (SOI) platform has recently emerged as one of the most promising methods for the fabrication of active photonic devices in silicon photonics. For this integration, it is essential to have a reliable and robust bonding procedure, which also provides a uniform and ultra-thin bonding layer for an effective optical coupling between III-V active layers and SOI waveguides. A new process for bonding of III-V dies to processed silicon-on-insulator waveguide circuits using divinylsiloxane-bis-benzocyclobutene (DVS-BCB) was developed using a commercial wafer bonder. This “cold bonding” method significantly simplifies the bonding preparation for machine-based bonding both for die and wafer-scale bonding. High-quality bonding, with ultra-thin bonding layers (<50 nm) is demonstrated, which is suitable for the fabrication of heterogeneously integrated photonic devices, specifically hybrid III-V/Si lasers.

Record performance of electrical injection sub-wavelength metallic-cavity semiconductor lasers at room temperature

We demonstrate a continuous wave (CW) sub-wavelength metallic-cavity semiconductor laser with electrical injection at room temperature (RT). Our metal-cavity laser with a cavity volume of 0.67λ3 (λ = 1591 nm) shows a linewidth of 0.5 nm at RT, which corresponds to a Q-value of 3182 compared to 235 of the cavity Q, the highest Q under lasing condition for RT CW operation of any sub-wavelength metallic-cavity laser. Such record performance provides convincing evidences of the feasibility of RT CW sub-wavelength metallic-cavity lasers, thus opening a wide range of practical possibilities of novel nanophotonic devices based on metal-semiconductor structures.

Wavelength tuning of InAs quantum dots grown on InP (100) by chemical-beam epitaxy

We report on an effective way to continuously tune the emission wavelength of InAs quantum dots (QDs) grown on InP (100) by chemical-beam epitaxy. The InAs QD layer is embedded in a GaInAsP layer lattice matched to InP. With an ultrathin GaAs layer inserted between the InAs QD layer and the GaInAsP buffer, the peak wavelength from the InAs QDs can be continuously tuned from above 1.6 μm down to 1.5 μm at room temperature. The major role of the thin GaAs layer is to greatly suppress the As/P exchange during the deposition of InAs and subsequent growth interruption under arsenic flux, as well as to consume the segregated surface In layer floating on the GaInAsP buffer layer.

All-optical switching due to state filling in quantum dots

We report all-optical switching due to state filling in quantum dots (QDs) within a Mach–Zehnder interferometric switch (MZI). The MZI was fabricated using InGaAsP/InP waveguides containing a single layer of InAs/InP QDs. A 1530–1570 nm probe beam is switched by optical excitation of one MZI arm. By exciting below the InGaAsP band gap, we prove that the refractive index nonlinearity is entirely due to the QDs. The switching efficiency is 5 rad/(μW absorbed power), corresponding to a 6 fJ switching energy. Probe wavelength insensitivity was obtained using a broad size distribution of QDs.

Wavelength-tunable (1.55‐μm region) InAs quantum dots in InGaAsP∕InP (100) grown by metal-organic vapor-phase epitaxy

Growth of wavelength-tunable InAs quantum dots (QDs) embedded in a lattice-matched InGaAsP matrix on InP (100) substrates by metal-organic vapor-phase epitaxy is demonstrated. As∕P exchange plays an important role in determining QD size and emission wavelength. The As∕P exchange reaction is suppressed by decreasing the QD growth temperature and the V∕III flow ratio, reducing the QD size and emission wavelength. The As∕P exchange reaction and QD emission wavelength are then reproducibly controlled by the thickness of an ultrathin [zero to two monolayers (MLs)] GaAs interlayer underneath the QDs. An extended interruption after GaAs interlayer growth is essential to obtain well-defined InAs QDs. Submonolayer GaAs coverages result in a shape transition from QD to quantum dash at low V∕III flow ratio with a slightly shorter emission wavelength. Only the combination of reduced growth temperature and V∕III flow ratio with the insertion of GaAs interlayers above ML thicknesses allows wavelength tuning of QDs at r...

Electromechanical wavelength tuning of double-membrane photonic crystal cavities

We present a method for tuning the resonant wavelength of photonic crystal cavities (PCCs) around 1.55 μm. Large tuning of the PCC mode is enabled by electromechanically controlling the separation between two parallel InGaAsP membranes. A fabrication method to avoid sticking between the membranes is discussed. Reversible red/blueshifting of the symmetric/antisymmetric modes has been observed, which provides clear evidence of the electromechanical tuning, and a maximum shift of 10 nm with <6 V applied bias has been obtained.

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.

InAs/InP quantum dots emitting in the 1.55 μm wavelength region by inserting submonolayer GaP interlayers

We report on the growth of InAs quantum dots (QDs) in GaInAsP on InP (100) substrates by chemical-beam epitaxy, with emission wavelength in the 1.55μm region. Submonolayer coverage of GaP on the GaInAsP buffer before deposition of the InAs QDs results in most efficient suppression of As∕P exchange during InAs growth and subsequent growth interruption under arsenic flux. Continuous wavelength tuning from above 1.6 to below 1.5μm is thus achieved by varying the coverage of the GaP interlayer within the submonolayer range. Temperature dependent photoluminescence reveals distinct zero-dimensional carrier confinement and indicates that the InAs QDs are free of defects and dislocations.

Size-dependent exciton g factor in self-assembled InAs/InP quantum dots

We have studied the size dependence of the exciton g factor in self-assembled InAs/InP quantum dots. Photoluminescence measurements on a large ensemble of these dots indicate a multimodal height distribution. Cross-sectional scanning tunneling microscopy measurements have been performed and support the interpretation of the macrophotoluminescence spectra. More than 160 individual quantum dots have systematically been investigated by analyzing single dot magnetoluminescence between 1200 and 1600 nm. We demonstrate a strong dependence of the exciton g factor on the height and diameter of the quantum dots, which eventually gives rise to a sign change of the g factor. The observed correlation between exciton g factor and the size of the dots is in good agreement with calculations. Moreover, we find a size-dependent anisotropy splitting of the exciton emission in zero magnetic field.

Influence of an ultrathin GaAs interlayer on the structural properties of InAs/InGaAsP/InP (001) quantum dots investigated by cross-sectional scanning tunneling microscopy

Cross-sectional scanning tunneling microscopy is used to study at the atomic scale how the structural properties of InAs∕InGaAsP∕InP quantum dots (QDs) are modified when an ultrathin (0–1.5 ML) GaAs interlayer is inserted underneath the QDs. Deposition of the GaAs interlayer suppresses the influence of the As∕P exchange reaction on QD formation and leads to a planarized QD growth surface. A shape transition from quantum dashes, which are strongly dissolved during capping, to well defined QDs takes place when increasing the GaAs interlayer thickness between 0 and 1.0 ML. Moreover, the GaAs interlayer allows the control of the As∕P exchange reaction, reducing the QD height for increased GaAs thicknesses above 1.0 ML, and decreases the QD composition intermixing, producing almost pure InAs QDs.