Alec M. Skipper

To realize practical quantum information processing systems with high fidelity, disparate materials and components must be integrated on a scalable, unified platform. Among these, III-V alloys with their widely tunable optical properties and advantageous transport properties are strong candidates for the generation, manipulation, and detection of qubit states. Here, we present selective area growth (SAG) of III-V semiconductors by molecular beam epitaxy (MBE) as a uniquely well-advantaged approach to overcome the limitations of heterogeneous and hybrid integration. We review the underlying mechanisms of SAG by MBE and notable recent advancements enabled by this technique. Then, we discuss III-V components that are of utmost importance for various quantum architectures including nanowires for hosting Majorana modes, quantum dots for both classical lasers and single-photon generation, nonlinear nanophotonics for the manipulation of light, and avalanche photodiodes for single photon counting. For each device architecture, we review recent advances in the performance of these components for quantum applications and identify key opportunities for SAG to be applied to realize scalable integrated systems.

We investigate the amorphous-to-crystalline transformation of antimony selenide (Sb2Se3) on UHV-prepared GaAs (001) substrates. In the bulk orthorhombic form, Sb2Se3 is a layered quasi-1D semiconductor with highly anisotropic properties of interest for optical and electronic devices. We find that an amorphous layer deposited by molecular beam epitaxy annealed at or above 230 °C yields a textured-epitaxial structure among some randomly oriented domains. The textured-epitaxial Sb2Se3 grains are oriented with the covalently bonded “1D axis” constrained in-plane to GaAs [110] and with multiple van der Waals (hk0) orientations out-of-plane. The same texture was achieved exclusively without randomly oriented grains using continuous-wave laser radiation, highlighting the use of thermal and optical methods to yield anisotropic crystalline Sb2Se3 films directly from the amorphous phase. Polarized reflectance and polarized microscopy confirm the unique state of in-plane birefringence in the crystallized thin film. Overall, we show that solid-phase heteroepitaxy provides additional pathways to the integration of low-symmetry chalcogenide semiconductors for demanding applications where the inherent anisotropy needs to be preserved.

Presents corrections to the author listings in the paper, “Quantum Dot DBR Lasers Monolithically Integrated on Silicon Photonics by In-Pocket Heteroepitaxy,” (Koscica, R., et al., 2025).

We prepare quasi-1D films of Sb ₂ Se ₃ on GaAs by molecular beam epitaxy. The aligned grains and anisotropic bonding hierarchy of the Sb ₂ Se ₃ unit cell together produce giant birefringence in the near-infrared.

The direct growth of III-V lasers on silicon has the potential to allow for low-cost production of silicon photonic integrated circuits on a 300 mm wafer-scale. However, coupling loss severely limits the performance in current implementations of direct growth processes due to the growth of undesirable polycrystalline material on silicon dioxide sidewalls. In this work, we report the use of selective area molecular beam epitaxy growth to reduce the formation of this polycrystalline material during the growth process and improve the coupling efficiency. Furthermore, we demonstrate electrically pumped continuous wave lasers directly grown on foundry-fabricated silicon photonic integrated circuit wafers using this technique.

Monolithically integrated lasers on silicon photonics enable scalable, foundry-compatible production for data communications applications. However, material mismatches in heteroepitaxial systems and high coupling losses pose challenges for III-V integration on silicon. We combine three techniques: recessed silicon pockets for III-V growth, two-step heteroepitaxy using both MOCVD and MBE, and a polymer facet gap-fill approach to develop O-band InAs quantum dot lasers monolithically integrated on silicon photonics chiplets. Lasers coupled to silicon ring resonators and silicon nitride distributed Bragg reflectors (DBR) demonstrate single-mode lasing with side-mode suppression ratio up to 32 dB. Devices lase at temperatures up to 105 °C with an extrapolated operational lifetime of 6.2 years at 35 °C.

Analysis and mitigation of junction leakage currents are central to the engineering of vertical semiconductor diode structures. We have used scanning capacitance microscopy and conductive atomic force microscopy to characterize, with nanoscale spatial resolution, charge carrier distributions and local current distributions at the edges of mesa-etched and selective-area regrown vertical GaAs pn junction diodes grown by molecular-beam epitaxy. These studies indicate that wet etch-induced defect states are present on the etched surfaces of mesa structures, leading to increased local electrical conductivity that could contribute to sidewall leakage. For selective-area regrown structures, we observe an annular low-conductivity region in the vicinity of the GaAs–SiO2 interface at the edge of regrown pn junction structures that could act to suppress current flow at the edges of pn junction diodes fabricated from selective-area regrown material. Together, these studies provide new insights into the origin of sidewall leakage currents in mesa-etched GaAs pn junction diodes and their suppression in selective-area regrown devices.

We present the results of direct measurements of the effect of mechanically applied biaxial strain on Auger recombination rates in InGaAs quantum wells grown on InP. By mounting these structures on a flexible membrane, we applied strain mechanically rather than by changing the quantum well alloy fraction. Specifically, we employed time-resolved photoluminescence spectroscopy to probe the recombination dynamics in the degenerate carrier regime. From these measurements, we extract the non-degenerate cubic Auger coefficient C30. We found that applying 1.59% tensile biaxial strain increased the Auger C30 coefficient by 325% in one of our samples. These results support the hypothesis that the mechanical strain induced by heteroepitaxy plays a direct role in mitigating Auger recombination in InP-based telecommunication-range lasers.

Asymmetric molecular bonds possess a microscopic second-order nonlinear optical polarizability p(2). Crystals built from them possess a macroscopic second-order nonlinear optical susceptibility, χ(2), if their structure lacks centrosymmetry. χ(2) can be enhanced by introducing additional asymmetry at the meta-structural level. Here, we use a dipole matrix formalism to calculate χ(2) of asymmetric GaAs/AlGaAs coupled quantum well structures at telecommunication frequencies, for which interband (rather than previously considered intersubband) optical transitions govern optical nonlinearities. Using unit cell and envelope wavefunctions and considering all possible transitions between two bound electron and two bound hole states, we predict tenfold enhancement in χ(2) in previously underexplored ranges of quantum well asymmetry and coupling barrier thickness. This work paves the way toward enhanced, tailorable second-order optical nonlinearities for semiconductor digital alloy and superlattice structures.

2023 International Conference on Solid State Devices and Materials ,Quantum Dot Lasers on Silicon for Monolithic Photonic Integrated Circuits