Daniel J. Ironside

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.

Optoelectronic devices in the mid-infrared have attracted significant interest due to numerous potential applications in communications and sensing. Molecular beam epitaxial (MBE) growth of highly doped InAs has emerged as a promising “designer metal” platform for the plasmonic enhancement of mid-infrared devices. However, while typical plasmonic materials can be patterned to engineer strong localized resonances, the lack of lateral control in conventional MBE growth makes it challenging to create similar structures compatible with monolithically grown plasmonic InAs. To this end, we report the growth of highly doped InAs plasmonic ridges for the localized resonant enhancement of mid-IR emitters and absorbers. Furthermore, we demonstrate a method for regaining a planar surface above plasmonic corrugations, creating a pathway to epitaxially integrate these structures into active devices that leverage conventional growth and fabrication techniques.

Photomixers at THz frequencies offer an attractive solution to fill the THz gap; however, conventional photomixer designs result in low output powers, on the order of microwatts, before thermal failure. We propose an alternative photomixer design capable of orders of magnitude enhancement of continuous-wave THz generation using a metamaterial approach. By forming a metal-semiconductor-metal (MSM) cavity through layering an ultrafast semiconductor material between subwavelength metal-dielectric gratings, tailored resonance can achieve ultrathin absorbing regions and efficient heat sinking. When mounted to a tunable E-patch antenna, gratings also act as vertically biased electrodes, further enhancing photoconductive gain by reducing the carrier path length to nanoscales. Thus, through these multiplicative enhancements, the metamaterial-enhanced photomixer is projected to generate THz powers in the milliwatt range and exceed the Manley-Rowe limit for frequencies less than 2 THz.

We demonstrate that plasmonic response can be tuned spectrally via the alloy composition of an epitaxial semimetallic film. Specifically, attenuated total reflectance studies show that the surface plasmon resonance of rare-earth monopnictide La_xLu_1–xAs alloy films can be tuned across the mid-IR, while lattice-matching to technologically important substrates. The electrical properties are a strong function of the composition, which, in turn, manifests as tunability of the optical properties. The ability to produce tunable (semi)metals that can be epitaxially integrated with III–V emitters and absorbers is expected to enable a new generation of novel nanophotonic device architectures and functionality.

We report the effect of growth interruptions on the structural and optical properties of InAs/InAlGaAs/InP quantum dots using molecular beam epitaxy. We find that the surface quantum dots experience an unintended ripening process during the sample cooling stage, which reshapes the uncapped InAs nanostructures. To prevent this, we performed a partial capping experiment to effectively inhibit structural reconfiguration of surface InAs nanostructures during the cooling stage, revealing that InAs nanostructures first form quantum dashes and then transform into quantum dots via a ripening process. Our result suggests that the appearance of buried InAs/InAlGaAs nanostructures can be easily misunderstood by surface analysis.