This project has succeeded in delivering many of the key objectives related to the design, materials development, integration and exploration of functional classical and non-classical on-chip light sources using quantum NW-heterostructures.
One essential objective was the investigation of ultrasmall nanowire (NW) lasers at near-infrared and mid-infrared wavelengths (including the telecom-band wavelength range) and their coupling performance to underlying photonic circuitries. To this end, suitable III-V NW materials were developed with optimized resonator structures in the single-NW limit that host natural Fabry-Perot cavities and which can be deterministically placed on technologically relevant silicon photonic platform. Primarily focusing on the GaAs NW-material platform, which is technologically highly relevant but faces substantial materials challenges, NW-lasers were successfully realized both in the intrinsic bulk form (GaAs, InAs NW-lasers) as well as by novel ternary (GaAsSb) and more complex core-multishell (NW-quantum well type) gain media. Substantial work was aimed at realizing low threshold lasing performance over wide ranges of operation temperature (including room temperature) at Si-transparent wavelengths (e.g. telecom O-band, 1.3 µm) as well as at mid-infrared wavelengths (~2.5-3 µm). Such unique vertical-cavity nanolasers were also examined with respect to their light coupling efficiency to Si photonic circuits. Under optimized geometries and proper mirror design, large coupling efficiencies of >50% were achieved and first vertically, on-chip coupled NW-lasers at telecom-bands were demonstrated.
Important achievements were also made towards the realization of electrically driven III-V NW sources, which present an outstanding technological milestone. In this regard, coaxially p-i-n doped NW laser diode structures were established, where some of the challenging doping characteristics were solved and functional heterostructures established. Importantly, optical pumping was demonstrated on fully p-i-n doped NW-laser diode structures as-grown on Si platform with lasing thresholds that are on par with those reported for undoped NW-laser structures. While no electrically injected device could be demonstrated within the duration of this project, the research performed and insights gained along this direction hold great promises for successful outcomes in the near term.
For non-classical NW-based light sources that address new types of quantum photonic integrated circuits (QPIC), a fundamentally novel architecture was realized that embeds single quantum dots (QD) as ideal sources for high-brightness single photons. Such deterministic sources are a key ingredient for quantum technological applications in secure data communication and distributed quantum computing. First, through numerical simulations a vertical-cavity architecture was designed for maximizing light coupling and propagation of single photons into a silicon-on-insulator (SOI)-based QPIC. By placing the QD emitter close to the SOI-based WG, peak power coupling efficiencies of up to > 80% were realized. With these guidelines, Si waveguides on SOI platform were demonstrated experimentally and the monolithic growth of NW cavities with embedded quantum dot (QD) emitters pursued. Best-practice NW-QD materials were developed using GaAs(Sb)-InGaAs materials, where numerous studies have shown their excellent axial growth characteristics and distinct emission characteristics of the embedded, deterministic emitter. This sources provide a straightforward route to realize a scalable platform for on-chip quantum light sources integrated on next-generation QPICs.
The results of this action have been successfully disseminated within the research community, including a large number (>20) of peer-reviewed publications and many presentations at international conferences.
