Dimitars Jevtics

We report a technique for scalable electro-optical on-chip addressing of semiconductor nanowire emitters via transfer-printed micro-LEDs. Thus driven individual waveguide-coupled nanowires demonstrate small-signal modulation in the 10’s MHz range at room-temperature. The integration of micro-LEDs with nanowire emitters on a chip provides localized scalable excitation without the need for external optics. This method therefore opens new routes for the realization of programmable high-density nanowire networks.

Transfer printing is employed to demonstrate the integration of gallium nitride (GaN)-based distributed Bragg reflectors (DBR) with 100 μm lateral dimensions and reflectance of 90% in various formats. Mesoporous GaN DBRs are utilized as basic building blocks to fabricate more complex photonic devices directly on Silicon (Si) and glass receiving substrates. Multi-mode optical resonant cavities centered at 450 nm on Si are thus formed by direct stacking of two mesoporous DBR membranes. Furthermore, active devices are also demonstrated by combining mesoporous DBR with GaN-based light-emitting diodes membranes of similar dimensions, resulting in a Fabry–Perot-mediated emission with its main peak shifted by 14 nm compared to a reference device without DBR. Measured optical bandwidth of 136 MHz (−6 dB) in a small signal modulation scheme is also demonstrated from these devices.

A scalable excitation platform for nanophotonic emitters using individually addressable micro-LED-on-CMOS arrays is presented. Heterogeneous integration by transfer printing of semiconductor nanowires was used for the deterministic assembly of the infrared emitters embedded in polymer optical waveguides with a high yield and positional accuracy. Direct optical pumping of these emitters is demonstrated using micro-LED pixels as a source, with optical modulation (on-off keying) measured up to 150 MHz. A micro-LED-on-CMOS array of pump sources was employed to demonstrate individual control of multiple waveguide-coupled nanowire emitters in parallel, enabling future large-scale photonic integrated circuit applications.

A scalable excitation platform for nanophotonic emitters using individually addressable micro-LED-on-CMOS arrays is demonstrated for the first time. Heterogeneous integration by transfer-printing of semiconductor nanowires was used for the deterministic assembly of the infrared emitters embedded in polymer optical waveguides with high yield and positional accuracy. Direct optical pumping of these emitters is demonstrated using micro-LED pixels as source, with optical modulation (on-off keying) measured up to 150 MHz. A micro-LED-on-CMOS array of pump sources were employed to demonstrate individual control of multiple waveguide coupled nanowire emitters in parallel, paving the way for future large scale photonic integrated circuit applications.

We report on the fabrication and micro-transfer printing (µ-TP) of InGaAs/InP avalanche photodiodes (APDs) onto silicon substrates. A process flow was developed to suspend the devices using semiconductor tethers. The developed process reduces the number of fabrication steps required compared to methods based on the use of photoresist tethers. Furthermore, our process is compatible with devices that may be susceptible to damage induced by the photoresist removal process. APDs were characterised in linear mode operation both before suspension and after printing. Despite the additional fabrication steps required to suspend the APD membranes and the physical nature of the µ-TP process, the electrical characteristics of the devices were preserved. No degradation in the optical performance of the devices was measured. Our work represents the first demonstration of µ-TP of InGaAs/InP APDs onto silicon substrates. The results highlight the viability of µ-TP for effective heterogeneous integration of InGaAs/InP APDs with silicon photonic integrated circuits for optical and quantum communication and other light detection applications.

Individually addressable micro-LED-on-CMOS arrays are promising candidates for scalable on-chip excitation of micro- and nano-photonic emitters. Using this technology platform, frequency modulated excitation of waveguide-embedded nanowire devices was demonstrated at MHz rates.

Supraparticle (SP) microlasers fabricated by the self-assembly of colloidal nanocrystals have great potential as coherent optical sources for integrated photonics. However, their deterministic placement for integration with other photonic elements remains an unsolved challenge. In this work, we demonstrate the manipulation and printing of individual SP microlasers, laying the foundation for their use in more complex photonic integrated circuits. We fabricate CdS_xSe_1-x/ZnS colloidal quantum dot (CQD) SPs with diameters from 4 to 20 μm and Q-factors of approximately 300 via an oil-in-water self-assembly process. Under a subnanosecond-pulse optical excitation at 532 nm, the laser threshold is reached at an average number of excitons per CQD of 2.6, with modes oscillating between 625 and 655 nm. Microtransfer printing is used to pick up individual CQD SPs from an initial substrate and move them to a different one without affecting their capability for lasing. As a proof of concept, a CQD SP is printed on the side of an SU-8 waveguide, and its modes are successfully coupled to the waveguide.

This study investigates the luminescence efficiency of red-emitting quantum-dots in supraparticles, a new type of microscopic photonic source. We demonstrate that compound supraparticles, created by incorporating higher-bandgap quantum dots in their design, reduce energy transfer losses and increase quantum dot luminescence efficiency.

A continuous, single shot roller transfer printing process is presented for the large-scale hybrid integration of semiconductor devices. Transfer of a 320 × 240 pixel micro-LED array, representing >75,000 individual devices in a single shot with sub-micron relative position accuracy is demonstrated. The transfer printing process preserves the array geometry with pixel spatial location error less than 1 µm deviation from the as-designed layout. An automated sub-micron precision metrology system based on simple optical microscopy was developed to asses such large device populations and allow the assessment of yield.

The development of advanced optoelectronic systems requires the intimate integration of multiple, different photonic materials and device structures at micron scales. A number of approaches are being explored to address this pressing challenge. Here we focus on soft-stamp-based transfer printing in both planar and roll based formats, to achieve a widely applicable capability in heterogeneous integration with micron-scale accuracy. We illustrate the capabilities of our custom tools by two examples, the first focusing on planar printing of GaN microlenses onto diamond substrates and waveguide facets and the second focusing on continuous roll-based printing of GaN micro-LED pixels at quarter VGA resolution.