Enhanced light emission of germanium light-emitting-diode on 150 mm germanium-on-insulator (GOI).

Germanium-on-insulator (GOI) has emerged as a novel platform for Ge-based electronic and photonic applications. Discrete photonic devices, such as waveguides, photodetectors, modulators, and optical pumping lasers, have been successfully demonstrated on this platform. However, there is almost no report on the electrically injected Ge light source on the GOI platform. In this study, we present the first fabrication of vertical Ge p-i-n light-emitting diodes (LEDs) on a 150 mm GOI substrate. The high-quality Ge LED on a 150-mm diameter GOI substrate was fabricated via direct wafer bonding followed by ion implantations. As a tensile strain of 0.19% has been introduced during the GOI fabrication process resulting from the thermal mismatch, the LED devices exhibit a dominant direct bandgap transition peak near 0.785 eV (∼1580 nm) at room temperature. In sharp contrast to conventional III-V LEDs, we found that the electroluminescence (EL)/photoluminescence (PL) spectra show enhanced intensities as the temperature is raised from 300 to 450 K as a consequence of the higher occupation of the direct bandgap. The maximum enhancement in EL intensity is a factor of 140% near 1635 nm due to the improved optical confinement offered by the bottom insulator layer. This work potentially broadens the GOI's functional variety for applications in near-infrared sensing, electronics, and photonics.

Ge-on-insulator lateral p-i-n waveguide photodetectors for optical communication.

We report high-performance lateral p-i-n Ge waveguide photodetectors (WGPDs) on a Ge-on-insulator (GOI) platform that could be integrated with electronic-photonic integrated circuits (EPICs) for communication applications. The high-quality Ge layer affords a low absolute dark current. A tensile strain of 0.144% in the Ge active layers narrows the direct bandgap to enable efficient photodetection over the entire range of C- and L-bands. The low-index insulator layer enhances optical confinement, resulting in a good optical responsivity. These results demonstrate the feasibility of planar Ge WGPDs for monolithic GOI-based EPICs.

Low-threshold optically pumped lasing in highly strained germanium nanowires.

The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system. Here we demonstrate a low-threshold, compact group IV laser that employs a germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently overcome optical losses at 83 K, thus allowing the observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm-2. Our demonstration opens new possibilities for group IV lasers for photonic-integrated circuits.

MoS2 nanoflower-decorated reduced graphene oxide paper for high-performance hydrogen evolution reaction.

A facile, one-pot solvothermal method is developed to synthesize MoS2 nanoflowers (MoS2NFs) coated on reduced graphene oxide (rGO) paper. The resulting MoS2NF/rGO paper serves as a freestanding, flexible and durable working electrode for hydrogen evolution reaction (HER), exhibiting an overpotential lowered to -0.19 V with a Tafel slope of ∼95 mV per decade.

Solution-phase epitaxial growth of noble metal nanostructures on dispersible single-layer molybdenum disulfide nanosheets.

Compared with the conventional deposition techniques used for the epitaxial growth of metallic structures on a bulk substrate, wet-chemical synthesis based on the dispersible template offers several advantages, including relatively low cost, high throughput, and the capability to prepare metal nanostructures with controllable size and morphology. Here we demonstrate that the solution-processable two-dimensional MoS(2) nanosheet can be used to direct the epitaxial growth of Pd, Pt and Ag nanostructures at ambient conditions. These nanostructures show the major (111) and (101) orientations on the MoS(2)(001) surface. Importantly, the Pt-MoS(2) hybrid nanomaterials exhibit much higher electrocatalytic activity towards the hydrogen evolution reaction compared with the commercial Pt catalysts with the same Pt loading. We believe that nanosheet-templated epitaxial growth of nanostructures via wet-chemical reaction is a promising strategy towards the facile and high-yield production of novel functional materials.