Graphene/III-V Quantum Dot Mixed-Dimensional Heterostructure for Enhanced Radiative Recombinations via Hole Carrier Transfer.

Fabrication of high quantum efficiency nanoscale device is challenging due to increased carrier loss at surface. Low dimensional materials such 0D quantum dots and 2D materials have been widely studied to mitigate the loss. Here, we demonstrate a strong photoluminescence enhancement from graphene/III-V quantum dot mixed-dimensional heterostructures. The distance between graphene and quantum dots in the 2D/0D hybrid structure determines the degree of radiative carrier recombination enhancement from 80% to 800% compared to the quantum dot only structure. Time-resolved photoluminescence decay also shows increased carrier lifetimes when the distance decreases from 50 to 10 nm. We propose that the optical enhancement is due to energy band bending and hole carrier transfer, which repair the imbalance of electron and hole carrier densities in quantum dots. This 2D graphene/0D quantum dot heterostructure shows promise for high performance nanoscale optoelectronic devices.

High concentration bolometric system with single-walled carbon nanotubes (SWCNT) absorber.

We demonstrate that a planar single-walled carbon nanotube (SWCNT) film bolometer can exhibit enhanced thermal and optical properties. The SWCNT film were ink-printed on an oxidized silicon substrate between two pointed-tip Au electrodes across a gap of approximately 10 µm. We obtained a bolometer figure-of-merit temperature coefficient of resistance of greater than -3.0% at room temperature. An optical response of 1000 V W-1 was obtained from a 786 nm laser with an output power of 5 mW. The corresponding thermal time constant of 1.8 ms was estimated through the optical response by modulating the laser over a frequency range of 1 Hz-1 kHz. The optical noise equivalent power and optical detectivity of [Formula: see text] and [Formula: see text] respectively, were estimated from the responsivity, the spectral density, and area of the cell of the absorber, 4.9 × 10-4 cm2. We attribute the exceptional performance of the SWCNT microbolometer to the film nature of the absorber and to the high concentration of the incident electromagnetic radiation and localized heating between the tips of the electrode.

Reduction of GaAs Buffer Thickness and Its Impact on Epitaxially Integrated III-V Quantum Dot Lasers on a Si Substrate.

Monolithic integration of III-V quantum dot (QD) lasers onto a Si substrate is a scalable and reliable approach for obtaining highly efficient light sources for Si photonics. Recently, a combination of optimized GaAs buffers and QD gain materials resulted in monolithically integrated butt-coupled lasers on Si. However, the use of thick GaAs buffers up to 3 µm not only hinders accurate vertical alignment to the Si optical waveguide but also imposes considerable growth costs and time constraints. Here, for the first time, we demonstrate InAs QD lasers epitaxially grown on a 700 nm thick GaAs/Si template, which is approximately four times thinner than the conventional III-V buffers on Si. The optimized 700 nm GaAs buffer yields a remarkably smooth surface and low threading dislocation density of 4 × 108 cm-2, which is sufficient for QD laser growth. The InAs QD lasers fabricated on these ultrathin templates still lase at room temperature with a threshold current density of 661 A/cm2 and a characteristic temperature of 50 K. We believe that these results are important for the monolithically integrated III-V QD lasers for Si photonics applications.