Mid-infrared Imaging Using Strain-Relaxed Ge1-xSnx Alloys Grown on 20 nm Ge Nanowires

Germanium-tin (Ge1-xSnx) semiconductors are a front-runner platform for compact mid-infrared devices due to their tunable narrow bandgap and compatibility with silicon processing. However, their large lattice parameter has been a major hurdle, limiting the quality of epitaxial layers grown on silicon or germanium substrates. Herein, we demonstrate that 20 nm Ge nanowires (NWs) act as effective compliant substrates to grow extended defect-free Ge1-xSnx alloys with a composition uniformity over several micrometers along the NW growth axis without significant buildup of the compressive strain. Ge/Ge1-xSnx core/shell NWs with Sn content spanning the 6-18 at. % range are achieved and processed into photoconductors exhibiting a high signal-to-noise ratio at room temperature with a cutoff wavelength in the 2.0-3.9 μm range. The processed NW devices are integrated in an uncooled imaging setup enabling the acquisition of high-quality images under both broadband and laser illuminations at 1550 and 2330 nm without the lock-in amplifier technique.

Ultra-sensitive tandem colloidal quantum-dot photodetectors

The solution-processed PbSe colloidal quantum-dot (CQD) infrared photodetector with tandem architecture is proposed to address the high dark current issue. The electrical transport mechanism in tandem has been fundamentally changed in which the recombination of carriers at an intermediate layer becomes dominant rather than carriers hopping between nearest neighbors in CQD materials. As a result, the tandem photodetector exhibits ultra-high detectivities of 4.7 × 10(13) Jones and 8.1 × 10(13) Jones under 34 μW cm(-2) illumination at 1100 nm, at 275 K and 100 K, respectively.

Monolithic integration of nitride light emitting diodes and photodetectors for bi-directional optical communication

Design and fabrication of monolithically integrated III-nitride visible light-emitting-diodes (LEDs) and ultraviolet Schottky barrier-photodetectors (SB-PDs) have been proposed and demonstrated. Responsivity up to 0.2  AW(-1) at 365 nm for GaN SB-PDs has been achieved. It is shown that those UV SB-PDs were capable of sensitive UV light detection down to 7.16×10(-4)  W/cm2 at 365 nm, whereas simultaneous operation of on-chip blue LEDs has produced negligible crosstalk at practical illumination brightness. Monolithically integrated LEDs and SB-PDs can function as transmitters to emit visible light signals, and as receivers to analyze incoming UV signals, respectively; this offers the potential of using such devices for bi-directional optical wireless communication applications.