Low-cost and efficient all group-IV visible/shortwave infrared dual-band photodetector.

Low-cost broadband photodetectors (PDs) based on group-IV materials are highly demanded. Herein, a vertical all group-IV graphene-i-n (Gr-i-n) structure based on sputtering-grown undoped Ge0.92Sn0.08/Ge multiple quantum wells (MQWs) on n-Ge substrate was proposed to realize efficient visible/shortwave infrared (VIS/SWIR) dual-band photoresponse. Harnessing Gr-germanium tin (GeSn)/Ge MQWs van der Waals heterojunctions, an extended surface depletion region was established, facilitating separation and transportation of photogenerated carriers at VIS wavelengths. Consequently, remarkable VIS/SWIR dual-band response ranging from 400 to 2000 nm with a rapid response time of 23 µs was achieved. Compared to the PD without Gr, the external quantum efficiency at 420, 660, and 1520 nm was effectively enhanced by 10.2-, 5.2-, and 1.2-fold, reaching 40, 42, and 50%, respectively. This research paves the way for the advancement of all group-IV VIS/SWIR broadband PDs and presents what we believe to be a novel approach to the design of low-cost broadband PDs.

Solid-State Lithium Batteries with Ultrastable Cyclability: An Internal-External Modification Strategy.

A commonly used strategy to tackle the unstable interfacial problem between Li1.3Al0.3Ti1.7(PO4)3 (LATP) and lithium (Li) is to introduce an interlayer. However, this strategy has a limited effect on stabilizing LATP during long-term cycling or under high current density, which is due in part to the negative impact of its internal defects (e.g., gaps between grains (GBs)) that are usually neglected. Here, control experiments and theoretical calculations show clearly that the GBs of LATP have higher electronic conductivity, which significantly accelerates its side reactions with Li. Thus, a simple LiCl solution immersion method is demonstrated to modify the GBs and their electronic states, thereby stabilizing LATP. In addition to LiCl filling, composite solid polymer electrolyte (CSPE) interlayering is concurrently introduced at the Li/LATP interface to realize the internal-external dual modifications for LATP. As a result, electron leakage in LATP can be strictly inhibited from its interior (by LiCl) and exterior (by CSPE), and such dual modifications can well protect the Li/LATP interface from side reactions and Li dendrite penetration. Notably, thus-modified Li symmetrical cells can achieve ultrastable cycling for more than 3500 h at 0.4 mA cm-2 and 1500 h at 0.6 mA cm-2, among the best cycling performance to date.

Silicon Nanowire Array Weaved by Carbon Chains for Stretchable Lithium-Ion Battery Anode.

To manufacture flexible batteries, it can be a challenge for silicon base anode materials to maintain structural integrity and electrical connectivity under bending and torsion conditions. In this work, 1D silicon nanowire array structures combined with flexible carbon chains consisting of short carbon nanofibers (CNFs) and long carbon nanotubes (CNTs) are proposed. The CNFs and CNTs serve as chain joints and separate chain units, respectively, weaving the well-ordered Si nanowire array into a robust and integrated configuration. The prepared flexible and stretchable silicon array anode exhibits excellent electrochemical performance during dynamic operation. A high initial specific capacity of 2856 mAh g-1 is achieved. After 1000 cycles, a capacity retention of 60% (1602 mAh g-1) is maintained. Additionally, the capacity attenuation is less than 1% after 100 bending cycles. This excellent cycling stability is obtained with a high Si loading of 6.92 mg cm-2. This novel approach offers great promise for the development of high-loading flexible energy-storage devices.

Effect of the bonding layer and multigrading layers on the performance of a wafer-bonded InGaAs/Si single-photon detector.

A wafer-bonded InGaAs/Si avalanche photodiode (APD) at a wavelength of 1550 nm was theoretically simulated. We focused on the effect of the I n 1-x G a x A s multigrading layers and bonding layers on the electric fields, electron and hole concentrations, recombination rates, and energy bands. In this work, I n 1-x G a x A s multigrading layers inserted between Si and InGaAs were adopted to reduce the discontinuity of the conduction band between Si and InGaAs. A bonding layer was introduced at the InGaAs/Si interface to isolate the mismatched lattices to achieve a high-quality InGaAs film. In addition, the bonding layer can further regulate the electric field distribution in the absorption and multiplication layers. The wafer-bonded InGaAs/Si APD, structured by a polycrystalline silicon (poly-Si) bonding layer and I n 1-x G a x A s multigrading layers (x changes from 0.5 to 0.85), displayed the highest gain-bandwidth product (GBP). When the APD operates in Geiger mode, the single-photon detection efficiency (SPDE) of the photodiode is 20%, and the dark count rate (DCR) is 1 MHz at 300 K. Moreover, one finds that the DCR is lower than 1 kHz at 200 K. These results indicate that high-performance InGaAs/Si SPAD can be achieved through a wafer-bonded platform.

Scalable fabrication of self-assembled GeSn vertical nanowires for nanophotonic applications.

In this work, scalable fabrication of self-assembled GeSn vertical nanowires (NWs) based on rapid thermal annealing (RTA) and inductively coupled-plasma (ICP) dry etching was proposed. After thermal treatment of molecular-beam-epitaxy-grown GeSn, self-assembled Sn nanodots (NDs) were formed on surface and the spontaneous emission from GeSn direct band was enhanced by ∼5-fold. Employing the self-assembled Sn NDs as template, vertical GeSn NWs with a diameter of 25 ± 6 nm and a density of 2.8 × 109 cm-2 were obtained by Cl-based ICP dry etching technique. A prototype GeSn NW photodetector (PD) with rapid switching ability was demonstrated and the optoelectronic performance of Ge NW PD was systematically studied. The GeSn NW PD exhibited an ultralow dark current density of ∼33 nA/cm2 with a responsivity of 0.245 A/W and a high specific detectivity of 2.40 × 1012 cm Hz1/2 W-1 at 1550 nm under -1 V at 77 K. The results prove that this method is prospective for low-cost and scalable fabrication of GeSn NWs, which are promising for near infrared or short wavelength infrared nanophotonic devices.

Broadband 400-2400†nm Ge heterostructure nanowire photodetector fabricated by three-dimensional Ge condensation technique.

A 2.7% tensile strained Ge/SiGe heterostructure nanowire (NW) is in-situ fabricated by a three-dimensional Ge condensation method. The NW metal-semiconductor-metal (MSM) photodetector demonstrates an ultra-broadband detection wavelength of 400-2400 nm, showing a high responsivity of >3.46×102 A/W with a photocurrent gain of >4.32×102 at 1550 nm under -2 V. A high normalized photocurrent to dark current ratio (NPDR) of 1.88×1011 W-1 at 1550 nm under -1 V is achieved. The fully complementary metal-oxide-semiconductor (CMOS) compatible, simple and scalable process suggest that the Ge heterostructure NW is promising for low cost, high performance near-infrared or short wavelength infrared focal plane array applications.

Low dark current broadband 360-1650 nm ITO/Ag/n-Si Schottky photodetectors.

This work designed an ITO/Ag/n-Si Schottky photodetector with broad wavelength detection and low dark current. The introduction of Ag interfacial layer and post rapid thermal annealing dramatically increase the barrier height of ITO/n-Si Schottky diode by 0.32 eV, leading to the 2300 × reduction of dark current. A well-behaved ITO/Ag (8 nm)/n-Si Schottky diode with a high rectification ratio ( ± 1 V) of 4 × 105 and low dark current (-1 V) of 9.2 nA was achieved. Such low dark current device spontaneously provides high sensitivity for visible/near infrared wavelength detection, in which substantial responsivity for wavelengths from 360 to 1650 nm was realized through both inter-band and internal photoemission. The design here provides an encouraging strategy for monolithically integrated pure Si photodetectors operating at long wavelength up to 1650 nm.

Room Temperature Electroluminescence from Tensile-Strained Si0.13Ge0.87/Ge Multiple Quantum Wells on a Ge Virtual Substrate.

Direct band electroluminescence (EL) from tensile-strained Si0.13Ge0.87/Ge multiple quantum wells (MQWs) on a Ge virtual substrate (VS) at room temperature is reported herein. Due to the competitive result of quantum confinement Stark effect and bandgap narrowing induced by tensile strain in Ge wells, electroluminescence from Γ1-HH1 transition in 12-nm Ge wells was observed at around 1550 nm. As injection current density increases, additional emission shoulders from Γ2-HH2 transition in Ge wells and Ge VS appeared at around 1300-1400 nm and 1600-1700 nm, respectively. The peak energy of EL shifted to the lower energy side superquadratically with an increase of injection current density as a result of the Joule heating effect. During the elevation of environmental temperature, EL intensity increased due to a reduction of energy between L and Γ valleys of Ge. Empirical fitting of the relationship between the integrated intensity of EL (L) and injection current density (J) with L~Jm shows that the m factor increased with injection current density, suggesting higher light emitting efficiency of the diode at larger injection current densities, which can be attributed to larger carrier occupations in the Γ valley and the heavy hole (HH) valance band at higher temperatures.