Tailoring bolometric properties of a TiOx/Ti/TiOx tri-layer film for integrated optical gas sensors.

In this paper, we systematically investigated tailoring bolometric properties of a proposed heat-sensitive TiOx/Ti/TiOx tri-layer film for a waveguide-based bolometer, which can play a significant role as an on-chip detector operating in the mid-infrared wavelength range for the integrated optical gas sensors on Ge-on-insulator (Ge-OI) platform. As a proof-of-concept, bolometric test devices with a TiOx single-layer and TiOx/Ti/TiOx tri-layer films were fabricated by varying the layer thickness and thermal treatment condition. Comprehensive characterization was examined by the scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses in the prepared films to fully understand the microstructure and interfacial properties and the effects of thermal treatment. Quantitative measurements of the temperature- and time-dependent resistance variations were conducted to deduce the minimum detectable change in temperature (ΔTmin) of the prepared films. Furthermore, based on these experimentally obtained results, limit-of-detection (LoD) for the carbon dioxide gas sensing was estimated to demonstrate the feasibility of the proposed waveguide-based bolometer with the TiOx/Ti/TiOx tri-layer film as an on-chip detector on the Ge-OI platform. It was found that the LoD can reach ∼3.25 ppm and/or even lower with the ΔTmin of 11.64 mK in the device with the TiOx/Ti/TiOx (47/6/47 nm) tri-layer film vacuum-annealed at 400 °C for 15 min, which shows great enhancement of ∼7.7 times lower value compared to the best case of TiOx single-layer films. Our theoretical and experimental demonstration for tailoring bolometric properties of a TiOx/Ti/TiOx tri-layer film provides fairly useful insight on how to improve LoD in the integrated optical gas sensor with the bolometer as an on-chip detector.

Arrayed MoS2 -In0.53 Ga0.47 As van der Waals Heterostructure for High-Speed and Broadband Detection from Visible to Shortwave-Infrared Light.

A high-speed and broadband 5 × 5 photodetector array based on MoS2 /In0.53 Ga0.47 As heterojunction is successfully demonstrated to take full advantage of the type-II band-aligned multilayer MoS2 /In0.53 Ga0.47 As. The fabricated devices exhibit good uniformity in the Raman spectrum and clear rectifying characteristics. The fabricated MoS2 /In0.53 Ga0.47 As photodetectors show good optical performances at a broad wavelength range showing high responsivities corresponding to the detectivity of ≈1010 Jones at -3 V for the incident broadband light from 400 to 1550 nm. A very fast photoresponse is also obtained with a small rise/fall time in the order of microseconds both for visible (638 nm) and shortwave infrared (1310 nm). Finally, the image scanning properties of MoS2 /In0.53 Ga0.47 As devices are demonstrated for visible and infrared light, indicating that the suggested device is one of the promising options for future broadband imager, which can be integrated on the focal plane arrays (FPAs).

Room temperature operation of mid-infrared InAs0.81Sb0.19 based photovoltaic detectors with an In0.2Al0.8Sb barrier layer grown on GaAs substrates.

In this paper, InAs0.81Sb0.19-based hetero-junction photovoltaic detector (HJPD) with an In0.2Al0.8Sb barrier layer was grown on GaAs substrates. By using technology computer aided design (TCAD), a design of a barrier layer that can achieve nearly zero valance band offsets was accomplished. A high quality InAs0.81Sb0.19 epitaxial layer was obtained with relatively low threading dislocation density (TDD), calculated from a high-resolution X-ray diffraction (XRD) measurement. This layer showed a Hall mobility of 15,000 cm2/V⋅s, which is the highest mobility among InAsSb layers with an Sb composition of around 20% grown on GaAs substrates. Temperature dependence of dark current, photocurrent response and responsivity were measured and analyzed for fabricated HJPD. HJPD showed the clear photocurrent response having a long cutoff wavelength of 5.35 µm at room temperature. It was observed that the dark current of HJPDs is dominated by the diffusion limited current at temperatures ranging from 200K to room temperature from the dark current analysis. Peak responsivity of HJPDs exhibited the 1.18 A/W and 15 mA/W for 83K and a room temperature under zero bias condition even without anti-reflection coating (ARC). From these results, we believe that HJPDs could be an appropriate PD device for future compact and low power dissipation mid-infrared on-chip sensors and imaging devices.

InAs/GaAs quantum dot infrared photodetector on a Si substrate by means of metal wafer bonding and epitaxial lift-off.

We report the fabrication of quantum dot infrared photodetectors (QDIPs) on silicon (Si) substrates by means of metal wafer bonding and an epitaxial lift-off process. According to the photoluminescence (PL) and x-ray diffraction measurements, the QDIP layer was transferred onto the Si substrate without degradation of the crystal quality or residual strain. In addition, from the PL results, we found that an optical cavity was formed because Pt/Au of the bonding material was served as the back mirror and the facet of the GaAs/air was served as the front mirror. The device performance capabilities were directly compared and peak responsivity was enhanced by nearly twofold from 0.038 A/W to 0.067 A/W.