Performance Analysis of Different Slot Waveguide Structures for Evanescent Field Based Gas Sensor Applications

Slot waveguide has emerged as a potential candidate for the design of evanescent field absorption based photonic gas sensors, optical quantum information applications, etc. In this paper, three different slot waveguide structures, i.e., conventional slot, partial-strip-loaded slot, and full-strip-loaded­­­ slot waveguides have been explored to analyze their sensing performance for the methane gas. As the methane gas has the peak absorption at around 3.31 µm, therefore, this has been considered as the operating wavelength for the analysis. In anticipation of improvement in evanescent field ratio in slot region and hence, the sensing capabilities of the gas sensor, the slot waveguide structures have been designed by depositing the germanium layer over the calcium fluoride in different manners. To realize the significant evanescent field and sensitivity along with relatively low propagation loss, the suitable dimension of the slot waveguide structures has been chosen very judiciously. Several waveguide parameters, such as evanescent field ratio, propagation loss, and sensitivity have been chosen for the analysis and comparison of slot waveguide structures, by varying the arm-width and thickness of germanium layer. Simulation results have demonstrated that the full-strip-loaded slot waveguide has the superior performance in terms of higher evanescent field and higher sensitivity, which is followed by the partial-strip-loaded slot waveguide, even for the fixed target value of propagation loss. Moreover, the current analysis may be extended for the design of suitable photodetector that can further enhance the performance of the gas sensor.

Вертикальное упорядочение аморфных нанокластеров Ge в многослойных гетероструктурах a-Ge/a-Si:H

A multilayer heteronanostructure consisting of three pairs of amorphous silicon and amorphous germanium (a-Ge/a-Si:H) layers grown on a silicon substrate by low-frequency plasma-chemical deposition at temperature 225 oC was investigated. From the analysis of the Raman spectra, the phase composition of the silicon and germanium layers was determined, which showed that the layers are completely amorphous. The transmittance electron microscopy images show vertically ordered amorphous Ge nanoclusters initiated by local inhomogeneities in the first germanium layer, the lateral dimensions of which increase from the lower to the upper layer.

Резистивное переключение в мемристорах на основе гетероструктур Ag/Ge/Si

It is shown that two modes of resistive switching – bipolar and volatile unipolar – are peculiar for the Ag/Ge/Si structures with germinating dislocations in the germanium layer. In this modes the structures have stable states of electric current with ION/IOFF ~1.5–2.7. The volatile unipolar type of switching can be caused by the capture of charge carriers to deep levels associated with lattice defects in the Ge film of the memristor. At the same time, bipolar switching is associated with the drift of Ag+ ions along germinating dislocations.

Germanium/perovskite heterostructure for high-performance and broadband photodetector from visible to infrared telecommunication band

A high-performance and broadband heterojunction photodetector has been successfully fabricated. The heterostructure device is based on a uniform and pinhole-free perovskite film constructed on top of a single-crystal germanium layer. The perovskite/germanium photodetector shows enhanced performance and a broad spectrum compared with the single-material-based device. The photon response properties are characterized in detail from the visible to near-infrared spectrum. At an optical fibre communication wavelength of 1550 nm, the heterojunction device exhibits the highest responsivity of 1.4 A/W. The performance is promoted because of an antireflection perovskite coating, the thickness of which is optimized to 150 nm at the telecommunication band. At a visible light wavelength of 680 nm, the device shows outstanding responsivity and detectivity of 228 A/W and 1.6 × 1010 Jones, respectively. These excellent properties arise from the photoconductive gain boost in the heterostructure device. The presented heterojunction photodetector provides a competitive approach for wide-spectrum photodetection from visible to optical communication areas. Based on the distinguished capacity of light detection and harvesting from the visible to near-infrared spectrum, the designed germanium/perovskite heterostructure configuration is believed to provide new building blocks for novel optoelectronic devices.

Effect of strain in silicon nanotube FET devices for low power applications

In this paper, we have presented an analysis on the performance of a strained silicon channel in silicon nanotube FET (Si-NTFET) device. Si-NTFET devices have tube-shaped channel region and because of this conduction in the channel can be controlled in two ways from outside the tube and from inside (from hollow side) the tube which results in better control over the short channel effects (SCEs). Bi-axial strain induced into the device by the inclusion of silicon-–germanium layer in between the channel. Three-dimensional simulations of the structure are carried out using ATLAS TCAD simulator and the model is calibrated with respect to previously published experimental data. The transfer characteristics, drain induced barrier lowering (DIBL), threshold voltage, Ion and Ioff, subthreshold swing of the Si-NTFET and strained Si-NTFET devices are investigated. It is seen that in strained Si-NTFET, the drive capability and inversion charge density is much higher compared to that of Si-NTFET. Evaluation of electrical performances confirms that the DIBL and other SCEs are either reduced or remains the same. However, the use of strained Si-NTFET is more suited for high speed and low power applications.

Coexistence of strongly buckled germanene phases on Al(111)

We report a study of structural and electronic properties of a germanium layer on Al(111) using scanning tunneling microscopy (STM), low energy electron diffraction and core-level photoelectron spectroscopy. Experimental results show that a germanium layer can be formed at a relatively high substrate temperature showing either (3×3) or (√7×√7)R±19.1° reconstructions. First-principles calculations based on density functional theory suggest an atomic model consisting of a strongly buckled (2×2) germanene layer, which is stable in two different orientations on Al(111). Simulated STM of both orientations fit nicely with experimental STM images and the Ge 3d core-level data decomposed into four components is consistent with the suggested model.