Schottky barrier photodetector (PD) (tungsten/nickel/aluminum nitride) based on stacked tungsten gratings is reported in our work. The absorbance of the grating-based structure is obtained using rigorous coupled-wave analysis method. In addition, a responsivity value of 6.164 mA / W is calculated at λ = 559.38 nm based on Fowler’s model. More than three times enhancement in responsivity is achieved as compared with that of bulk structure (without grating) based Schottky barrier PD. In addition, a detectivity value of 33.11 × 1011 cm Hz1/2 / W is obtained. Furthermore, the effect of grating variables and incident angle on responsivity are also demonstrated. In future, the proposed structure can also be used as a plasmonic sensor, absorber, or spectral filter.
A multilayered fiber SPR sensor is studied with graphene multilayers for ethanol detection. The sensor design variants (graphene mono-, bi-, tri-, and quadra-layer) are simulated and analyzed at 1310 nm and 1550 nm wavelengths. The dynamic radiation damping in terms of variable temperature and Ag layer thickness is enforced on the sensor variants to lead to possible sensing performance enhancement. At an optimum radiation damping (ORD) condition (317.8 K temperature and 35.1 nm thick Ag layer at 1550 nm wavelength), the figure of merit (FOM) of the fiber (ZBLAN core and NaF clad) SPR sensor with graphene monolayer has the potential to reach to an ultrahigh magnitude of 27164.89 RIU-1 . The proposed sensor can be an important milestone in developing highly sensitive and accurate fiber optic chemical sensors.
A surface plasmon resonance (SPR) based fiber optic sensor is simulated and analyzed in near infrared (NIR) region for normal (N) and malignant human liver tissue (MET) detection. Proposed five layered sensor consists of samarium-doped chalcogenide core, silver layer (Ag) deposited on the polymer clad, followed by graphene monolayer and analyte layer. Transfer matrix method for N layer model has been used for normalized reflection coefficient (R) calculations for the proposed multilayer structure. Furthermore, sensor structure utilizes the selective ray launching where incident angle (α) is varied at fiber input end (angular interrogation) and power transmitted through sensing region of length ‘L’ is measured in dB. At resonance (i.e., α = αSPR), sharp power loss peak is obtained where, αSPR shifts to other angle (i.e. δαSPR) with a change in analyte refractive index (RI). The prime focus of the present study is to optimize the radiative damping (i.e., optimum radiative damping (ORD)) at Ag-graphene junction to bring significant enhancement in the sensor’s performance. At resonance condition, the interference between incident light and back-scattered light known as radiation damping is responsible for excessively large sensor’s figure of merit (FOM). Hence, the coupled role of metal layer thickness (dm) and wavelength (λ) with 2D material layer plays important role as extent of radiation damping changes significantly, which leads to massive increase in FOM. For the proposed sensor structure value of L/D is taken as 25 (D represents the fiber core diameter) achievable with various L and D combinations (e.g., L = 1 cm and D = 400 μm). The combination of dm = 35 nm and λ = 865 nm leads to a maximum FOM of 4910.32 RIU-1. The coupled effect of dm and λ leads to significantly higher value of FOM, enables the graphene-based fiber-optic sensor for biosensing and other applications.
Groups III-V compound semiconductors and their alloys are the main photodetecting elements for the entire fiber optic telecommunication band. However, the recent successful growth of Ge1-xSnx alloy on Ge virtual substrates on Si platform makes the group IV alloys a potential competitor. Ge1-xSnx alloy shows direct band gap and has an absorption coefficient almost 10 times higher than that of Ge. The photonic devices are complementary metal–oxide–semiconductor compatible. We have considered an n-Ge/p+-Ge1-xSnx/n-Ge1-xSnx heterojunction phototransistor (HPT) and studied the variations of terminal currents by considering the Gummel Poon model of HPT, and values of optical and current gains, photocurrent, and responsivity have been obtained. The performance of the device as a photodetector at fiber optic communication wavelengths seems quite encouraging to justify the use of GeSn-based HPTs as a replacement of III-IV semiconductor-based photodetectors.