Semiconductor Nanowire Field-Effect Transistors as Sensitive Detectors in the Far-Infrared

Engineering detection dynamics in nanoscale receivers that operate in the far infrared (frequencies in the range 0.1–10 THz) is a challenging task that, however, can open intriguing perspectives for targeted applications in quantum science, biomedicine, space science, tomography, security, process and quality control. Here, we exploited InAs nanowires (NWs) to engineer antenna-coupled THz photodetectors that operated as efficient bolometers or photo thermoelectric receivers at room temperature. We controlled the core detection mechanism by design, through the different architectures of an on-chip resonant antenna, or dynamically, by varying the NW carrier density through electrostatic gating. Noise equivalent powers as low as 670 pWHz−1/2 with 1 µs response time at 2.8 THz were reached.

Design of Power Splitters Based on Hybrid Plasmonic Waveguides

Plasmonic power splitters based on hybrid plasmonic waveguides (HPWs) are proposed and investigated. The HPW consists of a high-permittivity semiconductor nanowire embedded in a SiO2 dielectric film near a metal surface. The propagation behaviors of Surface Plasmon Polaritons (SPPs) in HPWs are numerically simulated by the 3D finite-difference time-domain (FDTD) method. The incident field is transferred from the middle waveguide to the waveguides on both sides due to the coupling between adjacent waveguides. The intensity distributions can be explained by the multimode interference of SPPs supermodes. According to the field intensity distribution of five HPWs, we design a 1 × 3 power splitter and a 1 × 2 power splitter by reducing the length of some specific waveguides.

Absorption of Light in Finite Semiconductor Nanowire Arrays and the Effect of Missing Nanowires

When modelling the absorption in semiconductor nanowire (NW) arrays for solar cell and photodetector applications, the array is typically assumed to be infinitely periodic such that a single unit cell suffices for the simulations. However, any actual array is of a finite extent and might also show varying types of localized defects such as missing or electrically non-contacted individual NWs. Here, we study InP NWs of 2000 nm in length and 180 nm in diameter, placed in a square array of 400 nm in period, giving a rather optimized absorption of sunlight. We show that the absorption in the center NW of a finite N × N array converges already at N = 5 close to the value found for the corresponding infinite array. Furthermore, we show that a missing NW causes an enhanced absorption in neighboring nanowires, which compensates for 77% of the absorption loss due to the missing NW. In other words, an electrically non-contacted NW, which absorbs light but cannot contribute to the external short-circuit current, is a four times worse defect than a missing NW.