Enhanced Photothermal Conversion in Vertically Oriented Gallium Arsenide Nanowire Arrays

Abstract

The photothermal properties of vertically etched gallium arsenide nanowire arrays are examined using Raman spectroscopy. The nanowires are arranged in square lattices with a constant pitch of 400 nm and diameters ranging from 50 to 155 nm. The arrays were illuminated using a 532 nm laser with an incident energy density of 10 W/mm(2). Nanowire temperatures were highly dependent on the nanowire diameter and were determined by measuring the spectral red-shift for both TO and LO phonons. The highest temperatures were observed for 95 nm diameter nanowires, whose top facets and sidewalls heated up to 600 and 440 K, respectively, and decreased significantly for the smaller or larger diameters studied. The diameter-dependent heating is explained by resonant coupling of the incident laser light into optical modes of the nanowires, resulting in increased absorption. Photothermal activity in a given nanowire diameter can be optimized by proper wavelength selection, as confirmed using computer simulations. This demonstrates that the photothermal properties of GaAs nanowires can be enhanced and tuned by using a photonic lattice structure and that smaller nanowire diameters are not necessarily better to achieve efficient photothermal conversion. The diameter and wavelength dependence of the optical coupling could allow for localized temperature gradients by creating arrays which consist of different diameters.

Large-Area and Broadband Thermoelectric Infrared Detection in a Carbon Nanotube Black-Body Absorber

“…The high sensitivity at weak illumination power is considered to benefit from the extreme light absorption of CNTF and efficient thermoelectric conversion in the vertical metal/CNTF junction. 17 This feature could find practical significance in real-world photodetection since the infrared radiation to be detected/harvested is usually much weaker than the laser output. Moreover, this architecture might contribute to establishing mid-infrared single-photon detection, in analogy to a vertical indium phosphide nanowire array used for roomtemperature single-photon detection in the visible range.…”

“…Meanwhile, quantum-dot-based photodetectors also exhibit growing photosensitivity from visible to midinfrared range with a merit of low-cost solution processability, 12 but the limitations include high toxicity in heavyelement materials (i.e., mercury cadmium telluride, MCT) and narrow responsive spectra restricted by the finite bandgap and specific particle size. Synthesized by scalable methods (vapor− liquid−solid growth or wet-etching), vertically aligned nanowire arrays made of Si, 13 SiO 2 , 14 ZnO, 15 GaN, 16 GaAs, 17 and InAsSb 18 have been widely reported as anti-reflecting absorbers in the visible and infrared range. As a representative, carbon nanotube forest (CNTF), a self-aligned, densely packed three-dimensional (3D) architecture of carbon nanotubes (CNTs), is renowned for near unity absorption in an ultrabroad infrared range beyond far-infrared.…”

“…27 Walia et al discovered efficient photothermal conversion in vertical GaAs nanowires arrays under external light illumination and revealed a thermal gradient along the nanowires. 17 The demonstration of midinfrared and THz imaging with PTE photodetectors was achieved by Suzuki et al with a noise equivalent power <1 nW Hz −1/2 at the CNT/metal interface under ambient conditions. 24 To date, state-of-the-art mid-and far-infrared photodetectors are still hampered by several challenges: (1) High infrared reflection in low-dimensional materials due to high conductivities along zigzag directions of 2D sheets and along axis direction of one-dimensional (1D) nanowires; (2) Fieldeffect photodetectors have ∼μm scale channel length which requires highly focused laser beams as actuators and do not work well for weak infrared illumination; (3) Most current PTE photodetectors have a long lateral channel for effective heat dissipation and require localized illumination on p−n junctions or interfaces during photon detection.…”

“…Walia et al . discovered efficient photothermal conversion in vertical GaAs nanowires arrays under external light illumination and revealed a thermal gradient along the nanowires . The demonstration of mid-infrared and THz imaging with PTE photodetectors was achieved by Suzuki et al .…”

“…Light reflection is significantly suppressed in the self-assembled CNTF due to sparseness and vertical alignment of nanotubes . By employing this vertically aligned anti-reflecting nanowire array, , the macroscopic PTE photodetector has achieved high responsivity to an unfocused and broadband infrared light as low as 6.8 μW mm –2 , akin to many realistic scenarios. We find the optimized PTE performance yielded in a top conductive layer having the appropriate thickness and a low contact resistance.…”