Solution-Synthesized High-Mobility Tellurium Nanoflakes for Short-Wave Infrared Photodetectors

Abstract

Two-dimensional (2D) materials, particularly black phosphorus (bP), have demonstrated themselves to be excellent candidates for high-performance infrared photodetectors and transistors. However, high-quality bP can be obtained only via mechanical exfoliation from high-temperature- and high-pressure-grown bulk crystals and degrades rapidly when exposed to ambient conditions. Here, we report solution-synthesized and air-stable quasi-2D tellurium (Te) nanoflakes for short-wave infrared (SWIR) photodetectors. We perform comprehensive optical characterization via polarization-resolved transmission and reflection measurements and report the absorbance and complex refractive index of Te crystals. It is found that this material is an indirect semiconductor with a band gap of 0.31 eV. From temperature-dependent electrical measurements, we confirm this band-gap value and find that 12 nm thick Te nanoflakes show high hole mobilities of 450 and 1430 cm V s at 300 and 77 K, respectively. Finally, we demonstrate that despite its indirect band gap, Te can be utilized for high-performance SWIR photodetectors by employing optical cavity substrates consisting of Au/AlO to dramatically increase the absorption in the semiconductor. By changing the thickness of the AlO cavity, the peak responsivity of Te photoconductors can be tuned from 1.4 μm (13 A/W) to 2.4 μm (8 A/W) with a cutoff wavelength of 3.4 μm, fully capturing the SWIR band. An optimized room-temperature specific detectivity ( D*) of 2 × 10 cm Hz W is obtained at a wavelength of 1.7 μm.

Novel two-dimensional monoelemental and ternary materials: growth, physics and application

“…Interestingly, a 18.8-nm-thick 2D Te-based PD showed isotropic and anisotropic responsivity at wavelengths of 1.5 and 3 μm, respectively. It is indicated that the high anisotropy of the indirect bandgap was achieved for 2D Te nanosheet, while the direct bandgap was independent of the polarization of the infrared light [132]. Distinctly, Te also possesses an obvious photothermal effect in a wide broadband spectrum because of its narrow bandgap, which is already used in photothermal cancer therapy [159].…”

“…Therefore, Raman spectrum is a highly reliable technology to confirm the thickness range and chiralchain structure of Te. In view of the 1D helical chain along the c-axis and vdWs-like between chains in the triangular structure, 2D Te nanosheets exhibit unique anisotropy in bandgap, carrier mobility, phonon vibrations and optical absorption in the infrared region [132,147,154]. The angleresolved Raman peak intensities of different modes were observed in 13.5-nm Te nanosheets.…”

“…After that, Te nanostructures based on other substrate such as sapphire, graphene/4H-SiC and HOPG have also be studied in recent years [137][138][139][140][141][142][143]. In general, there are many kinds of synthetic methods, including physical vapor deposition (PVD) [135], MBE [138], LPE [144][145][146], hydrothermal reaction [131,132,147,148], CVD [130] and thermal evaporation deposition [149,150]. Without consideration of the crystal scale, both Lin et al and Wu et al demonstrated free-standing exfoliated Te nanosheets at the size of several hundred nanometers in polarized solvent by ultrasonic bath and centrifugation [144,146].…”

Emerging Applications of Elemental 2D Materials

“…Data from refs. . d) Plot of the specific detectivity D * of various photodetectors versus detected wavelength.…”

“…Data from refs. . e) Integration schemes for 2D‐material‐based saturable absorbers, showing: i) a schematic of black phosphorus coated fiber end and ii) its assembly into the photonic circuit through an adapter.…”