Solution Processed Tellurium Single-Crystal Nanocubes and Polycrystalline Films for 2 µm Wavelength Infrared...

Tellurium (Te) is a p-type semiconductor with a narrow bandgap, promising for infrared optoelectronics. This work presents a solution-based synthesis of novel single-crystal Te nanocubes and polycrystalline films. Te is dissolved in ethylenediamine-ethanethiol, mixed with ethanolamine, and spin-coated to form nanocrystals and films. We achieved monodispersed single-crystal Te nanocubes ∼500-900 nm in size, confirmed by electron microscopy and diffraction. The crystal morphology can be tuned by the annealing temperature and air exposure time. We show patterning of Te nanocubes by exploiting the deposition dependence on the substrate's wetting properties. We also demonstrate ∼500 nm thick polycrystalline Te films processed in air at 150°C. The Te films exhibit p-type behavior, an electrical resistivity of 0.115 Ω·cm, and photoconductance at wavelengths up to 2100 nm without optical cavities or complex gain mechanisms. The films exhibit responsivities of 0.93 A W^{- 1} at 1720 nm and 137 mA W^{- 1} at 2100 nm under intensities of 0.98 and 6.4 mW/cm², respectively. The large dark current remains a limitation for the current photoconductor configuration, but device engineering can improve speed and ON/OFF ratio. Overall, this low-temperature method provides an alternative, cost-effective pathway for Te-based infrared optoelectronics beyond the operating ranges of Si, Ge, and conventional InGaAs.