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The study reports peculiar light absorption in LT-GaAs due to the prominence of arsenic vacancies (V As), interstitials (As i), and neutral arsenic anti-sites (As Ga 0) after UHV annealing under no Arsenic vapour pressure. We compared unannealed and annealed samples' transient absorption behaviour and vibrational modes through ultrafast transient absorption spectroscopy (UFTS) (over 2.75 eV–0.775 eV spectral range) and RAMAN spectroscopy, respectively. We found that the UHV heating of LT-GaAs has augmented the tensile strain in the film by incorporating split As i. However, there is overall defect mitigation, as evident from the reduced TO phonon peak (RAMAN) and ∼59 meV reduction in Fermi level (UFTS). Even with reduced defects, the UFTS data for the annealed sample shows a higher switching speed and responsivity (1.75 ps faster) in the NIR range and a higher photoconductive gain in the visible region. [ABSTRACT FROM AUTHOR]

The charge carrier and phonon dynamics are highly reliant on the material structural features, and understanding their dynamics help in interpreting the underlying phenomenological qualities of any material system. The phonon and carrier dynamics of Bi, Te, and BiTe 3 thin films formed on a Si (100) wafer through thermal evaporation are discussed in this article. The Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD) analysis are used to characterize the structural features of these films. The dynamics of charge carriers and phonons are further determined using femtosecond ultrafast transient absorption spectroscopy (UFTS). A comprehensive analysis of dynamics is carried out by performing multiple excitations probed in broad Near-Infrared (NIR) regimes. The current study would help collect the knowledge about the phonon and charge carrier dynamics of Bismuth, Tellurium, and Bismuth Telluride films for optical, spintronics, and terahertz applications. • Explored grain size and lattice strain-dependent phonon oscillations using ultrafast transient absorption spectroscopy. • As the grain size of thin films grows, so do the phonon oscillations. • The coherent optical phonons (COP) of Bismuth and Bismuth telluride oscillate at 2.31 THz and 1.1 THz, respectively. [ABSTRACT FROM AUTHOR]