The optical response of 2D layered perovskites is composed of multiple equally-spaced spectral features, often interpreted as phonon replicas, separated by an energy Δ ≃ 15−40 meV, depending upon the compound. We show that the characteristic energy spacing, seen in both absorption and emission, is correlated with a substantial scattering response above ≃200 cm−1 (≃25 meV) observed in resonant Raman. This peculiar high-frequency signal, which dominates both Stokes and anti-Stokes regions of the scattering spectra, possess the characteristic spectral fingerprints of polarons. Notably, its spectral position is shifted away from the Rayleigh line, with a tail on the high energy side. The internal structure of the polaron consists of a series of equidistant signals separated by 25-32 cm−1 (3-4 meV), depending upon the compound, forming a polaron vibronic progression. The observed progression is characterized by a large Huang-Rhys factor (S >6) for all of the 2D layered perovskites investigated here, indicative of a strong charge carrier – lattice coupling.
We present result of optical studies on InAs/GaIn(As)Sb/InAs type II quantum wells predicted for the active region in interband cascade lasers, and further for laser-based gas sensors operating at room temperature in a broad wavelength range of mid infrared. Using photoreflectance spectroscopy supported by electronic structure calculations we determine the oscillator strength of the fundamental optical transition in structures with GaIn(As)Sb material of various compositions hole confinement layer. We show that incorporation of arsenic into this layer can affect several crucial properties significantly like transition wavelength and its probability, but also the structural material quality affecting the radiative efficiency. Also, by using photoluminescence we investigate one of the crucial parameters for the performance of interband cascade lasers, the spectral emission width of type II quantum wells constituting the laser active region.
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