NiMn2O4 (NMO) thin films with different thicknesses (0.47–1.90 μm) were grown on Yttria-stabilized zirconia (YSZ)(100) substrates by chemical solution deposition (CSD). The effects of different growth conditions on the structural and thermal properties of NMO films were investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements show that both the average grain size of the samples and the surface roughness become larger with an increase of thickness. Based on isothermal surface condition, the corresponding thermal conductivity of NMO films was extracted from the optothermal Raman measurement and the obtained thermal conductivity is ∼4.0 ± 0.8 W m−1 K−1 for micrometer-scale films, suggesting that the (grain) boundary phonon scattering plays a minor role to affect the thermal conductivity of thin NMO films.
High‐quality lattice‐matched and mismatched GaAs1–xSbx (0.37 < x < 0.57) epilayers are grown on InP by molecular beam epitaxy. The localized states are confirmed by the S‐shape behavior of the temperature‐dependent photoluminescence (PL). With the help of a model based on a redistribution process of localized excitons, the degree of carrier localization is estimated quantitatively. It is found that the degree of carrier localization reaches a maximum for the lattice‐matched sample with Sb = 47.7%, indicating that carrier localization effects are mainly due to compositional fluctuations. This result is corroborated by the power‐dependent PL. In addition, power‐dependent Raman measurements give a hint that the thermal conductivity of the lattice‐matched sample is ≈50% higher than that of lattice‐mismatched samples with Sb = 37.9% and 56.2%. Thus the abnormal S‐shape behavior (blue–redshift) that occurs in the power‐dependent PL from the lattice‐mismatched GaAsSb samples is attributed to both the lower degree of carrier localization and the enhanced laser heating effect caused by their smaller thermal conductivity.
High-quality lattice-matched and mismatched strained GaAs1−xSbx (0.37 < x < 0.57) sub-micrometer epilayers are grown on InP by molecular beam epitaxy. Based on a heat conduction model regarding the heat transfer process between the thin GaAsSb films and thick InP substrates, the corresponding thermal conductivity of GaAsSb epilayers was accurately extracted from the power and temperature micro-Raman measurement. Combined with time-domain thermoreflectance measurements, we found that in comparison to the lattice-matched sample with Sb = 47.7%, a significant reduction in thermal conductivity of the lattice-mismatched sample with Sb = 37.9% and Sb = 56.2% is observed. With the help of diffraction reciprocal space maps and temperature-dependent photoluminescence results, the reduction in thermal conductivity is attributed to lattice-mismatch-induced biaxial tensile and compressive strain that can cause the breakage of the cubic crystal symmetry and provoke more defects.
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