In this work, we used the chemical vapor transport (CVT) method to grow PbI₂ crystals using iodine as a self-transporting agent. The crystals’ structure, composition, and uniformity were confirmed by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) measurements. We investigated the band gap energy using absorption spectroscopy measurements. Furthermore, we explored the temperature dependence of the band gap energy, which shifts from 2.346 eV at 300 K to 2.487 eV at 20 K, and extracted the temperature coefficients. A prototype photodetector with a lateral metal–semiconductor–metal (MSM) configuration was fabricated to evaluate its photoelectric properties using a photoconductivity spectrum (PC) and persistent photoconductivity (PPC) experiments. The resonance-like PC peak indicates the excitonic transition in absorption. The photoresponse I_Light/I_Dark-1 is up to 200%.

Photoconductivities of monocrystalline vanadium pentoxide (V2O5) nanowires (NWs) with layered orthorhombic structure grown by physical vapor deposition (PVD) have been investigated from the points of view of device and material. Optimal responsivity and gain for single-NW photodetector are at 7,900 A W-1 and 30,000, respectively. Intrinsic photoconduction (PC) efficiency (i.e., normalized gain) of the PVD-grown V2O5 NWs is two orders of magnitude higher than that of the V2O5 counterpart prepared by hydrothermal approach. In addition, bulk and surface-controlled PC mechanisms have been observed respectively by above- and below-bandgap excitations. The coexistence of hole trapping and oxygen sensitization effects in this layered V2O5 nanostructure is proposed, which is different from conventional metal oxide systems, such as ZnO, SnO2, TiO2, and WO3.

Raman scattering (RS) spectroscopy is a popular measurement technique that uses inelastic scattering of monochromatic light to study vibrational characteristics of a material system. A typical application of RS is for material structure determination. This paper describes the application of RS for the characterization of the preferable growth direction of well-aligned nanocrystals (NCs) deposited on sapphire substrates. The results indicate that RS could become a powerful technique for the quick determination of the NCs orientation. The redshifts and asymmetric linewidth broadening of the Raman features of RuO₂ NCs are analysed by a modified spatial correlation (MSC) model, which includes the factor of stress-induced shift. The usefulness of experimental RS together with the MSC model analysis as a nondestructive structural and residual stress characterization technique for NCs has been demonstrated.

Using room-temperature surface photovoltage spectroscopy, we have characterized several 30-layer stacked self-assembled $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot (QD) structures with different spacer layer (SL) thicknesses. Signals from every relevant portion of the samples, including QDs, wetting layer, and GaAs barrier have been observed. The strain-induced field for thinner SL is responsible for a significant modification of the band structure, possibly resulting in the appearance of an additional excited state lying higher than the second excited QD state. A peculiar feature below the fundamental transition is tentatively attributed to the optical absorption from uncoupled dots of which the density is significantly lower than that of vertically coupled ones. The spectra show blueshifted features with a decrease of the SL thickness, indicating that the materials intermixing between InAs QDs and GaAs SL are strongly driven by strain.

Photoluminescence (PL) of a strain-compensated Ge/Si_0.15Ge_0.85 multiple-quantum-well (MQW) structure was studied above room temperature, in the range of 300–440 K. Both direct and indirect radiative recombination PL features were observed. The relative intensity of direct to indirect recombination markedly increases with the increase of temperature. The enhancement of PL from direct recombination above RT has been attributed to the thermal excitation of carriers from L-type to Γ-type confined states. This extends the potential applicability of Ge/SiGe MQW as light emitters on a Si-based platform and is favorable for applications in metal-oxide-semiconductor integrated circuits which normally operate above RT.