The optical dielectric function of cerium oxide (CeO2) was characterized by the spectroscopic ellipsometry (SE) technique using the Kramers–Kronig relation and the Tauc–Lorentz (TL) dispersion model. Experimental results showed that the bandgap energy and refractive index at 632.8 nm of CeO2 are about 3.23 ± 0.05 eV and 2.33 ± 0.08, respectively. Based on the optical properties, the electrical conduction mechanisms in CeO2 thin films are determined to be Schottky emission in a medium electric field (0.5–1.6 MV cm−1) from 350 to 500 K and Poole–Frenkel emission in a high electric field (>2.36 MV cm−1) from 450 to 500 K. Accordingly, the conduction band offsets between Al and CeO2 and the trap energy level are about 0.62 ± 0.01 eV and 1.53 ± 0.01 eV, respectively.

A novel double-clad Cr4+:YAG crystal fiber is demonstrated by use of a codrawing laser-heated pedestal growth method. Up to 10 dB of gross gain at a wavelength of 1.52 microm is achieved at a pump power of 0.83 W, which, to our knowledge, is the first Cr4+-doped fiber amplifier in the optical fiber communication band.

InGaN p-n junction solar cells with various indium composition and thickness of upper p-InGaN and lower n-InGaN junctions are investigated theoretically. The physical properties of InGaN p-n junction solar cells, such as the short circuit current density (J SC), open circuit voltage (V oc), fill factor (FF), and conversion efficiency (η), are theoretically calculated and simulated by varying the device structures, position of the depletion region, indium content, and photon penetration depth. The results indicate that an In 0.6 Ga 0.4 N solar cell, with optimal device parameters, can have a J SC ~31.8 mA/cm 2 , V oc ~0.874 volt, FF ~0.775, and η ~21.5%. It clearly demonstrates that medium-indium-content InGaN materials have the potential to realize high efficiency solar cells. Furthermore, the simulation results, with various thicknesses of the p-InGaN junction but a fixed thickness of the n-InGaN junction, shows that the performance of InGaN solar cells is determined by the upper p-InGaN junction rather than the n-InGaN substrate. This is attributed to the different amount of light absorption in the depletion region and the variation of the collection efficiency of minority carriers.

In this study, we conducted numerical simulations with the consideration of microelectronic and photonic structures to determine the feasibility of and to design the device structure for the optimized performance of InGaN p-i-n single homojunction solar cells. Operation mechanisms of InGaN p-i-n single homojunction solar cells were explored through the calculation of the characteristic parameters such as the absorption, collection efficiency (χ), open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (FF). Simulation results show that the characteristic parameters of InGaN solar cells strongly depend on the indium content, thickness, and defect density of the i-layer. As the indium content in the cell increases, Jsc and absorption increase while χ, Voc, and FF decrease. The combined effects of the absorption, χ, Voc, Jsc, and FF lead to a higher conversion efficiency in the high-indium-content solar cell. A high-quality In0.75Ga0.25N solar cell with a 4 μm i-layer thickness can exhibit as high a conversion efficiency as ∼23%. In addition, the similar trend of conversion efficiency to that of Jsc shows that Jsc is a dominant factor to determine the performance of p-i-n InGaN solar cells. Furthermore, compared with the previous simulation results without the consideration of defect density, the lower calculated conversion efficiency verifies that the sample quality has a great effect on the performance of a solar cell and a high-quality InGaN alloy is necessary for the device fabrication. Simulation results help us to better understand the electro-optical characteristics of InGaN solar cells and can be utilized for efficiency enhancement through optimization of the device structure.

The air annealing induced grain growth from nano to microscale and a transformation sequence from Bi → β-Bi2O3 → γ-Bi2O3 → α-Bi2O3 was evident. All the annealed samples are oxygen-deficient, resulting in the appearance of a strong red emission band.