Anomalous Urbach tail in GaAs.

Measurements of the electric field of zero-point optical phonons in GaAs quantum wells support the Urbach rule for zero-temperature lifetime broadening.

We study a specific type of lifetime broadening resulting in the well-known exponential "Urbach tail" density of states within the energy gap of an insulator. After establishing the frequency and temperature dependence of the Urbach edge in GaAs quantum wells, we show that the broadening due to the zero-point optical phonons is the fundamental limit to the Urbach slope in high-quality samples. ...

Effect of the Sulfur Concentration on the Optical Band Gap Energy and Urbach Tail of Spray-Deposited ZnS Films

Zinc sulfide (ZnS) films were deposited through a simple and low cost spray pyrolytic technique using mixed aqueous solutions of zinc nitrate and thiourea. The structural and optical properties of these films were investigated as a function of initial (Zn:S) molar ratio in the precursor solution, which varied between (1:1) and (1:3). X-ray diffraction (XRD) analysis revealed that wurtzite...

First-principles calculations of the Urbach tail in the optical absorption spectra of silica glass.

We present density-functional theory calculations of the optical absorption spectra of silica glass for temperatures up to 2400 K. The calculated spectra exhibit exponential tails near the fundamental absorption edge that follow the Urbach rule in good agreement with experiments. We discuss the accuracy of our results by comparing to hybrid exchange correlation functionals. We show that the Urb...

Anomalous di usion in quasi - geostrophic owJ

The Relationship between Structural and Optical Properties of GeO2-PbO Glasses

The structural and optical characterization of bulk GeO2-PbO glasses was the goal of this study. In this regard, six different (100-x)GeO2‌-xPbO (15<x<45) glasses were prepared by conventional melt quenching technique between two steel sheets. The produced samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and UV-Vis s...