Interband Photoconductivity of Metamorphic InAs/InGaAs Quantum Dots in the 1.3–1.55-μm Window

Abstract Photoelectric properties of the metamorphic InAs/In x Ga1 − x As quantum dot (QD) nanostructures were studied at room temperature, employing photoconductivity (PC) and photoluminescence spectroscopies, electrical measurements, and theoretical modeling. Four samples with different stoichiometry of In x Ga1 − x As cladding layer have been grown: indium content x was 0.15, 0.24, 0.28, and 0.31. InAs/In0.15Ga0.85As QD structure was found to be photosensitive in the telecom range at 1.3 μm. As x increases, a redshift was observed for all the samples, the structure with x = 0.31 was found to be sensitive near 1.55 μm, i.e., at the third telecommunication window. Simultaneously, only a slight decrease in the QD PC was recorded for increasing x, thus confirming a good photoresponse comparable with the one of In0.15Ga0.75As structures and of GaAs-based QD nanostructures. Also, the PC reduction correlate with the similar reduction of photoluminescence intensity. By simulating theoretically the quantum energy system and carrier localization in QDs, we gained insight into the PC mechanism and were able to suggest reasons for the photocurrent reduction, by associating them with peculiar behavior of defects in such a type of structures. All this implies that metamorphic QDs with a high x are valid structures for optoelectronic infrared light-sensitive devices

Thickness dependent structural parameters of kesterite Cu2ZnSnSe4 thin films for solar cell absorbers

The influence of thickness on the structural parameters, off stoichiometry and cation disorder in kesterite Cu2ZnSnSe4 films grown by flash deposition for solar cell absorbers is investigated employing X ray diffraction, energy dispersive X ray and Raman spectroscopies. It is shown that the lattice parameters of Cu2ZnSnSe4 changed depending on film thickness the 100 nm film turned out to be weakly stretched on the molybdenum coated glass substrates, while, in the thicker films, the compressive deformation is defined. The causes of the changes in film structure are outlined. Raman spectra revealed secondary phases like Cu2SnSe3 detecting reduction of its fraction with an increment in thickness; also, the SnZn antisite defect fraction decreases. Simultaneously, the share of disordered kesterite phase associated with CuZn antisite defects rises with thickness. The obtained results can be useful for optimization of technological growth proces