[en] Solar cells based on polycrystalline thin-film Cu(In,Ga)Se₂ materials have recently achieved a new level of performance with a certified efficiency of 19.5%. In this contribution, some physical characteristics of the absorber materials (and devices) leading to such performance are presented. From the absorber composition and the device quantum efficiency data, we found that these materials have an atomic bulk composition of 0.88 < Cu / (In + Ga) < 0.95 and Ga / (In + Ga) ∼ 0.3 leading to an empirical effective band gap of 1.14 eV for which maximum performance is attained. These chalcopyrite absorber materials are also characterized by a strong <220/204> preferred orientation. Because of this key structural aspect found in our high-efficiency absorbers, we present a comparison for some physical characteristics of the absorber as related to typical preferred orientations observed in this material system, namely <112> and <220/204>. We find that <220/204>-oriented thin films are in general more homogeneous than <112>-oriented films in terms of their optoelectronic properties, and they lead to materials with a lower density of nonradiative recombination centers

[en] Defect characterization in molecular beam epitaxial (MBE) compositionally-graded In_xGa_1-xAs layers on GaAs substrates consisting different thickness of overshooting (OS) layers was carried out using cathodoluminescence (CL) and transmission electron microscopy (TEM). We found that the thickness of the OS layer influences not only stress but also lattice defects generated in a top InGaAs layer. While the top InGaAs layer with a thin OS layer is under compression and has mainly threading dislocations, the top layer with a thick OS layer is under tension and exhibits inhomogeneous strain associating with phase separation. We will discuss the mechanisms of defect generation and their in-plane distribution based on strain relaxation at the top and OS layers. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Cathodoluminescence (CL) spectrum imaging and grazing incidence X-ray diffraction (GIXRD) are employed to investigate nitride three-dimensional (3D) gallium structures. The metallic precursors are naturally obtained on a large variety of substrates by metal-organic chemical vapor deposition (CVD) with different shape/size controlled by the growth conditions, especially the temperature. These 3D metallic structures are subsequently exposed to a nitridation process in a conventional CVD reactor to form GaN nanocrystals, as confirmed by GIXRD measurements. CL spectroscopy shows visible light emission (2.5-2.8 eV) excited from the GaN in the 3D structures