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In this article we study the electroluminescence of p-i-n diode structures with Ge dots consisting of coherent three-dimensional small ͑pyramids͒ and larger ͑dome͒ islands. The Ge dots are formed through strain-induced islanding. The diode structures, including one layer with Ge dots, were deposited on Si mesas with variable areas in order to study the influence of limited area deposition on self-assembling. It was observed that the reduction of deposited area improves island uniformity. The combined analysis of island distribution and electroluminescence spectra has lead to the conclusion that domes in small diodes have a smaller Si content or are less relaxed than domes in larger diodes. The diodes are found to emit up to room temperature near the optical communication wavelength of 1.3 microns.

The influence of oxygen and nitrogen impurities on the performance of thin-film solar cells based on microcrystalline silicon (mu c-Si:H) has been systematically investigated. Single mu c-Si:H layers and complete mu c-Si:H solar cells have been prepared with intentional contamination by admitting oxygen and/or nitrogen during the deposition process. The conversion efficiency of similar to 1.2 mu m thick mu c-Si: H solar cells is deteriorated if the oxygen content in absorber layers exceeds the range from 1.2 x 10(19) to 2 x 10(19) cm(-3); in the case of nitrogen contamination the critical impurity level is lower ([N](critical)=6 x 10(18)-8 x 10(18) cm(-3)). It was revealed that both oxygen and nitrogen impurities thereby modify structural and electrical properties of mu c-Si:H films. It was observed that the both contaminant types act as donors. Efficiency losses due to oxygen or nitrogen impurities are attributed to fill factor decreases and to a reduced external quantum efficiency at wavelengths of >500 nm. In the case of an air leak during the mu c-Si:H deposition process, the cell performance drops at an air leak fraction from 140 to 200 ppm compared to the total gas flow during i-layer deposition. It is demonstrated that oxygen and nitrogen impurities close to the p/i-interface have a stronger effect on the cell performance compared to impurities close to the n/i-interface. Moreover, thick mu c-Si:H solar cells are found to be more impurity-sensitive than thinner cells

The electronic structure of the interface between the boron-doped oxygenated amorphous silicon “window layer” (a-SiOx:H(B)) and aluminum-doped zinc oxide (ZnO:Al) was investigated using hard x-ray photoelectron spectroscopy and compared to that of the boron-doped microcrystalline silicon (μc-Si:H(B))/ZnO:Al interface. The corresponding valence band offsets have been determined to be (−2.87 ± 0.27) eV and (−3.37 ± 0.27) eV, respectively. A lower tunnel junction barrier height at the μc-Si:H(B)/ZnO:Al interface compared to that at the a-SiOx:H(B)/ZnO:Al interface is found and linked to the higher device performances in cells where a μc-Si:H(B) buffer between the a-Si:H p-i-n absorber stack and the ZnO:Al contact is employed.

Articles you may be interested inHydrogenated amorphous silicon oxide containing a microcrystalline silicon phase and usage as an intermediate reflector in thin-film silicon solar cells Deposition of microcrystalline silicon prepared by hot-wire chemical-vapor deposition: The influence of the deposition parameters on the material properties and solar cell performance J. Appl. Phys. 98, 024905 (2005); 10.1063/1.1957128 Role of growth temperature and the presence of dopants in layer-by-layer plasma deposition of thin microcrystalline silicon (μc-Si:H) doped layersThe influence of atmospheric contaminants oxygen and nitrogen on the performance of thin-film hydrogenated amorphous silicon ͑a-Si: H͒ solar cells grown by plasma-enhanced chemical vapor deposition at 13.56 MHz was systematically investigated. The question is addressed as to what degree of high base pressures ͑up to 10 −4 Torr͒ are compatible with the preparation of good quality amorphous silicon based solar cells. The data show that for the intrinsic a-Si: H absorber layer exists critical oxygen and nitrogen contamination levels ͑about 2 ϫ 10 19 atoms/ cm 3 and 4 ϫ 10 18 atoms/ cm 3 , respectively͒. These levels define the minimum impurity concentration that causes a deterioration in solar cell performance. This critical concentration is found to depend little on the applied deposition regime. By enhancing, for example, the flow of process gases, a higher base pressure ͑and leak rate͒ can be tolerated before reaching the critical contamination level. The electrical properties of the corresponding films show that increasing oxygen and nitrogen contamination results in an increase in dark conductivity and photoconductivity, while activation energy and photosensitivity are decreased. These effects are attributed to nitrogen and oxygen induced donor states, which cause a shift of the Fermi level toward the conduction band and presumably deteriorate the built-in electric field in the solar cells. Higher doping efficiencies are observed for nitrogen compared to oxygen. Alloying effects ͑formation of SiO x ͒ are observed for oxygen contaminations above 10 20 atoms/ cm 3 , leading to an increase in the band gap.