The structural and optical properties of nitrogenated amorphous carbon films, grown by rf-magnetron sputtering on silicon substrates, were studied by Raman and photoluminescence ͑PL͒ spectroscopy as a function of the nitrogen concentration and the substrate bias voltage V b . For films deposited with V b ϭ10 V, the photoluminescence emission was most intense at nitrogen concentrations in the carrier gas of 25% ͑75% Ar͒, while the intensity ratio I(D)/I(G) of the Raman bands of disordered graphite ͑D band͒ and graphite ͑G band͒ partially substituted by nitrogen exhibited a minimum simultaneously observed with a minimum of G-band frequency and a maximum of G-band width. Changes in spectral characteristics of Raman scattering at a concentration of 25% (Х30 at %) are indicative of an increase of sp 3 -bonded fraction and disorder. PL-enhancement coincides, in this case, with structural changes and is probably correlated to the substitution of nitrogen in the tetrahedraly bonded amorphous matrix. In the case of films deposited in a pure nitrogen atmosphere, N 2 ϭ100%, no significant PL-intensity changes appeared to exist between films deposited at low positive ͑10 V͒ and highly negative (Ϫ200 V) substrate bias. After several months of sample storage in air, samples grown at negative V b were found to preserve their structural and optical properties, while films grown at positive bias (V b ϭ10) and nitrogen concentrations in the carrier gas above 70% (Х40 at %) delaminated.

The electrical conductivity of heterojunctions of amorphous carbon (a-C) films (25 and 75 nm thick) grown on silicon by magnetron sputtering has been studied as a function of the applied electric field and temperature. At low electric fields and high temperatures, the conductivity exhibits thermally activated ohmic behaviour with activation energy 0.14 eV. At high electric fields, photoconductance measurements indicate that the conductivity is primarily due to a field-activated mobility with its activation energy decreasing as the electric field increases. At very high electric fields, band-to-band tunnelling is the dominant conduction mechanism. The mobility field-activated conduction model indicates an energy distribution of trapping states consisting of two exponential distributions. The exponential distributions correspond to tail states arising from clustering of sp 2 sites and to deep states caused by isolated sp 2 sites. Low-frequency noise measurements show that thicker a-C films contain a higher concentration of the trapping states. This result was explained by an increase of the sp 2 /sp 3 bonding ratio found from the analysis of Raman spectroscopic measurements.

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High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO) were successively electrodeposited in the form of columnar structures preferentially oriented along the 1011 crystallographic direction from aqueous solution of zinc nitrate (Zn(NO 3 ) 2 ) at negative electrochemical potential of E C = (−0.8)-(−1.2) V and moderate temperature of 80 • C on gallium rich (30% Ga) chalcopyrite selenide Cu(In,Ga)Se 2 (CIGS) with chemically deposited ZnSe buffer (ZnSe/Cu(In,Ga)Se 2 /Mo/glass). The aluminium doped ZnO layer properties have initially been probed by deposition of Al:ZnO/i-ZnO bilayers directly on Mo/glass substrates. The band-gap energy of the Al:ZnO/i-ZnO reference layers was found to vary from 3.2 to 3.7 eV by varying the AlCl 3 solute dopant concentration from 1 to 20 mM. The electrical resistivity of indium-pellet contacted highly doped Al:ZnO sheet of In/Al:ZnO/i-ZnO/Mo/glass reference samples was of the order ρ~10 −5 Ω·cm; the respective carrier concentration of the order 10 22 cm −3 is commensurate with that of sputtered Al:ZnO layers. For crystal quality optimization of the bilayers by maintenance of the volatile selenium content of the chalcopyrite, they were subjected to 2-step annealing under successive temperature raise and N 2 flux regulation. The hydrostatic compressive strain due to Al 3+ incorporation in the ZnO lattice of bilayers processed successively with 5 and 12 mM AlCl 3 dopant was ε h = −0.046 and the respective stress σ h = −20 GPa. The surface reflectivity of maximum 5% over the scanned region of 180-900 nm and the (optical) band gap of E g = 3.67 eV were indicative of the high optical quality of the electrochemically deposited (ECD) Al:ZnO bilayers.

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