Electrodeposited CuInSe2 Thin Film Junctions
We have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectroscopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction.
Schottky diode properties of CuInSe2 films prepared by a two-step growth technique
Abstract CuInSe 2 films were synthesized by a thermal evaporation method on both glass and Mo coated glass substrates. To obtain Al/CuInSe 2 /Mo Schottky diode, Al metal was evaporated on the upper surface of CuInSe 2 as a front contact and electrical properties of the structure were analyzed. The structural and optical behaviors of the CuInSe 2 thin films were also investigated. The X-ray diffraction studies showed that the chalcopyrite CuInSe 2 was obtained with a preferential orientation in the (1 1 2) plane with lattice parameters a and c as 0.577 and 1.161 nm, respectively. Mo back contact layer had a preferential orientation in the (1 1 0) plane. Scanning electron microscopy equipped with energy dispersive spectroscopy revealed an irregular and rough surface morphology with Cu-rich protruding regions. Optical studies showed the existence of three different band gaps, which were determined as 1.06, 1.17 and 1.39 eV, respectively. From the Hall Effect measurements, we determined the carrier concentration of CuInSe 2 films as 4.0 × 10 17  cm −3 . The electrical properties of the CuInSe 2 films were further studied by fabricating Al/p-CuInSe 2 /Mo structures and obtaining their forward and reverse bias current–voltage characteristics in a wide temperature range of 100–300 K, in steps of 25 K. A thorough analysis of the forward bias current–voltage characteristics based on thermionic emission theory showed that the zero bias barrier height increases while series resistance and ideality factor decreases with an increase in temperature. After a barrier height inhomogeneity correction, the Richardson constant and mean barrier height were found to be 34.71 A/cm 2  K 2 and 0.72 eV, respectively.
Optical properties and characterization of CuInSe2
Abstract CuInSe 2 single crystals grown from stoichiometric melts were studied by differential thermal analysis, X-ray diffraction, optical absorption and photoluminescence measurements. The resulting crystals were In-rich and exhibited n-type conductivity. From the optical measurements at low temperatures, a donor level around 12 meV and an acceptor level at about 40 meV, which have been attributed to indium atoms on copper sites and to copper vacancies respectively, appear as the predominant defect pair in our samples. Another defect level at about 70 meV, probably a donor level, has also been observed. Optical absorption measurements at room temperature show the presence of residual absorption, which has been attributed to direct-phononassisted transitions.