The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals. The relationships between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a catalyst or photocatalyst in aqueous redox reactions are reviewed. The compilation of band edge energies is based on experimental flatband potential data and complementary empirical calculations from electronegativities of constituent elements. Whereas most metal oxide semiconductors have valence band edges 1 to 3 eV below the H2O oxidation potential (relative to absolute vacuum scale), energies for conduction band edges are close to, or lower than, the H2O reduction potential. These oxide minerals are strong photo-oxidation catalysts in aqueous solutions, but are limited in their reducing power. Non-transition metal sulfides generally have higher conduction and valence band edge energies than metal oxides; therefore, valence band holes in non-transition metal sulfides are less oxidizing, but conduction band electrons are exceedingly reducing. Most transition-metal sulfides, however, are characterized by small band gaps (<1 eV) and band edges situated within or close to the H2O stability potentials. Hence, both the oxidizing power of the valence band holes and the reducing power of the conduction band electrons are lower than those of non-transition metal sulfides.

The absolute energy positions of conduction and valence bands of selected semiconducting minerals

Defect physics of the CuInSe2 chalcopyrite semiconductor

The defect structure of CuInS2. part I: Intrinsic defects

Tetragonal chalcopyrite CuIn-(S1−xSex)2 (0 ≤ x ≤ 1) nanocrystals were synthesized by reacting a mixture of CuCl, InCl3, S, and Se in the presence of oleylamine at 265 °C. The S/Se composition ratio in the CuIn(S1−xSex)2 could be tuned across the entire composition range of x from 0 to 1 by modulating the S/Se reactant mole ratio. The tetragonal lattice constants, that is, a and c, increase linearly with the increase of Se content, following Vegard’s law. The band gap energies of CuIn(S1−xSex)2 nanocrystals could be tuned in the range between 0.98 and 1.46 eV and change nonlinearly with respect to x, deriving a bowing parameter of 0.17 eV. In addition, the method developed in this study was scalable to achieve gram-scale production of stoichiometry-controlled CuIn(S1−xSex)2 and CuIn1−xGaxSe2 nanocrystals.

Quaternary CuIn(S1−xSex)2 Nanocrystals: Facile Heating-Up Synthesis, Band Gap Tuning, and Gram-Scale Production

The T(y) phase diagram of the alloys CuInyGa1−ySe2, prepared by the chemical vapor deposition method, is obtained from X-ray diffraction and differential thermal analyses. It is found that in addition to the chalcopyrite structure, a zincblende In2Se3-rich phase and a zincblende Ga2Se3-rich plus liquid two-phase field, are obtained. Also it is found that the variation of the lattice parameter ratio c/a is not linear with composition but varies from 1.96 to 2.00 as y is increased from 0.0 to 0.6 and c/a being equal to 2.00 in the composition range 0.6 ⪅ y ⪅ 1.0. The energy gap values, obtained from optical absorption measurements, follow a second-order equation in y giving a downward bowing parameter of about 0.15 eV.



Mittels Rontgenbeugung und differentieller Thermoanalyse wird das T(y)-Phasendiagramm von mit der CVD-Methode erhaltenen CuInyGa1−ySe2-Legierungen erhalten. Es wird zusatzlich zur Chalkopyritstruktur eine In2Se3-reiche Zinkblendephase und ein Zweiphasenfeld Ga2Se3-reiche Zinkblende plus Flussigkeit gefunden. Es wird ebenfalls gefunden, das die anderung des Gitterparameter-verhaltnisses c/a nicht linear in der Zusammensetzung ist, sondern von 1,96 bis 2,00 variiert, wenn y von 0,0 auf 0,6 ansteigt und c/a, gleich 2,00 im Zusammensetzungsbereich von 0,6 ⪅ y ⪅ 1,0 bleibt. Die Energieluckenwerte aus optischen Absorptionsmessungen folgen einer Gleichung zweiter Ordnung in y und ergeben einen nach unten gerichteten Bowingparameter von etwa 0,15 eV.

H. Neff

Papers

Sputter induced near surface electronic defects in group II–IV compound semiconductor alloys

II-VI and I-III-VI2 alloy crystals for photovoltaic applications