Klaus J. Bachmann

Bio: Klaus J. Bachmann is an academic researcher from North Carolina State University. The author has contributed to research in topics: Chemical beam epitaxy & Epitaxy. The author has an hindex of 22, co-authored 105 publications receiving 1225 citations. Previous affiliations of Klaus J. Bachmann include Marshall Space Flight Center.

Efficient and stable solar cell by interfacial film formation

Abstract: The development of a new efficient and stable semiconductor-liquid junction solar cell is reported. The n-CuInSe2/I2-I−-Cu+-HI/C cell utilizes relatively inexpensive, non-toxic components and requires less stringent sealing which makes this cell a more feasible candidate for energy conversion device applications than its predecessors1–3. Initial output power measurements have already yielded a conversion efficiency of 9.5% under AM1 (Air Mass 1) conditions. After passage of 70,000 C cm−2 the cell continues to deliver virtually unchanged photocurrents at maximum power point. The performance is based on the in situ formation of an interfacial film that is stable in the operational range of the solar cell.

Sellmeier parameters for ZnGaP2 and GaP

Abstract: Sellmeier parameters are determined for the birefringent material ZnGaP2 and the singly refractive material GaP by the minimization of chi-square employing the Levenberg–Marquardt method. The distinguishing feature of the present work is that all five Sellmeier parameters are treated as adjustable. In previous work the Sellmeier parameter related to the restrahlen frequency was fixed and set equal for both ordinary and extraordinary waves in the birefringent material. The fitted results show there is approximately an 8% difference between the two. Taking this parameter as adjustable allows for a better fit on all other parameters.

Photoluminescence and photoconductivity of CuInSe2

Abstract: In this paper we report for the first time the results of photoluminescence (PL) and photoconductivity (PC) measurements on stoichiometric and well-defined off-stoichiometric copper indium diselenide. The energy gap at 10 K is 1.050\ifmmode\pm\else\textpm\fi{}0.005 eV and free-exciton emission at 1.030\ifmmode\pm\else\textpm\fi{}0.005 eV is the dominant feature in the PL spectra of stoichiometric nominally undoped ${\mathrm{CuInSe}}_{2}$. For Cu:In and metal:selenium ratios g1 recombination between Se-vacancy donors (-70 meV versus the conduction-band edge ${\mathrm{Cu}}_{\mathrm{In}}$ antisite acceptors [40 meV versus the valence-band edge (VBE)], and In-vacancy acceptors (80 meV versus the VBE), respectively, dominates the PL spectra. Excitation from the above two acceptor states contributes to the PC spectra with complimentary temperature dependence as compared to the deep emission.

Native defect related optical properties of ZnGeP2

Abstract: We present photoluminescence, photoconductivity, and optical absorption spectra for ZnGeP2 crystals grown from the melt by gradient freezing and from the vapor phase by high pressure physical vapor transport (HPVT). A model of donor and acceptor related subbands in the energy gap of ZnGeP2 is introduced that explains the experimental results. The emission with peak position at 1.2 eV is attributed to residual disorder on the cation sublattice. The lower absorption upon annealing is interpreted in terms of both the reduction of the disorder on the cation sublattice and changes in the Fermi level position. The n-type conductivity of ZnGeP2 Crystals grown under Ge-deficient conditions by the HPVT is related to the presence of additional donor states.

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

Abstract: 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.

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

Compound Copper Chalcogenide Nanocrystals

Abstract: This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...