No abstract

By reactive magnetron sputtering from a ceramic SnO2:Ta target onto unheated substrates, X-ray amorphous SnO:Ta films were prepared in gas mixtures of Ar/O2(N2O, H2O). The process windows, where the films exhibit the lowest resistivity values, were investigated as a function of the partial pressure of the reactive gases O2, N2O and H2O. We found that all three gases lead to the same minimum resistivity, while the width of the process window is broadest for the reactive gas H2O. While the amorphous films were remarkably conductive (ρ ≈ 5 × 10−3 Ωcm), the films crystallized by annealing at 500 °C exhibit higher resistivities due to grain boundary limited conduction. For larger film thicknesses (d ≳ 150 nm), crystallization occurs already during the deposition, caused by the substrate temperature increase due to the energy influx from the condensing film species and from the plasma (ions, electrons), leading to higher resistivities of these films. The best amorphous SnO2:Ta films had a resistivity of lower than 4 × 10−3 Ωcm, with a carrier concentration of 1.1 × 1020 cm−3, and a Hall mobility of 16 cm2/Vs. The sheet resistance was about 400 Ω/□ for 100 nm films and 80 Ω/□ for 500 nm thick films. The average optical transmittance from 500 to 1000 nm is greater than 76% for 100 nm films, where the films, deposited with H2O as reactive gas, exhibit even a slightly higher transmittance of 80%. These X-ray amorpous SnO2:Ta films can be used as low-temperature prepared transparent and conductive protection layers, for instance, to protect semiconducting photoelectrodes for water splitting, and also, where appropriate, in combination with more conductive TCO films (ITO or ZnO).

Germanium nanocolumns grown by glancing angle deposition on Si(100) substrates and prepatterned substrates comprising of SiO2 nanospheres demonstrated an altered morphology that is greatly influenced by the substrate temperature (TS). Surface diffusion‐driven mass transport and increased adatom mobility at homologous temperatures TS/TM ≈ 0.34 and 0.39 (TM melting temperature of Ge) augmented fibrous‐columnar and intracolumnar growth, respectively. Further increment of the substrate temperature provoked column merging and column broadening. The degree of film crystallinity increased while TS increased from 200 to 340 °C, shifting the preferential crystallite orientation from (111) to (220).

A periodic arrangement of Ge nanorods on a Si(111) substrate was realized by glancing angle deposition (GLAD) onto honeycomb-like arranged Au hillocks formed using a self-assembled monolayer of polystyrene nanospheres as an evaporation mask. Additionally, a honeycomb-like arrangement of Au dots was used as an etch mask in a reactive ion beam etching process for pattern transfer procedure. Resulting honeycomb patterns consisting of Si hillocks within the Si(111) substrates were utilized to deposit Ge nanorods. Effective morphological variations in shape and dimension of GLAD-grown nanorods on honeycomb-like patterned substrates with both Au dot and Si dot arrays are strongly influenced by interseed distances, seed heights, and consequently shadowing lengths. For a large pattern period, it was observed that the usual triangular shape of the nanorod changed to a hexagonal shape as an effect of additional particle flux that reached the growing nanorod from the direction of second and third-nearest neighbors due to inadequate shadowing lengths and increased interseed condensation.

The nonlinear behavior of the current-voltage characteristics observed at low temperatures in p-Ge agrees well with the predictions of the Landau theory of critical and multicritical phase transitions.