Boris Capon

Antimony sulfide as a light absorber in highly ordered, coaxial nanocylindrical arrays: preparation and integration into a photovoltaic device

We demonstrate the preparation of functional ‘extremely thin absorber’ solar cells consisting of massively parallel arrays of nanocylindrical, coaxial n-TiO2/i-Sb2S3/p-CuSCN junctions. Anodic alumina is used as an inert template that provides ordered pores of 80 nm diameter and 1–50 μm length. Atomic layer deposition (ALD) then coats pores of up to 20 μm with thin layers of the electron conductor and the intrinsic light absorber. The crystallization of the initially amorphous Sb2S3 upon annealing is strongly promoted by an underlying crystalline TiO2 layer. After the remaining pore volume is filled with the hole conductor by solution evaporation, the resulting coaxial p-i-n junctions display stable diode and photodiode electrical characteristics. A recombination timescale of 40 ms is extracted from impedance spectroscopy in open circuit conditions, whereas transient absorption spectroscopy indicates that holes are extracted from Sb2S3 with a lifetime of 1 ns.

Atomic layer deposition of ruthenium at 100 °C using the RuO4-precursor and H2

In this paper we report a low temperature (100 °C) ALD process for Ru using the RuO4-precursor (ToRuS™) and H2 as the reactant. The thermal decomposition behaviour of the precursor in the range of 50 °C–250 °C was investigated and it was found that thermal decomposition of RuO4 to RuO2 starts at a sample temperature of 125 °C. The RuO4/H2 process (0.0045 mbar/4 mbar) was attempted at temperatures below this decomposition limit and it was found that ALD growth of pure Ru is possible in a narrow temperature window near 100 °C. The growth rate during steady state growth was found to be 0.1 nm per cycle. The Ru film nucleated easily on a wide range of substrates (H-terminated Si, TiN, Pt and Al2O3). Although the films are grown at a low temperature, they are considerably pure and are of good quality as evidenced by a resistivity of 18 μΩ cm for an 18 nm film and a relative atomic concentration of impurities <5% as determined by XPS. It is hypothesized that the reaction of the RuO4 molecule with the Ru-surface leading to a monolayer of RuO2 is the mechanism that ensures a self-saturated behaviour of the first half reaction, which is a critical requirement to achieve a well-behaved ALD process.

Near room temperature plasma enhanced atomic layer deposition of ruthenium using the RuO4-precursor and H2-plasma

A plasma enhanced ALD process for Ru using RuO4 and H2-plasma is reported at sample temperatures ranging from 50 °C to 100 °C. At 50 °C, low impurity content Ru thin films were grown with a saturated growth rate of 0.11 nm per cycle. A study of the influence of various process parameters on the Ru film properties is given.

Annealing of sulfide stabilized colloidal semiconductor nanocrystals

The effect of thermal annealing on layers of CuInS2 nanocrystals (NCs) stabilized with (NH4)2S was investigated using in situ transmission electron microscopy (TEM), in situ X-ray diffraction (XRD), thermogravimetric analysis combined with mass spectrometry (TGA-MS) and X-ray photoelectron spectroscopy (XPS). It is shown that these inorganic, chalcogen containing ligands inhibit NC sintering up to 450 °C in an inert atmosphere. On the other hand, sintering can be promoted by annealing in hydrogen gas. A similar behavior is found with Cu2ZnSnSe4 and CdSe NCs. We attribute the inhibited sintering to the oxidation of the S2− originally stabilizing the NCs to sulfite or sulfate moieties, where oxidation is possible either by exposure of the films to air or by thermal decomposition of residual solvent molecules present in the film under inert conditions.

Low temperature thermal and plasma enhanced atomic layer deposition of ruthenium using RuO 4 and H 2 /H 2 -plasma

A thermal (RuO4/H2-gas) and a plasma enhanced (RuO4/H2-plasma) atomic layer deposition (ALD) process for deposition of Ru are reported. The ALD characteristics and film properties of both processes are presented. The thermal process is compared to the plasma process in terms of film properties as a function of sample temperature. Finally, a discussion about the probable ALD reaction mechanisms is given.