Tomas Kubart

A Detrimental Reaction at the Molybdenum Back Contact in Cu2ZnSn(S,Se)4 Thin-Film Solar Cells

Experimental proof is presented for a hitherto undetected solid-state reaction between the solar cell material Cu(2)ZnSn(S,Se)(4) (CZTS(e)) and the standard metallic back contact, molybdenum. Annealing experiments combined with Raman and transmission electron microscopy studies show that this aggressive reaction causes formation of MoS(2) and secondary phases at the CZTS|Mo interface during thermal processing. A reaction scheme is presented and discussed in the context of current state-of-the-art synthesis methods for CZTS(e). It is concluded that alternative back contacts will be important for future improvements in CZTS(e) quality.

Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides

Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides

Process stabilization and increase of the deposition rate in reactive sputtering of metal oxides and oxynitrides

Reactive sputtering processes normally exhibit undesirable hysteresis effects which are more pronounced for oxide than nitride deposition. We present a method to reduce and ultimately eliminate these effects for reactive sputtering of metal oxides and oxynitrides. This is achieved by the addition of nitrogen to the oxygen process, which in addition leads to a higher deposition rate. These observations can be qualitatively explained and theoretically predicted using an extension of the Bergs model to two different reactive gases. Although the nitrogen addition leads to pronounced changes of the processing characteristics, incorporation of nitrogen into the growing film is very small.

High rate reactive magnetron sputter deposition of titanium oxide

A systematic experimental study of reactive sputtering from substoichiometric targets of TiOx with x ranging from 0 to 1.75 is reported. Experimental results are compared with results from modeling. The developed model describes the observed behavior and explains the origins of the unexpectedly high deposition rate. The behavior is shown to originate from the presence of titanium suboxides at the target surface caused by preferential sputtering of the oxide. The model can be used for optimization of the target composition with respect to the deposition rate and film composition in a stable hysteresis-free reactive sputtering process.

Modelling of low energy ion sputtering from oxide surfaces

The main aim of this work is to present a way to estimate the values of surface binding energy for oxides. This is done by fitting results from the binary collisions approximation code Tridyn with data from the reactive sputtering processing curves, as well as the elemental composition obtained from x-ray photoelectron spectroscopy (XPS). Oxide targets of Al, Ti, V, Nb and Ta are studied. The obtained surface binding energies are then used to predict the partial sputtering yields. Anomalously high sputtering yield is observed for the TiO 2 target. This is attributed to the high sputtering yield of Ti lower oxides. Such an effect is not observed for the other studied metals. XPS measurement of the oxide targets confirms the formation of suboxides during ion bombardment as well as an oxygen deficient surface in the steady state. These effects are confirmed from the processing curves from the oxide targets showing an elevated sputtering rate in pure argon.

Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness

This letter presents a proof-of-concept process for tunable, self-limiting growth of ultrathin epitaxial NiSi2 films on Si (100). The process starts with metal sputter-deposition, followed by wet etching and then silicidation. By ionizing a fraction of the sputtered Ni atoms and biasing the Si substrate, the amount of Ni atoms incorporated in the substrate after wet etching can be controlled. As a result, the thickness of the NiSi2 films is increased from 4.7 to 7.2 nm by changing the nominal substrate bias from 0 to 600 V. The NiSi2 films are characterized by a specific resistivity around 50 mu Omega cm.

Optical properties and refractive index sensitivity of reactive sputtered oxide coatings with embedded Au clusters

In the present study, nanocomposite coatings of Au clusters embedded in two different oxides, TiO2 and Al2O3, were synthesized using pulsed DC magnetron sputtering. The depositions were carried out in three steps, by depositing the oxide, the Au clusters, and again the oxide. The deposition time of the Au clusters was varied in order to achieve different cluster sizes, morphologies, and nanocomposite topographies. The structure, microstructure, morphology, and the optical properties of the coatings were studied. With the increase in Au content, red-shifted surface plasmon resonance (SPR) peaks with higher intensity and increased widths were observed due to changes in the metal clusters sizes and morphology and due to interparticle effects. In order to relate the peculiar SPR extinction bands with the different clusters shapes and distributions, a simulation of the optical properties of the nanocomposites was performed making use of the Renormalized Maxwell-Garnett approach. A theoretical study concerning the refractive index sensitivity was made in order to predict the optimal coatings parameters for sensing experiments. The increased surface area and the strong SPR extinction bands make these coatings suitable for gas sensing and also catalysis, albeit many other application fields can be envisaged.

Experiments and modeling of dual reactive magnetron sputtering using two reactive gases

Reactive sputtering from two elemental targets, aluminum and zirconium, with the addition of two reactive gases, oxygen and nitrogen, is studied experimentally as well as theoretically. The complex ...

Deposition of highly textured AlN thin films by reactive high power impulse magnetron sputtering

Aluminum nitride thin films were deposited by reactive high power impulse magnetron sputtering (HiPIMS) and pulsed direct-current on Si (100) and textured Mo substrates, where the same deposition conditions were used for both techniques. The films were characterized by x-ray diffraction and atomic force microscopy. The results show a pronounced improvement in the AlN crystalline texture for all films deposited by HiPIMS on Si. Already at room temperature, the HiPIMS films exhibited a strong preferred (002) orientation and at 400 °C, no contributions from other orientations were detected. Despite the low film thickness of only 200 nm, an ω-scan full width at half maximum value of 5.1° was achieved on Si. The results are attributed to the high ionization of sputtered material achieved in HiPIMS. On textured Mo, there was no significant difference between the deposition techniques.

Synthesis of c-tilted AlN films with a good tilt and thickness uniformity

This communication describes a method for the deposition of thin piezoelectric AlN films with an inclined c-axis relative to the surface normal. Further, the tilt over the wafer is sufficiently uniform and exhibits a planar symmetry as well as good thickness uniformity. Careful control of both the nucleation and growth stages is needed to obtain tilted films with excellent quality. Thus in the nucleation state, it is argued that two independent mechanisms, namely seed layer texture and/or surface roughness, are mainly responsible for the subsequent titled growth. To achieve the latter, however, a certain directionality of the deposition flux is also necessary. The directionality of the deposition flux is achieved through the use of an array of linear magnetrons tilted under a certain angle with respect to the substrate normal.