An Ar‑H₂ plasma treatment was applied on an ultrathin RCA oxide to create well-passivated silicon wafers with symmetric c‑Si/SiO_x:H/a‑Si:H passivation layer stacks. The effective lifetime of these samples increased from 10 μs to 4 ms after annealing at 200 °C through Ar‑H₂ plasma treatment of the oxide. The results indicate that the plasma treatment can modify the RCA oxide and this enables atomic hydrogen diffusion at low annealing temperature, leading to a well passivated c‑Si/SiO_x:H interface. This might provide new possibilities to use wet chemical oxides in c-Si solar cells, for example as tunnel contacts.

We have critically evaluated the deposition parameter space of very high frequency plasma-enhanced chemical vapour deposition discharges near the amorphous to crystalline transition for intrinsic a-Si:H passivation layers on Si (1 1 1) wafers. Using a low silane concentration in the SiH₄-H₂ feedstock gas mixture that created amorphous material just before the transition, we have obtained samples with excellent surface passivation. Also, an a-Si:H matrix was grown with embedded local epitaxial growth of crystalline cones on a Si (1 1 1) substrate, as was revealed with a combined scanning electron and high-resolution transmission electron microscopy study. This local epitaxial growth was introduced by a decrease of the silane concentration in the feedstock gas or an increase in discharge power at low silane concentration. Together with the samples on Si (1 1 1) substrates, layers were co-deposited on Si (1 0 0) substrates. This resulted in void-rich, mono-crystalline epitaxial layers on Si (1 0 0). The epitaxial growth on Si (1 0 0) was compared to the local epitaxial growth on Si (1 1 1). The sparse surface coverage of cones seeded on the Si (1 1 1) substrate is most probably enabled by a combination of nucleation at steps and kinks in the (1 1 1) surface and intense ion bombardment at low silane concentration. The effective carrier lifetime of this sample is low and does not increase upon post-deposition annealing. Thus, sparse local epitaxial growth on Si (1 1 1) is enough to obstruct crystalline silicon surface passivation by amorphous silicon.

We report on the gas phase synthesis of highly crystalline and homogeneously alloyed Si_1−xGe_x nanocrystals in continuous and pulsed plasmas. Agglomerated nanocrystals have been produced with remarkable control over their composition by altering the precursor GeH₄ gas flow in a continuous plasma. We specially highlight that in the pulsed plasma mode, we obtain quantum-sized free standing alloy nanocrystals with a mean size of 7.3 nm. The presence of Si_1−xGe_x alloy particles is confirmed with multiple techniques, i.e. Raman spectroscopy, XRD (Xray diffraction) and HRTEM (high resolution transmission electron microscopy) studies, with each of these methods consistently yielding the same composition. The nanocrystals synthesized here have potential applications in band-gap engineering for multijunction solar cells.