Reactive dc magnetron sputtering of (GeOx–SiO2) superlattices for Ge nanocrystal formation

Abstract

The motivation of this work is the tailored growth of Ge nanocrystals for photovoltaic applications. The use of superlattices provides a reliable method to control the Ge nanocrystal size after phase separation. In this paper, we report on the deposition of (GeOx–SiO2) superlattices via reactive dc magnetron sputtering and the self-ordered Ge nanocrystal formation during subsequent annealing. Attention is directed mainly to define proper deposition conditions for tuning the GeOx composition between elemental Ge (x=0) and GeO2 (x=2) by the variation in the deposition temperature and the oxygen partial pressure. A convenient process window has been found which allows sequential GeOx–SiO2 deposition without changing the oxygen partial pressure during deposition. The phase separation and Ge nanocrystal formation after subsequent annealing were investigated with in situ x-ray scattering, Raman spectroscopy, and electron microscopy. By these methods the existence of 2–5 nm Ge nanocrystals at annealing temperatures of 600–750 °C has been confirmed which is within the superlattice stability range. The technique used allows the fabrication of superlattice stacks with very smooth interfaces (roughness<1 nm); thus the Ge nanocrystal layers could be separated by very thin SiO2 films (d<3 nm) which offers interesting possibilities for charge transport via direct tunneling.

p-Layer bandgap engineering for high efficiency thin film silicon solar cells

“…These two parameters characterize the amplitude ratio and the phase difference between the two polarizations. In any ellipsometry experiment, Fresnel reflection coefficient ratio ρ is defined as [32,33] …”

“…Careful line profiling study also reveals that these nanoparticles are conglomerates assembled by Sincs. The sample E also shows big conglomerated assembly of nanocrystallites in the amorphous Si matrix, revealing non-uniform nature of this sample [32]. It is believed that the surface morphology change is due to the increased boron-doping ratio for the sample E that suppresses uniform crystalline growth.…”

(Invited) Semiconductor Nanocrystals Embedded in High-k Materials

“…The inhibition of the crystallization of the Si containing nanoclusters cannot exclusively be explained by the increase of crystallization temperature for nano-objects, as shown by Zacharias et al (11), as Si clusters of similar size could be crystallized in SiO/SiO 2 superlattices at the same annealing temperatures (8). Hence, it can be argued, that the phase separation process of the ZrSiO layers was not completed during the high temperature anneal and therefore the remaining dopant concentration in the nanostructure inhibited the crystallization, as it was observed for high-k materials (3). To improve the understanding of this process, detailed work is ongoing.…”

“…However, the differentiation of the cubic and the tetragonal phase is difficult in the shown 2 θ range. Derived from earlier work (3,10), the presence of the tetragonal phase is more likely with regard to the thin layer thickness and the strong Si doping. No Si peak was found.…”

Germanium Quantum Dots Embedded in N‐Doping Graphene Matrix with Sponge‐Like Architecture for Enhanced Performance in Lithium‐Ion Batteries

“…Raman spectroscopy is employed to further confirm this composite, as shown in Figure 4. The sharp and weak peak observed at 288 cm −1 is attributed to Ge–Ge vibration;5, 15 this value is clearly smaller than that (≈300 cm −1 ) of bulk Ge, probably because of the ultra‐small size of the Ge quantum dots in the Ge/GN sponge 16. Two prominent peaks at 1328 and 1590 cm −1 correspond to the well‐documented D and G bands of GN, respectively.…”