Behavior of Sn atoms in GeSn thin films during thermal annealing: Ex-situ and in-situ observations

Thermally induced crystallization processes for amorphous GeSn thin films with Sn concentrations beyond the solubility limit of the bulk crystal Ge-Sn binary system have been examined by X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, and (scanning) transmission electron microscopy. We paid special attention to the behavior of Sn before and after recrystallization. In the as-deposited specimens, Sn atoms were homogeneously distributed in an amorphous matrix. Prior to crystallization, an amorphous-to-amorphous phase transformation associated with the rearrangement of Sn atoms was observed during heat treatment; this transformation is reversible with respect to temperature. Remarkable recrystallization occurred at temperatures above 400 degrees C, and Sn atoms were ejected from the crystallized GeSn matrix. The segregation of Sn became more pronounced with increasing annealing temperature, and the ejected Sn existed as a liquid phase. It was found that the molten Sn remains as a supercooled liquid below the eutectic temperature of the GeSn binary system during the cooling process, and finally, beta-Sn precipitates were formed at ambient temperature.status: publishe

Carrier and heat transport properties of polycrystalline GeSn films on SiO2

We evaluated the potential of polycrystalline (poly-) GeSn as channel material for the fabrication of thin film transistors (TFTs) at a low thermal budget (<600 C). Poly-GeSn films with a grain size of 50 nm showed a carrier mobility of 30 cm2 V -1 s -1 after low-temperature annealing at 475–500 C. Not only carrier mobility but also thermal conductivity of the films is important in assessing the self-heating effect of the poly-GeSn channel TFT. The thermal conductivity of the poly-GeSn films is 5–9 W m-1 K-1, which is significantly lower compared with 30–60 W m-1 K- 1 of bulk Ge; this difference results from phonon scattering at grain boundaries and Sn intersti- tials. The poly-GeSn films have higher carrier mobility and thermal conductivity than poly-Ge films annealed at 600C, because of the improved crystal quality and coarsened grain size resulting from Sn-induced crystallization. Therefore, the poly-GeSn film is well-suited as channel material for TFTs, fabricated with a low thermal budget.status: publishe

Carrier and heat transport properties of poly-crystalline GeSn films for thin-film transistor applications

status: publishe

Implantation and activation of phosphorus in amorphous and crystalline germanium layers

We have investigated phosphorus implantation and activation in amorphous and crystalline Ge layers, deposited on Si substrates. The structure of the Ge layer has only limited influence on the dopant profile and diffusion after annealing. Surprisingly, crystalline Ge layers show better electrical results after implantation and dopant activation. For the amorphous layer, the solid phase epitaxy process is influenced in the neighborhood of P, leading to point defects, which inhibit electrical activation. This result implies that when a crystalline Ge layer is amorphized during implantation of high doses, the dopant activation can be significantly reduced. Reduced temperature ramping improves activation of P in amorphous Ge layers.status: publishe