Study on the formation mechanism of bismuth-mediated Ge nanodots fabricated by vacuum evaporation

Abstract

Germanium (Ge) nanodots are expected for various applications. We have proposed a unique fabrication method for them with bismuth (Bi) mediation, and we have successfully formed high-density crystalline Ge nanodots by vacuum evaporation followed by low-temperature annealing. In this paper, we show the experimental results, such as dependence of the process condition on the nanodot structure and some results of the analyses of the nanodot samples. Then we discuss and propose a schematic formation mechanism for the nanodots as follows. First, during the deposition process, sequentially deposited Bi and Ge layers are mixed by solid phase diffusion and form an amorphous-alloy layer. Next, during the annealing process, crystallization of the Ge nanodots and desorption of the Bi proceeds; during this time, Bi and Ge exist as a solid-liquid coexistence phase in the alloy system, and this condition may enhance the phenomena.

Low-temperature formation of GeSn nanodots by Sn mediation

“…In contrast, we have reported that high-density Ge NDs are formed by Bi mediation with an annealing temperature of 400 °C. 28,30) Figure 9 shows a proposed schematic model of Bi-mediated Ge ND formation. 30) Bi is deposited before Ge deposition.…”

“…28,30) Figure 9 shows a proposed schematic model of Bi-mediated Ge ND formation. 30) Bi is deposited before Ge deposition. Because our vacuum evaporator was not equipped with an in situ observation system such as reflection high-energy electron diffraction (RHEED), we have not confirmed the surface structure just after the Bi deposition.…”

“…These results were confirmed by EDX analyses. 30) Since the deposition temperature of 130 °C is lower than the eutectic temperature of the Bi-Ge alloy system (271 °C), the formation of the alloy layer and the movement of the predeposited Bi are considered to have been caused by solidphase diffusion. In the annealing process at 400 °C, Bi existed as a liquid phase, and Ge existed as a solid phase.…”

“…Here, we note that we previously found large undulation with the amorphous BiGe layer in a study of Bi-mediated Ge ND formation, and pointed out this undulation (referred to as a dot-like structure) affected ND formation. 30) Because the undulation observed in the amorphous BiGe layer depends on the deposition temperature, 30) this effect may also take place for GeSn ND formation in conditions such as higher deposition temperatures.…”

Study on crystal growth of Ge/Si quantum dots at different Ge deposition by using magnetron sputtering technique

“…Over the past 30 years, Ge QDs have been grown mainly by materials equipment with low deposition rates (~ 0.01–0.04 Å/s), such as molecular beam epitaxy (MBE) 12 – 14 , chemical vapor deposition (CVD) 15 – 18 , and solid phase epitaxy (SPE) 19 , their corresponding complete technical system has been formed. In recent years, the idea of exploring the growth of Ge QDs has been further broadened, some work using typical physical vapor deposition (PVD) techniques such as ion beam sputtering 20 , high-vacuum evaporation 21 , e-gun deposition 22 , 23 to prepare Ge QDs has been reported.…”