Self-Assemble Formation of Ge Dots on Si(100) via C/Ge/C/Si Structure

Self-assemble formation of Ge quantum dots on Si is one of the promising candidates to implement optical devices, such as laser diodes [1], photo detectors [2] and solar cells [3], on a Si ULSI platform. It has been reported that the usage of sub-monolayer (ML) carbon (C) gave a beneficial way to form Ge dots as a result of c(4×4) reconstruction on Si(100) [4]. In our previous studies, self-assemble formations of Ge dots by C mediation were investigated as follow. In the case of sequential deposition of C and Ge on Si (Ge/C₁/Si structure) at low temperature and subsequent annealing, it was confirmed that Si-C bonds promoted to form Ge dots during solid phase epitaxy [5]. In the case of C₂/Ge/Si structure, an incorporation of C atoms into Ge layer during annealing induced to decrease the bulk free energy due to the formation of Ge-C bonds in the nucleation process, and led to scale down dot size and increase dot density [6]. On the basis of these backgrounds, by combining both structures, Ge dot formation via C₂/Ge/C₁/Si structure was investigated in this study. This is because the formation of Si-C bonds at the Ge/Si interface and Ge-C bonds in Ge dots is expected to help to obtain small and high-density Ge dots. The samples were prepared by solid-source molecular beam epitaxy system. C₂/Ge(7.5 ML)/C₁/Si(100) structures by changing C1 and C2 coverage were formed at substrate temperature of 200°C and were annealed at 650°C in the MBE chamber. As a result, small (20 nm) and dense (1.7 × 10¹⁰ cm^-2) Ge dots were obtained at C₁ = 0.25 ML and C₂ = 0.1 ML. This indicates that the C₂/Ge/C₁/Si structure, which enables to control the binding states of both Si-C and Ge-C bonds, is an effective way to form Ge quantum dots self-assembly. In the meeting, the influence of the relationship between C₁ and C₂, the dot formation mechanism related to C binding states, and the optimization of the C₂/Ge/C₁/Si structure will be presented in detail.

Acknowledgments

This study was partially supported by JSPS KAKENHI Grant Number 24246003 and 15H03554 and, JSPS Core-to-Core Program, A. Advanced Research Networks.

Reference

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