Formation Mechanism of Self-Assembled Ge∕Si∕Ge Composite Islands

Abstract

This study investigated the formation mechanism of Ge/Si/Ge composite islands on Si(001) using a combination of selective wet chemical etching, atomic force microscopy and high-resolution transmission electron microscopy. After upper Ge-rich parts were removed by selective etching, the etched Ge/Si/Ge composite islands exhibited pyramid structures, which differed from the ring-like isocompositional profiles observed in conventional Ge islands. Experimental results demonstrated that the multilayered Ge/Si/Ge composite islands were almost defect-free and suffered from a serious SiGe intermixing during growth. The shape and size distribution of composite islands can be further controlled by tuning the island parameters. We elucidate these phenomena on the basis of low surface diffusivity and strain adjustment of the thin Si layer in composite islands. These composite islands were also found to exhibit an apparent enhancement and blueshift in photoluminescence emission. These results indicated that Ge/Si/Ge composite islands would be potentially useful as an optoelectronic material operating in the telecommunication range.

Composition and conductance distributions of single GeSi quantum rings studied by conductive atomic force microscopy combined with selective chemical etching

“…To realize these applications, it is essential to have good understanding of their composition distributions and electrical properties. Up to now, various methods have been employed to investigate the composition distributions of GeSi quantum structures [5][6][7][8][9][10][11][12][13][14][15][16], such as anomalous x-ray diffraction (XRD) [6,7], cross-sectional transmission electron microscopy (TEM) [8,9], tip-enhanced Raman spectroscopy [10], and atomic force microscopy (AFM) combined with selective chemical etching [11][12][13][14][15][16]. However, most of the research dealt with the composition distributions of GeSi QDs [6][7][8][9][10][11][12], and the results were usually obtained by averaging over an ensemble of QDs or limited to cross-sectional or surface profiles.…”

“…Up to now, various methods have been employed to investigate the composition distributions of GeSi quantum structures [5][6][7][8][9][10][11][12][13][14][15][16], such as anomalous x-ray diffraction (XRD) [6,7], cross-sectional transmission electron microscopy (TEM) [8,9], tip-enhanced Raman spectroscopy [10], and atomic force microscopy (AFM) combined with selective chemical etching [11][12][13][14][15][16]. However, most of the research dealt with the composition distributions of GeSi QDs [6][7][8][9][10][11][12], and the results were usually obtained by averaging over an ensemble of QDs or limited to cross-sectional or surface profiles. The quantitative threedimensional (3D) compositional profiles of GeSi QDs were recently reported by Rastelli et al by AFM imaging of the same QDs combined with selective chemical etching [13].…”

Interplay of Quantum Confinement and Strain Effects in Type I to Type II Transition in GeSi Core–Shell Nanocrystals

“…Si/Ge heterostructures have been fabricated using different techniques, such as molecular beam epitaxy, self-assembly, , ion beam and magnetic sputtering deposition, − chemical vapor deposition, , chemical synthesis, and gas-phase and nonthermal plasma synthesis. − They have been integrated into different technological devices, for instance, in high-speed and high-power field-effect transistors, − photodetectors, , linear and nonlinear optics devices, , solar cell systems, , nonvolatile memory, and thermoelectric devices.…”

Effect of strain on the electronic and optical properties of Ge–Si dome shaped nanocrystals

“…[6][7][8][9][10][11][12][13][14][15][16][17][18] Ge/Si based nanostructures are of interest due to their compatibility with the existing silicon-based technology. Furthermore, Ge/Si nanostructures with various shapes (domes, wire, lens, and pyramids) have been fabricated and integrated in optical and electrical devices using advanced fabrication techniques such as molecular beam epitaxy (MBE), 19 self-assembly, [20][21][22] and chemical vapor deposition (CVD). 8 These devices exhibit size dependent characteristics and show potential for future devices such as thin-film field effect transistors, 7 flash memory, 8,10 DotFETs, 23 photodetectors, 24 solar cells, 25,26 and quantum computers.…”