Inelastic strain relaxation in the Ge quantum dot array

Abstract

Raman spectra of Si∕Ge∕Si (100) structures with Ge quantum dots (QDs) obtained by means of the low-temperature (200–300°C) molecular beam epitaxy are investigated. An extremely narrow Ge phonon line of the “anomalously” high intensity and a doublet structure of the Ge–Si mode are observed. These features are explained by the formation of a pure pseudomorphic state of a QD array to a Si substrate. Additional broad Ge phonon lines related to inelastic strain relaxation are found under the variation of growth conditions. The observed strain relaxation is strongly nonuniform for the two well known mechanisms of inelastic strain relaxation.

Formation of Ge nanoislands before the completion of a wetting layer in the Ge/Si(111) system

“…We consider intermixing of Ge and Si to be insignificant in our experiments because the Raman spectra do not contain phonon lines near 420 cm À1 , which are typical for the vibrations of Ge-Si bonds [13].…”

“…The electronic properties of strained pyramid-shaped Ge/Si (1 0 0) quantum dots were investigated [8][9][10][11]. Raman spectroscopy was successfully used to characterize the strain condition of Ge islands on Si(1 0 0) [12][13][14]. Ge nanoislands on Si(111) surface are less investigated.…”

70Ge nanocrystals in SiO2 films under neutron irradiation: A Raman and photoluminescence study

“…However, the discrepancy between calculation and experiment becomes larger with decreasing annealing temperature. It is understood that compressive stress can make the Raman peak blueshift [1,5]. We would get a higher wave number in stressed sample than that in stress-free sample.…”

“…Among them, ion-implantation is an effective method for its compatibility with Si technology and its implanting precision. A lot of work has been done to prepare natural Ge and 74 Ge nanocrystals by ion-implantation [5][6][7][8][9][10]. Since neutron irradiation has been widely used to improve properties of materials and the physical properties of isotopically enriched nanocrystals depend on their isotopic composition, the research on 70 Ge nanocrystals under neutron irradiation is important [11].…”

Temperature spectra of conductance of Ge/Si p-i-n structures with Ge quantum dots

“…The lack of size quantization effect in type 2 structure (absence of the second peak in the temperature dependence of conductivity) may be due to the accumulation of strains during the growth of successive Ge layers, which leads to an increase in the size of the quantum dots [11], and/or non-uniform strain relaxation, resulting in a large number of defects [12]. Introduction of thick Si spacer layers in type 3 structure should significantly reduce these factors, which leads to the appearance of the size quantization in Ge quantum dots and, thus, the appearance of the second peak in the temperature dependence of conductivity.…”