In situ scanning tunneling microscopy study of C-induced Ge quantum dot formation on Si(100)

Abstract

Deposition of submonolayer coverages of C on Si͑100͒ prior to Ge growth leads to the formation of Ge quantum dots below the critical thickness for Ge islanding on bare Si͑100͒. In situ scanning tunneling microscopy reveals a high density of irregularly shaped islands for Ge coverages from 2.5 to 4 ML. Island sizes are broadly distributed between 10 and 25 nm. Keeping the C coverage constant and increasing the Ge coverage from 2.5 to 4 ML, the islands increase in height but their density remains constant (ϳ10 11 cm Ϫ2). At a Ge coverage of 5.8 ML, formation of larger ͑105͒-faceted islands is observed. Their density is reduced by a factor of 4 compared to smaller Ge coverages. Transmission electron microscopy shows that the nonfaceted islands are preserved after Si capping.

Phosphorus-mediated growth of Ge quantum dots on Si(001)

“…The Ge QDs of an areal density as high as 1.4 Â 10 11 cm À2 is reached. In contrast, dots with a similar areal density were also achieved by pre-depositing C for Ge coverages of 2.5-4 ML [8], but the size and shape of those Cinduced Ge dots are very different from ours. The C-induced Ge dots have a broad diameter distribution from 10 to 25 nm and a height of 1-2 nm.…”

“…The C-induced Ge dots have a broad diameter distribution from 10 to 25 nm and a height of 1-2 nm. The aspect ratio of these dots is about 1 10 ; significantly smaller than ours 1 6 : For a larger Ge coverage of 5.8 ML, the C-induced Ge dots show hutlike or pyramidal shape with an areal density of about 2.5 Â 10 10 cm À2 [8], much less than ours 1.4 Â 10 11 cm À2 .…”

“…Low temperature growth [2] can decrease dot diameter and enhance areal density, but may also degrade the crystallinity and luminescence properties. Mediated growth by surfactants and impurity atoms as well can change dot size and density [3][4][5][6][7][8][9]. Leifeld et al [8] attributed the extremely small dots induced by impurity C atoms to the compensation of the undulating surface strain field resulting from the submonolayer C coverage which is not uniformly distributed on the surface.…”

Quantitative investigation of the influence of carbon surfactant on Ge surface diffusion and island nucleation on Si(100)

“…17,18 A recent bottom-up strategy toward the engineering of the self-assembly process of Ge islands involves the use of carbon as a surfactant. The growth of C-induced SiGe islands has been extensively studied 3,[19][20][21][22][23] for the possibility to tailor their properties for potential application in nanoscale devices. 24 The growth mode of Ge on a Si͑100͒ surface precovered with a submonolayer amount of carbon, generating c͑4 ϫ 4͒ reconstructed domains, has been studied by Stoffel et al, 25 showing that the growth proceeds via a VolmerWeber ͑VW͒ mode.…”

Dosage dependence of Ge quantum dots grown on carbon-implanted Si substrates

“…However, this selfassembled method depends on lattice difference and varies in different material system, including III-V compounds. Recently, a new approach to scale down Ge dot sizes to less than 15 nm in diameter has been reported [1][2][3]. Predeposition of a submonolayer carbon atom on Si substrate results in significantly small and high density Ge dots because carbon atoms induce a strain field at the interface [1][2][3][4][5][6].…”