Quantum-confinement effect in individual Ge1−xSnx quantum dots on Si(111) substrates covered with ultrathin SiO2 films using scanning tunneling spectroscopy

Nakamura, Yoshiaki; Masada, Akiko; Ichikawa, Masakazu

doi:10.1063/1.2753737

Cited by 85 publications

(58 citation statements)

References 17 publications

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“…The direct energy band gap depends quadratically on the Sn composition (note the non-monotonic dependence of E g on x in Fig.3), because the bowing parameter in the direct band gap of the alloy has a strong influence. Experimentally, for dots of small diameters (<10 nm) absorption peaks between 1.5 eV and 2 eV were found [17], which agrees very well (perhaps surprisingly so, in view of the approximations involved) with the data for direct transitions given in Fig.3. Nevertheless, these dots are (predicted to be) an indirect band gap material.…”

Section: Resultssupporting

confidence: 77%

“…Clearly, such dots cannot be grown in Si in the same way as Sn dots are, because Ge is completely soluble in Si, in contrast to Sn. However, growth of Ge 1-x Sn x dots on [111] oriented Si substrate, rather than in a Si matrix, has been recently reported [17]. The dots are approximately hemispherical in shape, they are covered by SiO 2 , and are asserted to have a coherent interface with the underlying Si, and are therefore strained.…”

Section: Resultsmentioning

confidence: 99%

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Electronic structure and optical transitions in Sn and SnGe quantum dots in a Si matrix

Moontragoon

Vukmirović

Ikonić

et al. 2009

Microelectronics Journal

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Self-assembled quantum dots in the Si-Ge-Sn system have attracted research attention as possible direct band gap materials, compatible with Si-based technology, with potential applications in optoelectronics. In this work, the electronic structure near the Γ-point and the interband optical matrix elements of strained Sn and SnGe quantum dots in a Si matrix are calculated using the eight-band k.p method, and the competing L-valley conduction band states were found by the effective mass method. The strain distribution in the dots was found within the continuum mechanical model. The bulk band-structure parameters, required for the k.p or effective mass calculation for Sn were extracted by fitting to the energy band structure calculated by the non-local empirical pseudopotential method (EPM). The calculations show that the self-assembled Sn/Si dots, with sizes between 4 nm and 12 nm, have indirect interband transition energies (from the sizequantized valence band states at Γ to the conduction band states at L) between 0.8 to 0.4 eV, and direct interband transitions between 2.5 to 2.0 eV, which agrees very well with experimental results. Similar good agreement with experiment was also found for the recently grown SnGe dots on Si substrate, covered by SiO 2 . However, neither of these are predicted to be direct band gap materials, in contrast to some earlier expectations.

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Section: Resultssupporting

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Electronic structure and optical transitions in Sn and SnGe quantum dots in a Si matrix

Moontragoon

Vukmirović

Ikonić

et al. 2009

Microelectronics Journal

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“…It is interesting to note that, concerning the Ge nanodots on the Si x Ge 1−x O y layer, one can manipulate the individual nanodots as one likes by means of an STM tip [59]. On the other hand, nanodot arrays of direct-gap semiconductors (such as β-FeSi 2 and Ge 1−x Sn x ) have been successfully obtained on the SiO 2 monolayer in high densities [60,61], on which occurrence of the quantum size effect has been verified by means of STS and PES [62][63][64]. Close insight for the interface barriers and the transport mechanism which is available by the schemes described above is anticipated also for such new nanomaterials.…”

Section: Discussionmentioning

confidence: 99%

Growth, Quantum Confinement and Transport Mechanisms of Ge Nanodot Arrays Formed on a SiO2 Monolayer

Nakayama

Matsuda

Hasegawa

2008

e-J. Surf. Sci. Nanotechnol.

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In this review, recent findings on growth manners, quantum confinement phenomena, and carrier transport mechanisms of self-assembled Ge nanodots on an oxidized Si surface are summarized. A simple equation relating the dot size, which was estimated by STM images, with the Ge coverage was proposed. Quantum confinement was observed by photoemission spectroscopy (PES) and scanning tunneling spectroscopy (STS), and the actual height of the confining potential was determined from the dot-size vs. energy relationship through a three dimensional parabolic potential model. The transport mechanism of the nanodot arrays, which was estimated based on the measurements by a microscopic four-point-probe method, was distinct depending on the structure of the dot-substrate interface. All results suggest that the interface oxide layer and subnanometer-sized voids on it interconnecting the nanodots with the substrate not only regulate the quantized energy in the nanodots but also switch on/off carrier exchange between the nanodot and the substrate through variable interface potential barrier height.

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“…On the other hand, the STS measurements performed on Ge 1Àx Sn x nanodots (x ¼ 0:10 { 0:13), where the experimentally obtained values of E C corresponding to the range of nanodot sizes from 4 to 35 nm, 17) could also be used for a comparison with the value of ÁE s{s corresponding to the pyramidal Ge nanodot. As the gap width in the differential conductance, dI=dV curves of the STS measurements besides indicating the energy bandgap of the nanodot, also includes the value of E C .…”

Section: Analytical Expression For the Calculation Of The Energy Levementioning

confidence: 99%

“…While the quantum confinement effect in the Si, Ge and GeSn nanodots and their size-dependent electronic structure had been studied by various high spatial resolution spectroscopic techniques such as scanning tunneling spectroscopy (STS) at room temperature, 16,17) Fourier-transform photoabsorption spectroscopy, 18) photoemission spectroscopy, 19,20) X-ray absorption spectroscopy, 21) and the atomic force microscopy (AFM)/Kelvin probe technique. 22) However, to date no experimental investigations exist with which can identify the changes in the electronic structure of the Ge nanodot due to the shape of the nanodot.…”

Section: Introductionmentioning

confidence: 99%

Study of the Electronic Structure of Individual Free-Standing Germanium Nanodots Using Spectroscopic Scanning Capacitance Microscopy

Wong

2009

Jpn. J. Appl. Phys.

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High spatial resolution spectroscopic scanning capacitance microscopy (SCM) measurements at room temperature based on the differential capacitance (d C=d V ) versus probe tip-to-substrate bias characteristics, is directly used to characterize the electronic structure of a pyramidal and an ellipsoidal shaped germanium (Ge) nanodot (with physical sizes smaller than the Bohr exciton radius of Ge), among the arrays of Ge nanodots fabricated on a highly doped silicon substrate using an anodic alumina membrane as an evaporation mask. The ability to study the individual nanodots under the probe tip circumvents and isolates the statistical disorders encountered when studying large ensembles of size-dispersed nanodots. It is demonstrated that the spectra of the positive d C=dV peaks are reflective of the energetics of electron trapping in the quantized energy states inside the Ge nanodots. Furthermore, the spectroscopic SCM d C=dV profile is observed to be substantially influenced by the nanodot shape where the pyramidal Ge nanodot shows three distinct shells which are interpreted as the s-like ground state, the first excited p-like state and the second excited d-like state. On the other hand, the elliptical deformation of the ellipsoidal Ge nanodot breaks the shell structure which significantly affects its electronic structure. Using the spacing between the d C=d V peaks from the spectroscopic SCM measurements, an analytical expression is derived to calculate the energy separation between the different energy states in the Ge nanodots. #

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Quantum-confinement effect in individual Ge1−xSnx quantum dots on Si(111) substrates covered with ultrathin SiO2 films using scanning tunneling spectroscopy

Cited by 85 publications

References 17 publications

Electronic structure and optical transitions in Sn and SnGe quantum dots in a Si matrix

Electronic structure and optical transitions in Sn and SnGe quantum dots in a Si matrix

Growth, Quantum Confinement and Transport Mechanisms of Ge Nanodot Arrays Formed on a SiO2 Monolayer

Study of the Electronic Structure of Individual Free-Standing Germanium Nanodots Using Spectroscopic Scanning Capacitance Microscopy

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