Germanium Self-Assembled Quantum Dots in Silicon for Nano- and Optoelectronics (original) (raw)
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Electroluminescence of Ge/Si self-assembled quantum dots grown by chemical vapor deposition
Applied Physics Letters, 2000
We have fabricated light-emitting diodes on Si operating in the near-infrared. The active region of the p -i -n diodes consists of Ge/Si self-assembled quantum dots. The Ge islands were grown in an industrial 200 mm single-wafer chemical vapor deposition reactor. The photoluminescence and the electroluminescence of the islands are resonant in the spectral range around 1.4-1.5 m wavelength. The electroluminescence is observed up to room temperature. © 2000 American Institute of Physics. ͓S0003-6951͑00͒00437-X͔
Formation and properties of selectively grown Ge/Si quantum dots
Superlattices and Microstructures, 2004
The selective epitaxial growth of Si layers and Ge quantum dots in windows patterned in oxidized Si(001) was investigated. The selectively deposited Si layers were found to develop towards truncated pyramids limited by {113} facets until the (001) top face disappears. By this way, the Ge dot formation on the (001) surface can then be controlled by adjusting the height of the truncated Si(001) pyramids grown prior to Ge deposition. By monitoring the facet formation during the growth of the Si layers, we showed that it is possible to form single or several Ge dots per window. We have then investigated the formation of Ge dots in stacked selectively grown layers. The Ge dots exhibit a vertical ordering along the growth direction. The optical and electrical properties of Ge dots grown both by selective growth and by self-assembly were investigated. The photoluminescence measurements showed a blue shift of the PL signal from selective Ge dots and the absence of PL from wetting layers as a result of dot size reduction and restricted surface. The forward current-voltage characteristics of Schottky contacts with Ge dots just below the interface exhibit some idealities which can be related to the presence of these dots and indicate that the inhomogeneities are stronger for samples with multilayers of Ge dots.
Structural and Optical Behavior of Germanium Quantum Dots
Chinese Physics Letters, 2012
Ge nanodots are grown on a Si(100) substrate by radio frequency magnetron sputtering deposition technique. The role of annealing temperature on structural and optical properties is studied. The formation of nanodots is confirmed by X-ray diffraction pattern and the particle size is estimated to be ~ 6.5 to 8.5 nm. The structure and optical characterizations are made using, Energy dispersive X-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, photoluminescence and Raman spectroscopy. The interface intermixing and the size of the nanodots are determined from Raman spectra and field emission scanning electron micrograph. Root mean square roughness and number density are found to be strongly influenced by annealing temperature. Photoluminescence spectra shows the strong emission peak at 3.21 eV accompanied by two weaker peaks at around 2.85 and 4.13 eV in the visible region. The red shift of the strong peak ~ 0.05 eV is attributed to the effect of quantum confinement.
Sb mediated formation of Ge/Si quantum dots: Growth and properties
Thin Solid Films, 2012
The phenomenon of surfactant (Sb) mediated formation of Ge/Si(100) islands (quantum dots) by means of molecular beam epitaxy is discussed. The limited diffusivity of Si and Ge adatoms caused by the Sb layer leads to a reduction of the size of Ge islands, the increase in the island density, and the sharpening of the interfaces of Ge islands. Thereby, a thin Sb layer is considered to be a powerful tool that provides more freedom in designing Ge quantum dot features. Ge quantum dots, grown via a thin Sb layer and embedded coherently in a Si p-n junction, are revealed to be the origin of the intense photo-and electroluminescence in the spectral range of about 1.5 μm at room temperature.
Ge quantum dots structural peculiarities depending on the preparation conditions
Journal of Synchrotron Radiation, 2003
Two-dimensional pseudomorphous Ge ®lms have been grown to a critical thickness of 4 monolayers (ML) on Si(001). As a result of continuing deposition, pyramid-like Ge islands were grown in Stranski±Krastanov mode. The pyramid-like Ge islands deposited on Si(001) substrate using molecular beam epitaxy at 573 K reveal quantum dots (QDs) properties. The local microstructure parameters determined by EXAFS spectroscopy are linked to nanostructure morphology and adequate models are suggested and discussed. The pure Ge nanoclusters are covered by a 1±2 ML ®lm with about 50% Si atom impurity caused by interface diffusion at 773 K. The in¯uence of the effective thickness of the Ge ®lm, Ge nanocluster sizes and Ge, Si deposition temperature on the QDs microstructure parameters is revealed. The ®rst attempt to extract information about the energy structure of the free states of the quantum dot from X-ray absorption spectra (XANES spectra) was made. It was established that the maximum in the XANES spectra of a sample doped with boron is due to the appearance of free levels in the quantum dots at a depth of the order of 1.1 eV from the bottom of the Ge conduction band.
Journal of Nanoscience and Nanotechnology, 2014
Controlled growth and characterization of germanium (Ge) and silicon (Si) nanostructure are the key issues for optoelectronic device fabrication. The role of post-annealing on the structural and optical properties of radio frequency (rf) magnetron sputtering grown of Ge and Si quantum dots (QDs) deposited on Si(100) substrate is studied. Atomic force microscopy confirmed the formation of Si and Ge QDs with estimated sizes lower than ∼ 17 nm and ∼ 14 nm respectively. The X-ray diffraction analysis revealed the formation of Si and Ge QDs accompanied by SiO 2 with estimated sizes of ∼ 5 and ∼ 7 nm for post-annealed Si and pre-annealed Ge QDs respectively. The room temperature photoluminescence spectra for Ge and Si demonstrated an emission peak at 3.20 and 2.72 eV respectively, which are attributed to the electron and hole recombination within QDs. A shift in the PL peak is observed through annealing which is ascribable to the changes in size of QDs and quantum confinement effect. The thermal annealing at 600 C is found to play an important role in controlling the shape, number density, root mean square (rms) roughness and the energy shift of the luminescence band for both Si and Ge QDs. The influence of annealing on growth morphology for Ge QDs is appeared to be stronger than Si.
Field and photo-field electron emission from self-assembled Ge–Si nanostructures with quantum dots
Progress in Surface Science, 2003
Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was 6 10 nm and cluster density was $10 10 cm À2. A stable field electron emission was obtained from these structures, showing current peaks in the current-voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current-voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 lm.
Local structure of self-organized uniform Ge quantum dots on Si(001)
Solid State Ionics, 2001
Pseudomorphous Ge films with pyramid-like Ge islands have been deposited on Si 001 substrate using molecular beam Ž . epitaxy at 3008C. The islands revealing quantum dots QD properties are self-organized during the growth in uniform Ge nanostructures with lateral sizes ; 15 nm and height ; 1.5 nm. Ge K XAFS measurements have been performed using total electron yield detection mode. It was established that the presence of an appreciable exchange of atoms between the Si and Ge phases decreases the elastic strains in the system during the deposition of the blocking Si Layer at 5008C. It has beenf ound that the Ge QD's are characterized by interatomic Ge-Ge distances of 2.41 A, which is 0.04 A less than that in bulk Ge. q
Ge–Si intermixing in Ge quantum dots on Si
2000
We have provided direct evidence for the presence of considerable Si–Ge intermixing in strained and unstrained Ge quantum dots deposited on Si (001) and Si (111). The local structure around Ge was probed by using Ge K-edge X-ray absorption spectroscopy; complementary evidence for intermixing was provided by AFM and STM studies. These results implied that the strain energy in the dots was reduced by Si atoms diffusing into the dots, resulting in a modified form of Stranski–Krastanov growth.
Self-Assembling Formation of Silicon Quantum Dot with Germanium Core by LPCVD
2002
The formation of nanometre-scale silicon dots with a germanium core on an ultrathin SiO 2 layer has been studied by controlling the early stages of low-pressure chemical vapour deposition (LPCVD) alternately using pure monosilane and 5% germane diluted with helium. From atomic force microscope observations and x-ray photoelectron spectroscopy measurements, the selective growth of Ge on pregrown Si dots and subsequent complete coverage with a Si cap have been confirmed. Cross-sectional transmission electron microscope images have shown the formation of isolated spherical nanocrystallites with Ge cores in contrast with hemispherical pregrown Si dots, implying a high structural strain at the interface between cladding Si and the Ge core. For multiply stacked structures of the dots with a Ge core, Raman-scattering spectra indicate that compositional mixing occurs partly at the Si/Ge-core interface during LPCVD.