Si Nanoislands Research Articles

Characterization of Structural Defects in Germanium Epitaxially Grown on Nano-Structured Silicon

Selective epitaxial growth of germanium (Ge) on nano-structured Si(001) wafers is studied to evaluate the applicability of the nano-heteroepitaxy (NHE) approach on Ge-Si system. Based on a gate spacer technology established in advanced silicon microelectronics periodic arrays of nano-scaled Si islands are prepared, where Ge is deposited on top by reduced pressure CVD. The spacing of these structures is 360 nm. The structural perfection of the deposited Ge is investigated by transmission electron microscopy and X-ray diffraction. It is found that SiO2used as masking material is responsible for the suppression of the desired strain partitioning effect according to NHE. Even for 10 nm oxide thickness, the lattice of Ge layers deposited on Si nano-islands relaxes completely by generation of misfit dislocations at the interface. The occurrence of additional structural defects like stacking faults and micro twins can be controlled by suited growth conditions.

Photoluminescence line width of self-assembled Ge(Si) islands arranged between strained Si layers

The effect of variations in the strained Si layer thicknesses, measurement temperature, and optical excitation power on the width of the photoluminescence line produced by self-assembled Ge(Si) nanoislands, which are grown on relaxed SiGe/Si(001) buffer layers and arranged between strained Si layers, is studied. It is shown that the width of the photoluminescence line related to the Ge(Si) islands can be decreased or increased by varying the thickness of strained Si layers lying above and under the islands. A decrease in the width of the photoluminescence line of the Ge(Si) islands to widths comparable with the width of the photoluminescence line of quantum dot (QD) structures based on direct-gap InAs/GaAs semiconductors is attained with consideration of diffusive smearing of the strained Si layer lying above the islands.

Comparative analysis of radiation effects on the electroluminescence of Si and SiGe/Si(001) heterostructures with self-assembled Islands

The effect of neutron radiation on the electroluminescence of the Si p-i-n diode containing a multilayered Ge/Si heterostructure with self-assembled nanoislands is studied. In comparison with bulk Si, the diodes containing Ge(Si) nanoislands exhibit a higher radiation hardness of the electroluminescence signal, which is attributed to spatial localization of charge carriers in the Ge/Si nanostructures. The spatial localization of charge carriers impedes their diffusion to radiation defects followed by nonradiative recombination at the defects. The results show the possibilities of using Ge/Si heterostructures with self-assembled nanoislands for the development of optoelectronic devices resistant to radiation.

Effect of irradiation on the luminescence properties of low-dimensional SiGe/Si(001) heterostructures

This study is concerned with the effect of irradiation on the luminescence properties of low-dimensional Si/Ge heterostructures with different degrees of spatial localization of charge carriers. It is shown that the radiation stability of Si/Ge heterostructures is improved with increasing efficiency of localization of charge carriers in the structures. The spatial localization of charge carriers in the SiGe nanostructures decreases the probability of nonradiative recombination of charge carriers at radiation defects produced in the Si matrix. It is demonstrated that, among the structures explored in the study, the highest radiation stability of luminescence properties is inherent in the multilayered structures containing self-assembled Ge(Si) nanoislands, in which the most efficient spatial localization of charge carriers is attained. In this case, the localization is three- and two-dimensional, correspondingly, for holes in the islands and for electrons in the Si layers that separate neighboring layers containing the islands.

THE DEPOSITION AND CONTROL OF SELF ASSEMBLED SILICON NANO ISLANDS ON CRYSTALLINE SILICON

The formation of nano sized Si structures during the annealing of silicon rich oxide (SRO) films was investigated. These films were synthesized by low pressure chemical vapor deposition (LPCVD) and used as precursors, a post-deposition thermal annealing leads to the formation of Si nano crystals in the SiO 2 matrix and Si nano islands ( Si nI ) at c-Si /SRO interface. The influences of the excess Si concentration, the incorporation of N in the SRO precursors, and the presence of a Si concentration gradient on the Si nI formation were studied. Additionally the influence of pre-deposition substrate surface treatments on the island formation was investigated. Therefore, the substrate surface was mechanical scratched, producing high density of net-like scratches on the surface. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) were used to characterize the synthesized nano islands. Results show that above mentioned parameters have significant influences on the Si nIs . High density nanosized Si islands can epitaxially grow from the c-Si substrate. The reported method is very simple and completely compatible with Si integrated circuit technology.

Controlling the Size and Density of Silicon Nanostructures by Incorporation of Nitrogen

AbstractSi nanostructures are prepared by thermal annealing of silicon rich oxide (SRO) which is deposited using low pressure (LP) CVD. X‐ray diffraction (XRD), Raman spectroscopy, infrared (IR) spectroscopy, and transmission electron microscopy (TEM) are used to characterize the structure of the Si nanocrystals and nanoislands. The density, crystallinity, and size of the Si nanoislands and Si nanocrystals can be controlled by the amount of nitrogen hosted in the SRO. The Si and SiO2 phase separation of the SRO during the annealing process is hindered by the incorporation of nitrogen.

Growth of metallic Au adsorbed islands on the Si(111)-(7 × 7) substrate

Au adsorbed(Au-Si) islands are formed by the deposition of Au atoms on the fabricated Si(111) surface, on which size selected Si nanoislands have been constructed. The growth of the Au-Si islands is subject to the substrate temperature, Ts. At Ts < 270 °C, the surface structure on Au-Si islands shows the Si(111) √3 × √3-Au structure, and some Au atoms form hole-island pairs on the flat surface because the diffusion length of the Au atoms is too short to reach to the Si nanoislands (about 10 nm). At Ts > 280 °C, The diffusion length of Au atoms becomes larger than a mean distance between the Si islands. At Ts > 300 °C, The surface structure on the Au-Si islands shows the Si(111) 5 × 2-Au structure, and some of the islands grow along one of the ⟨ 0 1̄ 1 ⟩ directions. The result means that the surface diffusion of Si atoms among the Au-Si islands is drastically enhanced, that hardly occurs at Ts < 270 °C.

Formation of silicon nanoislands on crystalline silicon substrates by thermal annealing ofsilicon rich oxide deposited by low pressure chemical vapour deposition

We report the preparation and characterization of Si nanoislands grown on a c-Sisubstrate by thermal annealing of silicon-rich oxide (SRO) films deposited using aconventional low pressure chemical vapour deposition (LPCVD) technique. Transmissionelectron microscopy revealed that a high density of Si nanoislands was formed onthe surface of the c-Si substrate during thermal annealing. The nanoislands arenanocrystallites with the same crystal orientation as the substrate. The strainat the c-Si/SRO interface is probably the main reason for the nucleation of theself-assembled Si nanoislands that epitaxially grow on the c-Si substrate. Theproposed method is very simple and compatible with Si integrated circuit technology.

Electronic structures of dangling-bond states on the Si nanoisland and the Si(111) 7×7 substrate

The electronic structure of the fabricated surface, on which uniform Si nanoislands are formed by a fine control of the growth conditions, has been studied in detail by using angle-resolved photoelectron spectroscopy. We found two surface components at ≈−0.57 and −0.35eV by decomposition of the photoelectron spectra in addition to three well-known dangling-bond states (center and corner adatoms and rest atom) in the 7×7 dimer-adatom stacking (DAS) fault unit cell. The energy of the additional surface components relative to wave number shows no dispersion, suggesting a localized surface state. By comparison with our scanning tunneling microscopy and scanning tunneling spectroscopy results, the additional two surface states are assigned to the dangling-bond states localized on the inner and outer adatoms of the rounded Si nanoislands.

Study of photoelectron spectroscopy from extremely uniform Si nanoislands on Si(111) 7×7 substrate

The electronic and structural properties of self-assembled Si nanoislands on a Si(111) 7×7 dimer-adatom-stacking fault substrate are investigated by photoelectron spectroscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy. Uniform Si nanoislands are formed on the Si(111) 7×7 substrate by control of the growth conditions. For the nanoislands fabricated on the substrate, the photoelectron spectrum shows a significant peak shift of ≈0.1eV, which is caused by a surface state related to a dangling bond at the nanoisland.

The electronic passivation properties of Si nanoislands on GaAs(110) step defects induced by cleaving

Scanning tunneling microscopy and spectroscopy (STS) have been used to investigate submonolayer Si depositions on clean cleaved GaAs(110). These studies focus on the effect of cleaving-induced step defects on GaAs(110), the resultant Si overlayer formation, and the electrical properties of the substrate/overlayer system formed at 280 °C. STS measurements at a clean step edge on GaAs(110) show that the Fermi level shifts towards midgap for both n and p type, while measurements performed on Si nanoislands at step edges show that the Fermi level reverts back towards its “ideal” position. Results indicate the passivation properties of Si on GaAs(110) when deposited under these conditions. Implications for use in laser facets are discussed.