A. B. Talochkin

Formation of nanocrystalline silicon films using high-dose H+ ion implantation into silicon-on-insulator layers with subsequent rapid thermal annealing

The formation of nanocrystalline Si films as a result of rapid thermal annealing of silicon-on-insulator structures implanted with high doses of H+ ions is studied. It is ascertained that the process of formation of Si nanocrystals is active even at temperatures of 300–400°C and is controlled by the hydrogen content in the silicon film and by the duration of annealing. It is concluded that the formation of nuclei of the crystalline phase occurs in silicon islands surrounded by microvoids and is caused by the ordering of Si-Si bonds in the course of release of hydrogen from the bound state. It is important that microvoids do not coalesce at temperatures up to ∼900°C in conditions of rapid thermal annealing. It is found that synthesized films exhibit luminescence in the green-orange region of the spectrum at room temperature.

Formation of a resonant microcavity in hydrogen ion-implanted silicon-on-insulator structures

Studies have been carried out on silicon-on-insulator (SOI) structures after the implantation of 24 keV, 3×1017u2002cm−2 hydrogen ions, and annealing at temperatures of 200−1000u2009°C in an argon ambient at either atmospheric pressure or under conditions of hydrostatic compression at 6 and 12 kbar. Photoluminescence (PL), Raman spectroscopy, secondary ion mass spectrometry, and high-resolution electron microscopy have been used to characterize the optical and structural properties of the resulting SOI structures. It has been found that annealing at a pressure above 6 kbar leads to a wavelength-selective increase (up to 37×) in the intensity of the PL from hydrogen implanted SOI samples. The appearance of fine structure in the PL spectrum correlates with the impeded outdiffusion of hydrogen from the implanted top Si layer as well as with the suppressed process of hydrogen microbubble formation in the near-surface region as a result of the annealing at a pressure P>6u2002kbar. These processes enable one to fabricate a...

Properties of Ge nanocrystals formed by implantation of Ge+ ions into SiO2 films with subsequent annealing under hydrostatic pressure

The influence of hydrostatic compression on the implantation-induced synthesis of Ge nanocrystals in SiO2 host was studied. It is found that high-temperature annealing under pressure leads to retardation of Ge diffusion in SiO2. It is shown that unstressed Ge nanocrystals are formed as a result of conventional annealing (under atmospheric pressure). Annealing under pressure is accompanied by formation of hydrostatically stressed Ge nanocrystals. The stress in Ge nanocrystals was determined from optical-phonon frequencies in the Raman spectra. The shift of Raman resonance energy (E1, E1 + Δ1) corresponds to the quantization of the ground-state energy for a two-dimensional exciton at the critical point M1 of germanium. It is ascertained that a photoluminescence band peaked at 520 nm is observed only in the spectra of the films which contain stressed Ge nanocrystals.

Lateral photoconductivity of multilayer Ge/Si structures with Ge quantum dots

Spectra of lateral photoconductivity of multilayer Ge/Si structures with Ge quantum dots, fabricated by molecular-beam epitaxy are studied. The photoresponse caused by optical transitions between hole levels of quantum dots and Si electronic states was observed in the energy range of 1.1–0.3 eV at T = 78 K. It was shown that the electronic states localized in the region of Si band bending near the Ge/Si interface mainly contribute to lateral photoconductivity. The use of the quantum box model for describing hole levels of quantum dots made it possible to understand the origin of peaks observed in the photoconductivity spectra. A detailed energy-level diagram of hole levels of quantum dots and optical transitions in Ge/Si structures with strained Ge quantum dots was constructed.

Photoconductivity of Si/Ge multilayer structures with Ge quantum dots pseudomorphic to the Si matrix

Longitudinal photoconductivity spectra of Si/Ge multilayer structures with Ge quantum dots grown pseudomorphically to the Si matrix are studied. Lines of optical transitions between hole levels of quantum dots and Si electronic states are observed. This allowed us to construct a detailed energy-level diagram of electron-hole levels of the structure. It is shown that hole levels of pseudomorphic Ge quantum dots are well described by the simplest “quantum box” model using actual sizes of Ge islands. The possibility of controlling the position of the long-wavelength photosensitivity edge by varying the growth parameters of Si/Ge structures with Ge quantum dots is determined.

Special features of photoluminescence in silicon-on-insulator structures implanted with hydrogen ions

The special features of photoluminescence spectra of silicon-on-insulator structures implanted with hydrogen ions are studied. An increase in the photoluminescence intensity with increasing hydrostatic pressure P during annealing and the formation of narrow periodic photoluminescence peaks in the spectral range from ∼500 to 700 nm are revealed for the structures annealed at P > 6 kbar. It is shown that the fine structure of the photoluminescence spectra correlates with the slowing-down of hydrogen effusion from the implanted samples and with the suppression of the formation of hydrogen microbubbles in the surface layer. These processes promote the formation of an optical resonator, with the mirrors formed by the “silicon-on-insulator-air” and “silicon-on-insulator-SiO2” interfaces and with the optically active layer formed by hydrogen ion implantation and subsequent annealing.

The Properties of Hydrostatically Strained Ge and Si Nanocrystals in Silicon Dioxide Matrix

The properties of Si and Ge nanocrystals with uniformly strained Si-Si and Ge-Ge bonds have been studied. The strained Si and Ge nanocrystals were produced by the implantation of Ge+ or Si+ ions in thermally grown SiO2 films subsequently annealed under hydrostatic pressure ranging from 1 bar to 12 kbar. Correlation between the formation of the hydrostatically strained nanocrystals and the features of the photoluminescence spectra has been observed. The obtained results are discussed in terms of broadening energy gap between the levels of electron states of the hydrostatically strained nanocrystals. This effect brings about direct radiative recombination.

Recrystallization of Silicon on Insulator Layers Implanted with High Doses of Hydrogen Ions

Recrystallization of the high-dose H + ion implanted silicon-on-insulator structures during rapid thermal annealing was studied. It was obtained, that recrysta llization process is strongly dependent on the hydrogen ion dose. Monocrystalline film, Si nanocrystals, and hydrogen bubble and void containing Si layer were produced after rapid thermal annealing of t he structures implanted to the doses of 1 × 10, 3 × 10, and 5 × 10 cm, respectively. It was concluded, that no coalescence of micropores took place during rapid thermal annealing at the temperatures up to ~900 C. Nucleation of crystalline phase occured inside the silicon isla d between micropores. That was originated from an ordering of Si-Si bonds as hydrogen atoms were leaving from bound state in the silicon network.

Raman and HRTEM investigations of Ge nanocrystals produced by Ge+-ion implantation of SiO2 films and subsequent high-pressure annealing

The properties of Ge nanocrystals formed in ion-implanted SiO2 films during annealing under elevated (12 kbar) hydrostatic pressure have been studied. It has been found that high-pressure heat treatment produces the nanocrystals with uniformly strained Ge-Ge bonds. Its average dimensions are larger than these obtained from unstrained nanocrystals produced during annealing at atmospheric pressure. The degree of deformation of the Ge nanocrystals has been determined using the Raman shift in the optical phonon frequency. The energy shift E1, E1 + Δ1 in the Raman resonance corresponds to quantization of the energy of the two-dimensional excitons M1 ground state of the Ge critical point. It has been established that the formation of strained nanocrystals correlates with the appearance of green PL band centered at 520 nm. Comparing the PL data with HRTEM results allows to suggest that green PL originates from stressed Ge nanocrystals of a radius of less than 6 nm.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.