I. E. Tyschenko

Strong blue and violet photoluminescence and electroluminescence from germanium-implanted and silicon-implanted silicon-dioxide layers

The photoluminescence (PL) and electroluminescence (EL) properties of Ge-implanted SiO2 layers thermally grown on a Si substrate were investigated and compared to those of Si-implanted SiO2 films. The PL spectra from Ge-implanted SiO2 were recorded as a function of annealing temperature. It was found that the blue-violet PL from Ge-rich oxide layers reaches a maximum after annealing at 500 °C for 30 min, and is substantially more intense than the PL emission from Si-implanted oxides. The neutral oxygen vacancy is believed to be responsible for the observed luminescence. The EL spectrum from the Ge-implanted oxide after annealing at 1000 °C correlates very well with the PL one, and shows a linear dependence on the injected current. The EL emission was strong enough to be readily seen with the naked eye and the EL efficiency was assessed to be about 5×10−4.

Room‐temperature, short‐wavelength (400–500 nm) photoluminescence from silicon‐implanted silicon dioxide films

Experiments are reported which explore the possibility of using low‐temperature, multiple‐energy Si+ ion implantation into thin SiO2 films on Si and subsequent short‐time thermal processing to form silicon nanostructures capable of yielding a high‐intensity emission in the short‐wavelength part of the visible spectrum. A room‐temperature short‐wavelength PL band of high intensity was found after double implantation with energies of 200 and 100 keV at a temperature of −20 °C to a total dose of 4.8×10 16 cm−2 (atomic concentration about 2×1021 cm−3) and subsequent furnace annealing at 400 °C for 0.5 h in forming gas or by flash lamp annealing at 1050 °C for 20 ms.

Visible and near-infrared luminescence from silicon nanostructures formed by ion implantation and pulse annealing

Abstract Thermally-grown, 500 nm thick SiO2 films were implanted with 1.6 × 1016–1.6 × 1017 cm−2 Si+ ions at 100 and 200 keV. Then the samples were subjected to either rapid thermal annealing at 900–1200°C for 1s or flash-lamp annealing at 1050–1350°C for 20 ms. Photoluminescence (PL) measurements, Raman spectroscopy (RS) and high-resolution transmission electron microscopy (HREM) were employed for sample characterization. Weak room-temperature (RT) visible PL was observed before the transient anneals. RS revealed in these samples a broad band centered at 480 cm−1 indicating the presence of non-crystalline Si inclusions. The initial annealing steps decreased the PL intensity, but after 1200°C, 1 s or 1350°C, 20 ms the PL was found to increase considerably over the red and IR region with a maximum around 830 nm. Simultaneously, the Raman signal at 480 cm−1 diminished and additional scattering near 520 cm−1 arose pointing to the formation of Si nanocrystals. Formation of 2–6 nm Si nanocrystals was directly confirmed by HREM. It is difficult to explain their occurrence by diffusion-limited growth or solid-phase crystallization of α-Si phase inclusions, if any. A model is presented considering the Si nanocrystal formation via segregation of Si atoms from SiOx, rapid percolation-like formation of Si chains or fractals and finally their transformation to Si phase inclusions and nanocrystals. The dramatic increase in PL correlated with the Si nanocrystals formation is considered to support the idea of quantum-confined origin of PL.

Annealing effects in light-emitting Si nanostructures formed in SiO2 by ion implantation and transient preheating

A dose of 1.6 × 1017 cm−2 Si+ ions was implanted in 500-nm-thick SiO2 layers with subsequent transient annealing at different temperatures. After the highest temperatures light-emitting Si nanoclusters were found that were formed in SiO2. Then all the layers were subjected to isochronal (30 min) furnace anneals and their properties were controlled by room temperature photoluminescence (PL) and Raman spectroscopy. The PL intensity from Si nanocrystal-containing layers progressively decreased with an increase in the anneal temperature (Ta) up to 800–900°C, but rapidly arose again in the Ta range of 1000–1150°C. Raman scattering has shown that Si nanocrystals vanish at Ta ∼ 800°C and that the amorphous silicon signal reappears. When the initial transient annealing failed to form Si nanocrystals, the furnace heat treatment at Ta < 700°C gave rise in PL intensity followed by its drop at Ta ∼ 800–900°C and a strong increase at Ta ∼ 1000–1150°C. The disappearance of Si nanocrystals and PL is considered to result from low stability of the smallest crystallites quenched in SiO2 by transient processing. When Si nanocrystals were not induced by transient preheating, the increase in Ta supposedly led to percolation-like formation of Si inclusions, their transformation to amorphous Si phase nanoprecipitates and, finally, to Si nanocrystals. For all the samples the formation of nanocrystals at Ta = 1000–1150°C was provided by the increase in their stability due to diffusion-limited grain growth. The results obtained are considered to support the idea of quantum-confined origin of PL.

Enhancement of the intensity of the short-wavelength visible photoluminescence from silicon-implanted silicon-dioxide films caused by hydrostatic pressure during annealing

We have studied the influence of the hydrostatic pressure during annealing on the intensity of the visible photoluminescence (PL) from thermally grown SiO2 films irradiated with Si+ ions using double-energy implants at 100 and 200 keV and ion doses ranging from 1.2×1016 to 6.3×1016 cm−2. Postimplantation anneals have been carried out in an Ar ambient at temperatures Ta of 400 and 450 °C for 10 h at both atmospheric pressure and hydrostatic pressures of 0.1, 10, 12, and 15 kbar. It has been found that the intensity of the ultraviolet (∼360 nm), blue (∼460 nm), and red (∼600 nm) PL emission bands increases with raising hydrostatic pressure whereby the PL peaks retain their wavelength positions. The results obtained have been interpreted in terms of enhanced, pressure-mediated formation of ≡Si–Si≡ centers and small Si clusters within metastable regions of the ion-implanted SiO2.

Photoluminescence and electroluminescence investigations at Ge-rich SiO2 layers

Strong blue and violet photo (PL) and electroluminescence (EL) at room temperature was obtained from SiO 2 -films grown on crystalline Si, which were either single (SI) or double implanted (DI) with Ge ions and annealed at different temperatures. The PL spectra of Ge-rich layers reach a maximum after annealing at 500-700 C for DI layers or 900-1000°C for SI layers, respectively. Both, PL and EL of 500 nm thick Ge-rich layers are easily visible by the naked eye at ambient light due to their high intensity. Based on excitation spectra we tentatively interpret the blue PL as due to the oxygen vacancy in silicon dioxide. The EL spectrum of the Ge-implanted oxide correlates very well with the PL one and shows a linear dependence on the injected current over three orders of magnitude. For DI layer much higher injection currents than for SI layers can be achieved. An EL efficiency in the order of 10 -4 for Ge - -implanted silicon dioxide was determined.

A study of the blue photoluminescence emission from thermally-grown, Si+-implanted SiO2 films after short-time annealing

Abstract Thermal SiO 2 films have been implanted with Si + ions using double-energy implants (200 + 100 keV) at a substrate temperature of about −20°C to total doses in the range 1.6 × 10 16 −1.6 × 10 17 cm −2 followed by short-time thermal processing, in order to form a Si nanostructure capable of yielding blue photoluminescence (PL). The intensity and the peak position of the PL band have been investigated as a function of ion dose, manner of heat treatment, anneal time and anneal temperature. For the formation of blue PL emitting centres, optimum processing conditions in terms of excess Si concentration and overall thermal budget are mandatory. The nature of the observed blue emission is discussed.

Blue and violet photoluminescence from high-dose Si+- and Ge+-implanted silicon dioxide layers

Abstract Strong blue (around 470 nm) and violet (around 395 nm) photoluminescence (PL) at room temperature (RT) was obtained from thermally-grown SiO 2 films on crystalline Si implanted with Si + and Ge + ions, respectively. Photoluminescence excitation (PLE) spectroscopy measurements indicate maximum PL at 248 nm (for Si + ) and 242 nm (for Ge + ). The blue PL intensity was investigated as a function of subsequent furnace and flash lamp annealing. The results obtained are interpreted in terms of the excess atoms introduced in the SiO 2 network.

Effect of ion dose and annealing mode on photoluminescence from SiO2 implanted with Si ions

This paper discusses the photoluminescence spectra of 500-nm-thick layers of SiO2 implanted with Si ions at doses of 1.6×1016, 4×1016, and 1.6×1017 cm−2 and then annealed in the steady-state region (30 min) and pulsed regime (1 s and 20 ms). Structural changes were monitored by high-resolution electron microscopy and Raman scattering. It was found that when the ion dose was decreased from 4×1016 cm−2 to 1.6×1016 cm−2, generation of centers that luminesce weakly in the visible ceased. Moreover, subsequent anneals no longer led to the formation of silicon nanocrystallites or centers that luminesce strongly in the infrared. Annealing after heavy ion doses affected the photoluminescence spectrum in the following ways, depending on the anneal temperature: growth (up to ∼700 °C), quenching (at 800–900 °C), and the appearance of a very intense photoluminescence band near 820 nm (at >900 °C). The last stage corresponds to the appearance of Si nanocrystallites. The dose dependence is explained by a loss of stability brought on by segregation of Si from SiO2 and interactions between the excess Si atoms, which form percolation clusters. At low heating levels, the distinctive features of the anneals originate predominantly with the percolation Si clusters; above ∼700 °C these clusters are converted into amorphous Si-phase nanoprecipitates, which emit no photoluminescence. At temperatures above 900 °C the Si nanocrystallites that form emit in a strong luminescence band because of the quantum-well effect. The difference between the rates of percolation and conversion of the clusters into nanoprecipitates allows the precipitation of Si to be controlled by combinations of these annealings.

Photoluminescence of Si3N4 films implanted with Ge+ and Ar+ ions

The room-temperature photoluminescence emission and excitation spectra of Si3N4 films implanted with Ge+ and Ar+ ions were investigated as a function of the ion dose and temperature of subsequent annealing. It was established that the implantation of bond-forming Ge atoms during annealing right up to temperature Ta=1000 °C stimulates the formation of centers emitting in the green and violet regions of the spectrum. Implantation of inert Ar+ ions introduces predominantly nonradiative defect centers. Comparative analysis of the photoluminescence spectra, Rutherford backscattering data, and Raman scattering spectra shows that the radiative recombination is due not to quantum-well effects in Ge nanocrystals but rather recombination at the defects ≡Si-Si≡, ≡Si-Ge≡, and ≡Ge-Ge≡.