Co-implantation Of Si Research Articles

Optical characterizations of doped silicon nanocrystals grown by co-implantation of Si and dopants in SiO2

Co-implantation, with overlapping implantation projected ranges, of Si and doping species (P, As, and B) followed by a thermal annealing step is a viable route to form doped Si nanocrystals (NCs) embedded in silica (SiO2). In this paper, we investigate optical characterizations of both doped and un-doped Si-NCs prepared by this method. The effective NC presence in the oxide layer and their crystallinity is verified by Raman spectrometry. Photoluminescence (PL) and PL excitation measurements reveal quantum confinement effects and a gradual PL quenching with increasing dopant concentrations. In un-doped NC, the measured Stokes shift remains constant and its value ∼0.2 eV is almost twice the Si–O vibration energy. This suggests that a possible radiative recombination path is a fundamental transition assisted by a local phonon. PL lifetime investigations show that PL time-decays follow a stretched exponential. Using a statistical model for luminescence quenching, a typical NC diameter close to 2 nm is obtained for As- and P-doped samples, consistent with our previous atomic probe tomography (APT) analyses. APT also demonstrated that n-type dopant (P and As) are efficiently introduced in the NC core, whereas p-type dopant (B) are located at the NC/SiO2 interface. This last observation could explain the failure of the luminescence-quenching model to determine NC size in B-doped samples. All together, these experimental observations question on possible different carrier recombination paths in P or As doped NC compared to B one's.

Inhibitive formation of nanocavities by introduction of Si atoms in Ge nanocrystals produced by ion implantation

Germanium nanocrystals (Ge-nc) were successfully synthesized by co-implantation of Si and Ge ions into a SiO2 film thermally grown on (100) Si substrate and fused silica (pure SiO2), respectively, followed by subsequent annealing at 1150 °C for 1 h. Transmission electron microscopy (TEM) examinations show that nanocavities only exist in the fused silica sample but not in the SiO2 film on a Si substrate. From the analysis of the high-resolution TEM images and electron energy-loss spectroscopy spectra, it is revealed that the absence of nanocavities in the SiO2 film/Si substrate is attributed to the presence of Si atoms inside the formed Ge-nc. Because the energy of Si-Ge bonds (301 kJ·mol−1) are greater than that of Ge-Ge bonds (264 kJ·mol−1), the introduction of the Si-Ge bonds inside the Ge-nc can inhibit the diffusion of Ge from the Ge-nc during the annealing process. However, for the fused silica sample, no crystalline Si-Ge bonds are detected within the Ge-nc, where strong Ge outdiffusion effects produce a great number of nanocavities. Our results can shed light on the formation mechanism of nanocavities and provide a good way to avoid nanocavities during the process of ion implantation.

Control of the Ge nanocrystal synthesis by co-implantation of Si+

The synthesis of Ge nanocrystals (Ge-nc) prepared by 74Ge+ implantation into fused silica followed by co-implantation of Si+ has been investigated for annealing temperatures varying between 850 and 1150 °C. By limiting the thermal diffusion of Ge, co-implanting Si reduces the Ge desorption and affects the growth of Ge-nc, through a Ge trapping mechanism involving the formation of Ge-Si chemical bonds. This is supported by Raman analysis, providing information regarding the material composition for a large variety of fabrication parameters, as well as high resolution scanning electron microscopy imaging, indicating that the average dimension of the synthesized Ge-nc decreases for increasing doses of co-implanted Si. From the spectral analysis of Raman measurements, a systematic evolution of the Ge-Ge, Ge-Si, and Si-Si bond concentrations is characterized as a function of the co-implantation fluences. Two different regimes are clearly identified for each annealing temperature. The first is associated with a linear increase of the residual Ge content with respect to the co-implanted Si, having a slope of ∼1, independent of the annealing temperature. Here, the nucleation of pure Ge-nc and Ge-nc containing Si impurities occurs at similar rates, for co-implanted Si fluences generally lower than the dose of implanted Ge. The second regime occurs for greater co-implantation fluence thresholds that depend on the annealing temperature. It is related to the saturation of the Ge trapping efficiency. In this regime, the formation of Si-Ge bonds dominates, sufficiently reducing the diffusion of Ge to prevent the formation of pure Ge-nc. In addition to limiting the unwanted and critical Ge desorption effects, Si co-implantation is a promising technique for precisely controlling the Ge-nc density, diameter, and uniformity at nanoscale dimensions, parameters which cannot be solely set from the local Ge concentration and/or the annealing parameters due to the high thermal diffusivity of Ge.

Enhanced photoluminescence from Si + and C + ions co-implanted porous silicon formed by electrochemical anodization

Enhanced photoluminescence (PL) was obtained from electrochemically formed porous silicon (PS) on crystalline silicon wafer with co-implantation of Si + and C + ions. It is demonstrated that PS formation can preferentially be initiated during electrochemical anodization process for ion implanted samples, as shown from the scanning electron microscopy (SEM) characterization and current density versus etching duration ( J – t ) plots during anodization process. For the PS sample with co-implantation of Si + and C + ions, SiC (or amorphous Si 1− x C x ) nanostructures are embedded in the SiO 2 matrix after high-temperature annealing, as indicated from X-ray Photoelectron spectroscopy (XPS) characterization. The enhanced photoluminescence (PL) emission from the PS sample with co-implantation of Si + and C + ions is attributed to the enhanced formation of PS induced by ion implantation. Meanwhile, the appearing of SiC (or amorphous Si 1− x C x ) nanostructures with localized recombination of optically excited holes and electrons in the SiO 2 matrix, also contributes to the enhanced PL emission. Porous silicon with co-implantation of Si + and C + ions shows promising perspective for applications in Si-based optoelectronics.

Ion-implantation technology for improved GaAs MESFETs performance

Electrical properties of Si-implanted and co-implanted with Mg or Be in semi-insulating GaAs was studied. The Si-implanted MESFETs with and without buried p-layer (formed by Mg or Be) have been fabricated and characterized by their d.c. and r.f. performance. The experimental results showed that the device with a buried p-layer can effectively suppress the substrate leakage current (thus good pinch-off characteristic) and obtained higher gain linearity than these without a buried p-layer. For 1 μm×100 μm MESFETs device with co-implantation of Si (∼8×1012 cm−2) and Be (∼6×1011 cm−2) demonstrated uniform transconductance (gm) of ∼115 mS mm−1 with the gate voltage ranging from −1 to 1 V and reduced pinch-off voltage compared to those with co-implantation of Si and Mg (∼6×1011 cm−2). The measured fT and fmax of a 1 μm×25 μm MESFET with co-implantation of Si and Be are 10 and 39 GHz, respectively. However, FETs with increased Mg dose (from 6×1011 cm−2 to 2×1012 cm−2) in a buried p-layer can obtain higher transconductance and saturation current.

Co-implantation of Si+N into GaN for n-type doping

Si-doping characteristics have been systematically investigated for Si+N co-implanted GaN. n-type regions were produced in undoped GaN films by the co-implantation and subsequent annealing with an SiO2 encapsulation layer at high temperatures. The sheet carrier concentration is seen to be precisely controllable between 3×1012 and 5×1014 cm−2 with Si activation efficiencies of ∼50% when the samples were annealed at 1300 °C. From atomic force microscopic observations, the co-implanted sample shows smooth surface morphology identical to that before implantation, whereas Ga islands are found to be formed in the surface region by the activation annealing in the case of conventional Si implantation. Therefore, the Si+N co-implantation technique turns out to be an effective method to enhance electrical and structural properties in view of GaN stoichiometry. However, implantation-induced microdefects seem to remain even after the high-temperature annealing process for both Si- and Si+N-implanted GaN samples.

CO-implantation of Si and Be in SI GaAs for improved device performance

The effect of co-implantation of Si and Be in GaAs is discussed in the light of tailoring of a MESFET implantation profile. The modified profile is calculated by considering electrical activation and diffusion of both Si and Be in GaAs. The results compare well with a realized n-layer measured by the C– V technique. Since the pinch-off voltage is a figure of merit of device performance, a calculation of the latter using a tailored implantation profile is also presented in this paper.

Residual post anneal damage of Ge and C co-implantation of Si determined by quantitative RBS-channelling

A (100) silicon wafer was implanted with 150 keV 1.6×10 15 Ge +/cm 2 to produce 175 nm amorphous silicon followed by 65 keV carbon implants ( R p =175 nm) with various doses. After regrowth at 1000°C for 15 s the dechannelling due to residual defects was studied as a function of the carbon dose by accurate RBS-channelling and the data were analysed using the DICADA code and Transmission Electron Microscopy (TEM) measurements of dislocation loop densities. The present study reveals that the presence of carbon influences not only the End-of-Range (EoR) dislocation loops formed below the original amorphous/crystalline interface but also the randomly distributed point defects. The presence of carbon in both the top amorphised and regrown layer as well as the underlying substrate causes a reduction in the point defect density of 85% for the highest carbon dose of 1×10 15 C +/cm 2.

MeV ion implantation in GaAs technology

The technology base of MeV ion implantation in GaAs is reviewed, n-type implantation using Si and Si and S co-implants is emphasized. Experimental range and shape parameters obtained using secondary ion mass spectroscopy (SIMS) of Si implants having energies from 1 to 20 MeV are presented. Activation studies of these implants, as well as Si and S co-implants, annealed using both furnace anneal and rapid thermal anneal have been performed with Hall and capacitance-voltage measurements. Buried n + profiles with a peak carrier concentration of 2 × 10 18/cm 3, located as deep as 6 μm beneath the surface have been formed with the co-implantation of Si and S. Application of these implants to GaAs device fabrication is discussed. Several techniques for masking the high energy implants during selective implantation are presented. The performance values of two demonstration devices, a mixer diode and a varactor diode, show that state-of-the-art devices can be fabricated using MeV implantation.

Effects of coimplantation of silicon and nitrogen on structural defects and Si-N bond formation in silica glass.

Effects of coimplantation of Si and N ions on structural defects in ${\mathrm{SiO}}_{2}$ glass are reported. Silicon-silicon bonds are formed as the predominant defect and their concentrations are almost the same as those of the implanted ions in Si-implanted samples but only about 1/10 those in the case of N-implanted samples. The bond concentrations in the coimplanted samples are approximately 50% of the sum of the concentrations in samples implanted with either Si or N. No difference was observed in the concentrations between specimens coimplanted in two different sequences. Paramagnetic nitrogen dioxide molecules are found to be formed in N-implanted samples but are not detected in the coimplanted samples. These results show that coimplantation is highly effective in combining implanted silicon with nitrogen, resulting in the formation of Si-N bonds. The importance of a Si-Si bond is suggested as an active reaction intermediate in coimplantation in ${\mathrm{SiO}}_{2}$.

Co-Implantation of Si And Be in GaAs by Rapid Thermal Annealing

ABSTRACTA buried p-layer in GaAs MESFET channel is successfully formed by (Si,Be) co-implantation and rapid thermal annealing process. The annealing cycle is optimized to activate Si and Be simultaneously and to minimize the dopant redistribution for precise dopant control. As a result, more than 80% activation efficiency for both Si and Be, as well as the greatly improved doping abruptness from 85 nm/decade to 65 nm/decade are achieved. Devices are fabricated and superior performance including sharper pinchoff, an increase of RF gain by 2–3dB and a 40% decrease in backgating effect is observed.