SiH Complexes Research Articles

OH-Si complex in hydrogenated n-typeβ-Ga2O3:Si

Si is an n-type dopant in Ga2O3 that can be intentionally or unintentionally introduced. The results of Secondary Ion Mass Spectrometry, Hall effect, and infrared absorption experiments show that the hydrogen plasma exposure of Si-doped Ga2O3 leads to the formation of complexes containing Si and H and the passivation of n-type conductivity. The Si-H (D) complex gives rise to an O-H (D) vibrational line at 3477.6 (2577.8) cm−1 and is shown to contain a single H (or D) atom. The direction of the transition moment of this defect has been investigated to provide structure-sensitive information. Theory suggests possible structures for an OH-Si complex that is consistent with its observed vibrational properties.

Effect of etching time in hydrofluoric acid on the structure and morphology of n-type porous silicon

We studied the influence of etching time in hydrofluoric acid and methanol solution on the structure and morphology of n-type porous silicon (PSi). Dissolution of Si in the solution of hydrofluoric acid with methanol with surface oxidation occurs. All investigated samples reveal pores with increasing average size proportional to the etching time. Areic density and RMS roughness observed by scanning electron and atomic force microscopies have maximum for 10 min etching time. Additional etching time leads to slight increase in the pore size diameter and decreasing the RMS roughness of layers. All amorphous PSi samples are covered with the SiO2 layer containing probably HySiOx and SiFxHy complexes. The presence of SiH complexes leads probably to the growth of PSi layers with pores. The thickness of this layer depends on etching time and probably contains HySiOx and SiFxOy complexes.

Diffusion and reaction kinetics governing surface blistering in radio frequency sputtered hydrogenated a-SixGe1-x (0 ≤ x ≤ 1) thin films

The preparation of blister free layers of hydrogenated a-SixGe1-x (0 ≤ x ≤ 1) is a primary requisite for their technological applications. In RF (Radio Frequency) sputtered layers the formation of blisters is temperature dependent, as also shown here. This dependence is used to propose a theoretical model aimed at a better understanding of the mechanisms determining the blistering. Beside the reaction kinetics responsible for the release of H atoms from SiH and/or GeH complexes the model takes into particular account the contribution of the diffusion of H. The activation energy for blistering also enters in the model. The validation of the theoretical frame of the model is confirmed by the fact that it predicts a blistering threshold temperature in reasonable agreement with the experiment. The amorphous hydrogenated thin layers were deposited on polished silicon by RF co-sputtering. They were annealed between 150 and 350 °C. The structural changes of the surface of the SiGe films have been explored systematically by light beam reflection, scanning electron microscopy while the depth distribution of hydrogen was measured by secondary neutral mass spectrometry.

Perovskites: Between the Grains

Defect reduction and device stabilization will continue to be two important thrusts toward efficient long-lasting polycrystalline perovskite solar cells. Recently in Chem, Zong et al. show that a complementary hydrophobic/hydrophilic triblock copolymer continuously incorporates into methylammonium lead tri-iodide grain boundaries. This improves solar cell stability and performance, resulting in a stabilized 19.4% power conversion efficiency, 92% of which is retained after 480 hr of continuous 1-sun illumination.

Hydrogen passivation of polycrystalline silicon thin films

The influence of post-hydrogenation on the electrical and optical properties of solid phase crystallized polycrystalline silicon (poly-Si) was examined. The passivation of grain-boundary defects was measured as a function of the passivation time. The silicon dangling-bond concentration decreases with increasing passivation time due to the formation of Si-H complexes. In addition, large H-stabilized platelet-like clusters are generated. The influence of H on the electrical properties was investigated using temperature dependent conductivity and Hall-effect measurements. For poly-Si on Corning glass, the dark conductivity decreases upon hydrogenation, while it increases when the samples are fabricated on silicon-nitride covered Borofloat glass. Hall-effect measurements reveal that for poly-Si on Corning glass the hole concentration and the mobility decrease upon post-hydrogenation, while a pronounced increase is observed for poly-Si on silicon-nitride covered Borofloat glass. This indicates the formation of localized states in the band gap, which is supported by sub band-gap absorption measurments. The results are discussed in terms of hydrogen-induced defect passivation and generation mechanisms.

Reconfiguration and dissociation of bonded hydrogen in silicon by energetic ions

We report in situ infrared measurements of ion-induced reconfiguration and dissociation of bonded hydrogen associated with various defects in silicon at low temperatures. Defect-associated Si-H complexes were prepared by low-temperature proton implantation in silicon followed by room-temperature annealing. As a result of subsequent low-temperature $^{3}\mathrm{He}$ ion irradiation, we observed (1) ion-induced dissociation of Si-H complexes, (2) a notable difference in the dissociation rate of interstitial- and vacancy-type defects, and, unexpectedly, (3) the growth of bond-centered hydrogen, which is generally observed in association with low-temperature proton implantation. These findings provide insight into the mechanisms responsible for the dissociation of hydrogen bonds in silicon and thus have important implications for bond-selective nanoscale engineering and the long-term reliability of state-of-the-art silicon semiconductor and photovoltaic devices.

Density functional simulations of silicon-containing point defects in diamond

Silicon impurities in diamond lead to the appearance of the well known system of 12 lines around $1.681\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, thought to arise from the silicon-vacancy complex. This system is produced by various treatments suggestive of other silicon-related centers in the material. In order to elucidate possible structures of Si in diamond, we have performed first-principles calculations. We show that interstitial Si is unstable at growth temperatures, substitutional Si is most likely visible only by vibrational mode spectroscopy, and complexes of silicon with lattice vacancies are electrically, paramagnetically, and optically active. In addition, we report on Si-N and Si-H complexes in the context of doping and the KUL3 electron paramagnetic resonance center, respectively.

Optical and electrical properties of thin wafers fabricated from nanocrystalline silicon powder

The infrared transmittance spectra and dark conductivity of wafers fabricated from nanocrystalline silicon powder (nc-Si) have been studied. The initial nc-Si powder is first synthesized by laser-induced silane dissociation, with the temperature of the surrounding buffer gas varied from 20 to 250°C, and then compacted at pressures from 108 to 109 Pa. It is found that compaction of the nc-Si powder results in formation of Si-H, Si-CHx, and Oy-Si-Hx structures (x, y=1–3). The formed structures break down under annealing, with the Si-H and Si-CHx complexes disintegrating at the lowest annealing temperature (t = 160°C). The dark conductivityof the nc-Si wafers is shown to increase along with the buffer gas temperature at which the starting powder was prepared. Two temperature regions are found in which the dark conductivity behaves in radically different ways. At wafer temperatures T ≥ 270 K, conductivity is mediated by free carriers, whereas, at lower temperatures, electron transport is governed by hopping conduction over localized states in the band gap.

Electron-beam-induced reactivation of Si dopants in hydrogenated two-dimensional AlGaAsheterostructures: a possible new route for III–V nanostructure fabrication

Hydrogen incorporation in n-type Si-doped GaAs epilayers is a well-known process whichleads to the neutralization of the active Si impurities with the formation of SiH complexes.Recently, we have shown that SiH complex dissociation and, consequently, Si-dopantreactivation could occur when the epilayers are exposed to an electron beam.Two epilayers have been studied: the first is a0.35 µm thick hydrogenated Si-doped GaAs epilayer and the second is Si planar-dopedAlGaAs/GaAs/InGaAs heterostructures.Firstly, Hall effect measurements have been carried out on the epilayers exposed, after RFhydrogen plasma exposition, to increasing electron doses with different injectionenergies. For the 2D heterostructures, we have observed that the free carrier densityNs does notvary significantly for weak electron densities. This reactivation presents a threshold value, contrary to the0.35 µm epilayerin which Ns varies quite linearly. It will be shown that such phenomena might be attributed to thefilling of surface states as the dopants are progressively reactivated.Then, using a high spatial resolution electron beam lithography system, nanometricconductive patterns have been fabricated starting from hydrogenated epilayers. Electricmeasurements have been performed and the results obtained show that about 15 nm spatialresolution could be expected.In conclusion, taking into account this spatial resolution, the high spatial contrast ofconductivity which could be expected due to the existence of an electron dosethreshold, and the high mobility of the AlGaAs/GaAs/InGaAs heterostructure,the effects described in this paper could open a new way for the fabrication ofIII–V 1D or 2D mesoscopic structures for electronic or optoelectronic applications.

Electron-beam-induced reactivation of Si dopants in hydrogenated and deuterated 2D AlGaAs heterostructures. Application to the fabrication of nanostructures

AbstractHydrogen incorporation in n-type Si-doped GaAs epilayers is now a well-known process. This paper is devoted to the study of the stability of SiH (SiD) complexes when submitted to an electron beam in n-type Si-doped GaAs epilayer and also in 2D-AlGaAs heterostructures exposed to a hydrogen or deuterium plasma.The results obtained by Hall effect measurements on hydrogenated and deuterated GaAs epilayers with different thicknesses (0.2 and 0.35νm) and Si planar-doped AlGaAs/GaAs/InGaAs heterostructures exposed to an electron beam with different injection energies (10 to 50 keV) are presented. On one hand, the reactivation of Si dopants strongly decreases when deuterium is used. On the other hand, the study of this reactivation versus injection energies of electrons suggests an energetic electron excitation effect rather than a minority carrier generation effect. In addition, for the 0.2νm thick GaAs epilayer and the 2D heterostructures, the free carrier density does not vary significantly for low electron densities, and as a consequence, the reactivation of the Si dopants occurs above an electron dose threshold. This phenomenon might be attributed to the filling of surface states as the dopants are progressively reactivated.As a result, due to the electron dose threshold as well as their high electron mobility properties, Si planar-doped AlGaAs/GaAs/InGaAs heterostructures are particularly interesting to reactivate dopants, with a good spatial contrast, using an electron beam irradiation and the effects described in this paper could open the fabrication of high mobility 1D or 2D mesoscopic structures for electronic or optoelectronic applications.

Electron-induced dissociation of SiH complexes in hydrogenated Si-doped GaAs. Application to the fabrication of microstructures

We study the role of hot electron injection in the dissociation of the SiH complexes which appear in n-type Si-doped GaAs epilayer exposed to a hydrogen or deuterium plasma. Firstly, the results recently obtained in room-temperature aging experiments on hydrogenated or deuterated Schottky diodes submitted to high bias voltage are summarized and the role of hot carriers in the dissociation of donors and the observed isotope effect are described. Then, it is shown that SiH dissociation can also be achieved using hot carriers injected into the semiconductor by electron beam. Such electron-beam effects are finally used for the fabrication and characterization by cathodoluminescence of micronic conductive GaAs structures.

Staebler-Wronski effect as a function of the Fermi level position and structure of nondoped, amorphous, hydrated silicon

The photoconductivity degradation rates γ (σph∼t−γ) of nondoped, amorphous, hydrated silicon films deposited at Ts=300–400 °C and subjected to illumination for 5 h at 300 K (light source 100 mW/cm2, λ<0.9 µm) were investigated. It was shown that the degradation rate γ depends on the preillumination position of the Fermi level ɛc−ɛF and often is not directly related to the hydrogen content in the film. It was found that there are correlations between the value of γ and the bonds in the silicon-hydrogen subsystem [isolated SiH and SiH2 complexes, clusters (SiH)n, and chains (SiH2)n].

AB-INITIO STUDIES OF DIFFUSION AND GROWTH PHENOMENA ON SEMICONDUCTOR SURFACES

We discuss the application of ab-initio quantum-mechanical calculations, based on pseudopotential local-density-functional theory, to diffusion and growth phenomena on semiconductor surfaces. We examine in detail two specific examples: adatom diffusion on the Ge (111) c (2×8) reconstructed surface and surfactant-mediated homoepitaxial growth on Si substrates. In these examples, the combination of results from first-principles calculations and simple simulations helps elucidate complex dynamical phenomena. We also make predictions on the feasibility of using hydrogen as a surfactant on Si substrates, by drawing analogies between the chemical behavior of group-V or group-VI adsorbates and Si-H complexes.

Modelling of hydrogen centres in silicon and its oxides by Muon implantation

A study has been carried out of the hydrogen sites in amorphous silicon a-Si, a-Si:H and its monoxide a-SiO using the technique of MuSR. The existence of H at the tetrahedral interstitial and bond-centre sites have been confirmed by the identification of the analogous centres Mu′ and Mu ∗. However, the larger fraction of hydrogen prefers the formation of the Si-H complex. The Mu ∗ state appears to survive to higher temperatures than in c-Si.

Temperature dependence of the vibrations of the Si-H complex in GaAs and AlAs.

The temperature dependences between T=5.5 and 300 K of the vibrational absorption of hydrogen-plasma-exposed Si-doped AlAs and GaAs epilayers are presented. The vibrational absorption of the AlAs:Si-H and GaAs:Si-H layers was investigated using high-resolution Fourier-transform spectroscopy. While the bend mode vibration of the Si-H complex was found to have a similar energy in both materials, the stretch mode vibration occurred at a lower energy for the ${\mathrm{Si}}_{\mathrm{Al}}$-H complex. The temperature dependence of the bend and stretch mode line shifts and linewidths are found to be described by a model based on phonon emission and the dephasing relaxation of the vibrations. The broadening of the stretch mode absorption is very rapid and follows a temperature dependence of the form \ensuremath{\sim}${\mathit{e}}_{\mathit{a}}^{\mathrm{\ensuremath{-}}\mathit{E}}$/kT. The small activation energy ${\mathit{E}}_{\mathit{a}}$ of \ensuremath{\sim}9 meV suggests that the linewidth broadening is due to elastic scattering by localized low-energy acoustic phonons.

Thermal dissociation energy of the Si-H complex in n-type GaAs

The thermal dissociation kinetics of the hydrogen-donor complex in n-type GaAs:Si were determined from bias-temperature anneals on hydrogenated Schottky-barrier diodes. The anneal kinetics are approximately first order and yield a thermal dissociation energy for the Si-H complex of 1.2±0.1 eV. Depth redistribution of the Si-H complexes both within the depletion layer of biased diodes and in the field-free region of unbiased diodes suggests that hydrogen in n-type GaAs can migrate as a negatively charged species.

Hydrogen solubility in n-type silicon doped GaAs and its effects on the material electronic quality

Solubility of hydrogen in silicon doped GaAs has been investigated from deuterium diffusion experiments in buried silicon doped GaAs epilayers exposed to a deuterium plasma. The presence of silicon donors in the buried layer induces an increase of the solubility of hydrogen equal to the amount of active donors. Diffusion profiles after thermal annealing provide evidence that, in the buried doped layer, hydrogen is present at least in two forms: a mobile species, which is removed under annealing at 250 °C, 20 min, and a trapped form known to be Si-H complexes from infrared spectroscopic studies. The electron mobility of the annealed neutralized samples is systematically higher than in as-grown samples, for a given active donor concentration. For plasma conditions used for the fabrication of field effect transistors having a hydrogen neutralized active region, this holds true for buried layers protected by undoped GaAs cap layers as thin as 0.1 μm, then, the defects generated by the plasma are confined on a superficial layer less than 1000 Å.

Photon-Stimulated Desorption of H+ Ions from Oxidized Si(111) Surfaces

Photon-stimulated desorption (PSD) experiments on oxidized Si(111) surfaces were performed to study the adsorption of hydrogen at the SiO2/Si(111) interface using synchrotron radiation. H+ is found to be the only ion product desorbing in significant quantities from the oxidized surfaces at photon energies above 20 eV. PSD spectra of H+ ions, i.e., the H+ ion desorption yield as a function of photon energy, exhibit two peaks at 23 eV and 33 eV. These peaks are interpreted in terms of Si-H bond and O-H bond breaking in a Si-H and Si-OH complex, respectively. The observed dependence of the H+ ion yield on oxidation temperature implies that the peak at 23 eV originates from hydrogen atoms adsorbed onto the so-called Pb centers at the SiO2/Si(111) interface. A comparison between the PSD and the total photoelectric yield spectra, the latter of which corresponds to the photoabsorption spectrum, is also made.

Rheed Observations of Silicon (100) Surface Reconstruction after Remote Hydrogen Plasma Cleaning

ABSTRACTLow temperature silicon epitaxy is critical to novel silicon-based devices requiring hyper-abrupt transitions in doping profiles or heterointerfaces. Epitaxy by Remote Plasma-Enhanced Chemical Vapor Deposition (RPCVD) consists of an in situ remote hydrogen plasma clean of the silicon surface followed by growth of silicon from silane at 220° - 400°C. Reconstruction of the silicon (100) surface from a (1×1) to a (2×1) structure after cleaning at 310°C is observed by RHEED, indicating an atomically clean surface. The removal of carbon and oxygen has been further substantiated by Auger Electron Spectroscopy (AES) and growth on these atomically clean substrates has produced good quality epitaxial films. Using remote hydrogen plasma cleans at lower temperature we report the first observation of third-order silicon surface reconstruction on a Si(100) surface, where two faint fractional order streaks between the sharp integral order streaks are observed. After a short (5 minute), low temperature (300-400 °C) anneal the third order pattern transforms rather quickly to a strong (2×1) reconstruction pattern. The third order pattern can then be restored by following the anneal with a repeat of the lower temperature hydrogen clean. Although the origin of the third order pattern is unclear at this time, we believe it is due to a Si-H complex formation at the silicon surface.

High Quality Deposition of SiO2 Downstream from a Microwave Discharge

ABSTRACTHigh quality stoichiometric silicon dioxide films have been deposited on silicon substrates at low pressure(1.0Torr) and low temperatures(≤ 350C) downstream and at a right angle to a microwave discharge. The deposition was accomplished by injecting 2% SiH4 in helium downstream of a N20 microwave generated discharge. Infrared spectroscopic analysis has determined that no detectable SiH, SiOH, Si-H2o or SiN chemical complexes were present in any films deposited at temperatures above 250C. Rutherford Backscattering and Forward Scattering Detection Spectroscopy were used to determine the elemental composition and hydrogen concentration in the films, respectively. The thick films were found to be stoichiometric with no detectable elemental impurities. The measured hydrogen concentration in the thin films was comparable to that measured in thermally grown Si0 2 of approximately the same thickness. The quality of the thin oxides(&lt;30nm) has been determined by fabricating MOS devices from the Si-Si0 2 system.