Relaxation of silicon non-equilibrium depletion with majority charge carriers in strong electric fields, its mechanisms and ways to damp it

This overview deals with original works of authors as well as with works by native and foreign authors, which are devoted to this or close topics. It is written with account of the modern state of the problem, to solve which a great amount of successful work was made by Academician of NAS of Ukraine O.V. Snitko. Considered in this paper are the essence of the phenomenon of non-equilibrium depletion with majority charge carriers that takes place in the field effect in silicon and a set of new phenomena that were revealed by the authors when investigating this effect. Besides, analyzed in detail are the processes of acceleration inherent to relaxation of the non-equilibrium depletion in strong electric fields (Es = 3·10³ – 5·10⁵ V/cm) at silicon surface being in various physical-and-chemical states. It is noted that the Franz-Keldysh or Frenkel effects for local centers play the main role in acceleration of relaxation with growing Es at the silicon surface. In this case, an essential role belongs to electron-phonon interaction of the charge carrier at the local center with continuum phonons around this center

Effect of oxidation of catalytically active silicon-based electrodes on water decomposition

In this work, we continue to study the revealed phenomenon of current creation in the electrochemical system with distilled water during its decomposition without any applied external voltage. Investigated are catalytically active (to decompose water) electrodes based on silicon with modified surface (due to lapping, texturing, doping with palladium, creation of silicides) before and after thermooxidizing for 1 hour in dry oxygen at 850 ºC. Also performed are investigations of time dependences for the current between silicon electrodes and counter-electrodes made of Al, Pt, Yb when using the circuit with the external voltage V₀ = ± 9.7 V. Analyzed are the results obtained and prospects for a further study

Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically

We have investigated the current creation accompanied by the water decomposition H₂O → OH + H caused by various catalytically active electrodes with different electrochemical potentials, both without external electric voltage on these electrodes and with the applied voltage V₀ = ±9.7 V. It is found that the current value and its time dependence are essentially influenced by such factors as thermal and natural (in ambient atmosphere) oxidation of electrodes (made of Al, Si, Yb, Ni, Ti, Cr₃Si, and Ni₃Si), changing their relief (texturing, polishing), and the electrolytic deposition of palladium as an impurity on the surface (Ti, Cr₃Si). Changes in the current caused by the above factors are realized as a consequence of changes in both the electron work function inherent to these electrodes and their catalytical activity concerning the water decomposition both in the absence and the presence of the external voltage V₀

Study of diamond-like carbon films doped with transition metals and used as cathodes for current creation in water

Properties of diamond-like carbon films (DLCF) on n-Si substrates used as cathodes in Yb – DLCF (n-Si) water electrochemical system have been studied by current creation with water decomposition H2O → OH⁻ + H⁺ . The current is several times higher after preliminary electrolytic deposition of impurity that contains one of the transition metals (Pd, Pt, Ni, Cr) on DLCF (n-Si) layer, which changes the nature of the catalytic process of water decomposition. The aging effect of DLCF (n-Si) 〈Me〉 was observed after 7- to 25-day metal oxidation in air. It is confirmed the change of the electron work function of CDL (n-Si) 〈Me〉 electrode and the current change between it and the Yb electrode

Photoluminescent films of nanocrystalline silicon doped with metals

Effects of electropositive (Au, Ag, Cu) and electronegative (Al, In) metal impurities are investigated from the viewpoint of photoluminescent and electronic properties of nanocrystalline silicon films prepared by laser ablation when depositing them onto a silicon substrate. Measured are time-resolved photoluminescence e. It was ascertained that only Au could essentially increase intensity and stability of photoluminescence, increase its relaxation time by three orders of magnitude as well as decrease the density of states near the film-substrate boundary. It has been shown that the metal impurities provide an essential effect on photovoltage arising in films of nanocrystalline Si as well as the capture of non-equilibrium electrons by traps both in films themselves and at the substrate boundary

Zn and Mn impurity effect on electron and luminescent properties of porous silicon

Investigated in this work are por-Si/n-Si structures prepared by anodizing silicon in 1 % HF water solution, which was followed by natural aging in air and doping with Zn and Mn impurities. When aging, the oxide film of nanoelements in the above structures is substituted by a silicate one. Measurements of temperature dependencies (100...300 K) describing the capacitance photovoltage behavior caused by intense pulses (∼10²¹ quanta/cm2s) of red or white light enabled us to determine the following values and their changes: the boundary potential for n-Si, distribution of the concentration inherent to boundary electron states in the n-Si forbidden gap, concentration of traps for non-equilibrium holes at the interface por-Si/n-Si and in the por-Si layer. The substitution of the oxide film by the silicate one, the thickness of which can exceed the initial thickness of the oxide film, makes these structures more stable and results in sizable changes of spectral dependencies of the short-time (t < 250 ns) and integrated (t > 250 ns) photoluminescence relaxation components as well as shifts the latter into the shortwave range

Effect of laser radiation on catalytic properties of silicon electrodes covered with a transition metal film and providing water decomposition

Current creation caused by water decomposition Н₂О → ОН+Н has been investigated for the case of an Yb-Si electrode pair after the preliminary covering of Si electrodes with transition metal (Ni, Ti, Cr) films, as well as exposing them to laser radiation. It has been shown that laser radiation, as a rule, increases the efficiency of current creation owing to the improvement of electrode catalytic properties as to water decomposition. We observed also some change in the electron work function for these electrode

Effect of microwave electromagnetic radiation on the structure, photoluminescence and electronic properties of nanocrystalline silicon films on silicon substrate

We studied the effect of microwave electromagnetic radiation on silicon low-dimensional structures. The nanocrystalline silicon (nc-Si) films on p-Si substrate were formed with pulsed laser ablation. The surface morphology of films was studied with atomic force microscopy. We made X-ray phase analysis of films and measured strains in the structures obtained using X-ray diffractometry. We also investigated the time-resolved photoluminescence (PL) spectra and temperature dependence of photovoltage for the nc-Si/p-Si and nc- Si/p-Si structures, both before and after exposure to magnetron microwave radiation of moderate (1.5 W/cm²) irradiance. It was shown that after microwave irradiation photovoltage in the nc-Si films, as well as electron trap concentration in both the films and p-Si substrates, decrease. After irradiation of the nc-Si/p-Si structures the density of interfacial electron states (IES) decreases, while both PL intensity and relaxation time increase. At the same time irradiation of the nc-Si/p-Si structures that had high values of PL intensities and relaxation times before irradiation results in decrease of these values, as well as somewhat increases the density of IES. Higher (7.5 W/cm2) irradiance of microwave field impairs the PL properties (to the point of complete disappearance of PL). In addition it induces changes in film structure resulting, in the course of time, in decrease of strains in the structures studied. We discuss some mechanisms for microwave field effect on the properties of these structures

Electronic properties of silicon surface at different oxide film conditions

We used measurements of temperature and electric field dependencies of surface photovoltage to study electronic properties of (100) n-silicon surface after its thermal and chemical oxidation, as well as after oxide films removal in HF. Measurements of surface photovoltage vs temperature curves revealed two peaks of the fast surface electron states (SES) density. They lie in the gap in the region of Pb₀₋ and Pb₁₋centers manifestation. The parameters of SES systems that were determined from the surface photovoltage vs electric field curves differ substantially from those determined from the temperature dependencies of surface photovoltage. They depend on the silicon surface condition, material resistivity and temperature at which the measurements were made. This is because the SES systems in oxide films (that exchange electrons with silicon via transport mechanisms) affect the measurements of electric field dependence of surface photovoltage. Remove selecte