E. I. Terukov

Room‐temperature photoluminescence of erbium‐doped hydrogenated amorphous silicon

A comparison of the photoluminescence of Er‐doped hydrogenated amorphous silicon and crystalline silicon a‐Si:H(Er) and c‐Si(Er), is presented. It is shown that a‐Si:H(Er) exhibits efficient room‐temperature photoluminescence at 1.537 μm which is as strong as the emission from optimized c‐Si(Er) at 2 K. Most remarkably, there is practically no temperature quenching of the emission intensity in the range 2–300 K. The experiments suggest that the lifetime connected with the Er‐induced emission is considerably shorter in a‐Si:H(Er) than in c‐Si(Er) which may be responsible for the different dependences of the photoluminescence intensity on the temperature, chopping frequency, and excitation power.

Resonant nonradiative energy transfer to erbium ions in amorphous hydrogenated silicon

The simultaneous study of absorption, luminescence, and ODMR spectra of erbium doped a-Si:H and a SiCx:H alloy reveals that Er3+ ions are pumped by a resonant but nonradiative energy transfer from electron–hole pairs excited in the host. Direct optical pumping into absorption lines of Er3+ is not observed. The emission of the Er3+ ions is strong and decreases only moderately from 77 K to room temperature. We propose an energy transfer by a Forster mechanism, based on resonant dipole coupling, which quenches efficiently the luminescence of the host in the case of large erbium concentration. Resonance of electron–hole pairs to the excited state of the rare earth ion is achieved as electrons thermalize in tail states.

Local environment of erbium atoms in amorphous hydrogenated silicon

The 169Er(169Tm)emission Mossbauer spectroscopy has evidenced that photoluminescence centers in Er-doped amorphous hydrogenated silicon are [Er–O] clusters. The local environment of the Er3+ ions in the clusters is similar to the Er3+ environment in Er2O3.

Room-temperature electroluminescence of erbium-doped amorphous hydrogenated silicon

We have observed strong room-temperature electroluminescence at 1.54 μm induced by erbium ions in amorphous hydrogenated silicon (a-Si:H). The device consisted of an Al/a-Si:H(Er)/n-c-Si/Al structure. A mechanism for electronic excitation of the erbium ions in the amorphous matrix is proposed that is based on defect-related Auger excitation.

Observation by conductive-probe atomic force microscopy of strongly inverted surface layers at the hydrogenated amorphous silicon/crystalline silicon heterojunctions

Heterojunctions made of hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) are examined by conducting probe atomic force microscopy. Conductive channels at both (n)a-Si:H/(p)c-Si and (p)a-Si:H/(n)c-Si interfaces are clearly revealed. These are attributed to two-dimension electron and hole gases due to strong inversion layers at the c-Si surface in agreement with previous planar conductance measurements. The presence of a hole gas in (p)a-Si:H/(n)c-Si structures implies a quite large valence band offset (EVc-Si−EVa-Si:H>0.25 eV).

Lithium intercalation into amorphous-silicon thin films: An electrochemical-impedance study

Lithium intercalation into 0.25-μm-thick films of amorphous silicon is studied using the electrochemical-impedance technique. An equivalent circuit, proposed for such electrodes, comprises the electrolyte resistance and three units connected in series, each unit being a parallel combination of a resistance and a constant-phase element. The units relate to the charge transfer processes at the silicon/electrolyte interface, charge transfer though the passive film on the silicon, and the lithium diffusion into the silicon bulk. During potential cycling, changes occur largely in the unit related to the passive film. The lithium diffusion coefficient in the amorphous silicon is estimated as ∼ 10−13 cm2 s−1.

Photoconductivity of two-phase hydrogenated silicon films

Electrical, photoelectric, and optical properties of hydrogenated amorphous silicon films with various ratios between the nanocrystalline and amorphous phases in the structure of the material have been studied. On passing from an amorphous to a nanocrystalline structure, the room-temperature conductivity of the films increases by more than five orders of magnitude. With increasing fraction of the nanocrystalline component in the film structure, the steady-state photoconductivity varies nonmonotonically and is determined by the variation in the carrier mobility and lifetime. Introduction of a small fraction of nanocrystals into the amorphous matrix leads to a decrease in the absorption in the defect-related part of the spectrum and, accordingly, to a lower concentration of dangling bonds, which are the main recombination centers in amorphous hydrogenated silicon. At the same time, the photoconductivity in these films becomes lower, which may be due to appearance of new centers that are related to nanocrystals and reduce the lifetime of nonequilibrium carriers.

Time-resolved photoluminescence of erbium centers in amorphous hydrogenated silicon

Abstract A time-resolved photoluminescence (PL) technique is employed to study the mechanisms of excitation and de-excitation of Er 3+ ions in amorphous hydrogenated silicon (a-Si:H) at temperatures 5–300 K. The PL at 1.5 μm is found to arise within times shorter than a 100 ns after irradiation with a nanosecond laser pulse, indicating a fast energy transfer from the electronic excitation of a-Si:H to the Er 3+ ions. The PL transients exhibit a stretched exponential decay with mean lifetime ranging from 20 to 35 μs when the temperature decreases from 300 K down to 5 K. The experimental results support the model of defect-related excitation and de-excitation of the Er 3+ ions.

Pulsed ion-beam synthesis of β-FeSi2 precipitate layers in Si(100)

Semiconducting iron disilicide (?-FeSi2) precipitate layers were synthesized by means of Fe+ implantation into Si(100) at an energy of 40?keV and a dose of 1?1016?cm-2 followed by nanosecond pulsed ion-beam treatment of the implanted Si layers. Glancing incidence x-ray diffraction (GIXRD) and atomic force microscopy (AFM) were employed for the structural characterization, and optical absorption and photoluminescence (PL) spectroscopies were used for the optical characterization of the precipitate layers formed. The GIXRD results indicate the formation of oriented ?-FeSi2 precipitates surrounded by a polycrystalline Si matrix. AFM data show the precipitate sizes to be in the range of 25-90?nm. The results of measuring the optical absorption indicate that the formed precipitates have a direct-band structure with an energy gap of 0.83?eV. It is shown that the 1.5 ?m PL signal of ?-FeSi2 precipitates is observed up to a temperature of 210?K and does not saturate up to the pump power of 250?mW.

Energy transfer between silicon nanocrystals

It is shown that the energy migration between silicon nanocrystals embedded into a silicon dioxide host is caused by the “nonresonant” dipole-dipole interaction. This process is efficient only for a part of small nanocrystals among the whole ensemble of nanocrystals. The nonresonant dipole-dipole energy transfer has such a feature as the emission of two optical phonons at each step of the process. The time of the excitation transfer has been experimentally determined for nanocrystals 1.5 nm in size existing in the ensemble of nanocrystals with a density of 1018 cm−3 and the size distribution with a standard deviation of 20%. A value of 30 μs obtained for this time is in good agreement with the performed theoretical estimation.