V. P. Kuznetsov

Effect of Space Charge Region Width on Er-Related Luminescence in Reverse Biased Si:Er-Based Light Emitting Diodes

In this paper, an effect of space charge region (SCR) width on Er-related electroluminescence (EL) in reverse biased Si:Er-based light-emitting diodes (LEDs) is under investigation. It is concluded that a trivial widening of the SCR in the examined LEDs with triangular and trapezoidal electric field profiles through SCR does not result in a desirable increase in the Er-related EL intensity. The tunnel transit-time diode structure with a complicated electric field profile through SCR is offered to increase the Er-related EL intensity. The difficulties hampering this process in erbium EL from reverse biased LEDs are under discussion

Sublimation molecular beam epitaxy of silicon-based structures

The capabilities of various methods for fabricating silicon-based single-crystal structures are analyzed. The features and advantages of sublimation molecular-beam epitaxy are discussed.

Er3+ photoluminescence excitation spectra in erbium-doped epitaxial silicon structures

Excitation spectra of erbium photoluminescence (λ=1540 nm) in Si: Er epitaxial structures were studied within a broad pump wavelength range (λ=780–1500 nm). Erbium photoluminescence was observed to occur at pump energies substantially less than the silicon band-gap width. Possible mechanisms of erbium ion excitation in this pump radiation energy region are discussed.

Electrically active centers in Si:Er light-emitting layers grown by sublimation molecular-beam epitaxy

Electrically active centers in light-emitting Si:Er layers grown by sublimation molecular-beam epitaxy (SMBE) on single-crystal Si substrates have been investigated by admittance spectroscopy with temperature scanning and by DLTS. The total density of electrically active centers is defined by shallow donor centers with ionization energies of 0.016–0.045 eV. The effect of growth conditions and post-growth annealing on the composition and density of electrically active centers has been studied. Significant differences in composition of the electrically active centers with deep levels and in channels of energy transfer from the electron subsystem of a crystal to Er3+ ions between Si:Er layers grown by SMBE and ion implantation have been revealed.

Optically active layers of silicon doped with erbium during sublimation molecular-beam epitaxy

A study is made of the electrical, optical, and structural properties of Si:Er layers produced by sublimation molecular-beam epitaxy. The Er and O contents in the layers, grown at 400–600°C, were as high as 5×1018 and 4×1019 cm−3, respectively. The electron concentration at 300 K was ∼10% of the total erbium concentration and the electron mobility was as high as 550 cm2/(V·s). Intense photoluminescence at 1.537 µm was observed from all the structures up to 100–140 K. The structure of the optically active centers associated with Er depended on the conditions under which the layers were grown.

Mechanism of the subband excitation of photoluminescence from erbium ions in silicon under high-intensity optical pumping

The photoluminescence (PL) excitation spectra of erbium and band-to-band silicon in Si:Er/Si epitaxial structures under high-intensity pulsed optical excitation are studied. It is shown that the nonmonotonic dependence of the PL intensity on the excitation wavelength λex near the absorption edge of silicon is due to inhomogeneity in the optical excitation of the Si:Er active layer. The sharp rise in the erbium PL intensity in the spectral range λex = 980−1030 nm is due to an increase in the excited part of the Si:Er emitting layer on passing to subband light pumping (λex > 980 nm) with a low absorption coefficient in silicon because of the effective propagation of the excitation light in the bulk of the structures under study. It is shown that, under the subband optical pumping of Si:Er/Si structures, as also in the case of interband pumping, the exciton mechanism of erbium ion excitation is operative. Excitons are generated under the specified conditions as a result of a two-stage absorption process involving impurity states in the band gap of silicon.

Determination of the excitation cross section of photoluminescence from an Er ion in the case of homogeneous and inhomogeneous optical excitation

Dependences of the erbium photoluminescence intensity in Si:Er/Si structures have been studied in cases of homogeneous (over the sample surface) and inhomogeneous optical excitation. It is shown that the excitation mode strongly affects the type of the dependences obtained. A method for determining the excitation cross section of the Er ion under both continuous and pulsed optical pumping is discussed. The value obtained for the effective excitation cross section of erbium ions in silicon, σ = 5 × 10−14 cm2 at a temperature of 8 K, is an order of magnitude larger than the values known from published material.

Specific features of the mechanisms of excitation of erbium photoluminescence in epitaxial Si:Er/Si structures

The excitation spectra and kinetics of erbium photoluminescence and silicon interband photoluminescence in Si:Er/Si structures under conditions of high-intensity pulse optical excitation are studied. It is shown that, in the interband photoluminescence spectra of the Si:Er/Si structures, both the luminescence of free excitons and the emission associated with the electron-hole plasma can be observed, depending on the excitation power and wavelength. It is found that the formation of a peak in the erbium photoluminescence excitation spectra at high pumping powers correlates with the Mott transition from the exciton gas to the electron-hole plasma. It is demonstrated that, in the Si:Er/Si structures, the characteristic rise times of erbium photoluminescence substantially depend on the concentration of charge carriers.

Electrical properties of Si:Er/Si layers grown by sublimation molecular-beam epitaxy

Temperature dependences of the concentration and electron Hall mobility in Si:Er/Sr epitaxial layers grown at T = 600°C and annealed at 700 or 900°C have been investigated. The layers were grown by sublimation molecular-beam epitaxy in vacuum (∼10−5 Pa). The energy levels of Er-related donor centers are located 0.21–0.27 eV below the bottom of the conduction band of Si. In the range 80–300 K, the electron Hall mobility in unannealed Si:Er epitaxial layers was lower than that in Czochralski-grown single crystals by a factor of 3–10. After annealing the layers, the fraction of electron scattering from Er donor centers significantly decreases.

Erbium ion electroluminescence in p ++/n +/n-Si:Er/n ++ silicon diode structures

Results of experimental studies of erbium ion electroluminescence in p++/n+/n-Si:Er/n++ silicon diode structures grown by sublimation molecular-beam epitaxy are discussed. The distinctive feature of these structures is that the regions of electron flux formation of (n+-Si) and impact excitation of erbium ions (n-Si:Er) are spaced. The influence of the n+-Si layer thickness on electrical and electroluminescent properties of diodes was studied. It was shown that n+-Si layer thinning causes the transformation of the structure breakdown mechanism from tunneling to avalanche. The dependence of the Er3+ ion electroluminescence on the thickness of the heavily doped n+-Si region is bell-shaped. At the n+-Si-layer doping level n ≈ 2 × 1018 cm−3, the maximum electroluminescence intensity is attained at an n+-Si layer thickness of ∼23 nm.