D. I. Kryzhkov

Lanthanide complexes with substituted naphtholate ligands: extraordinary bright near-infrared luminescence of ytterbium

A series of Pr, Nd, Ho, Er, Tm, and Yb complexes with 3-(2-benzoxazol-2-yl)-2-naphtholate and 3-(2-benzothiazol-2-yl)-2-naphtholate ligands was synthesized. The structure, as well as the photo- and electroluminescent properties of these complexes were studied. An extraordinary bright emission of Yb3+ was detected. To explain the phenomenon, a novel excitation mechanism involving intramolecular electron transfer was proposed.

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.

Smbe Grown Uniformly And Selectively Doped Si:Er Structures For Leds And Lasers

In recent years an increasing attention has been focused on the investigation of optically active Er centers in Si in view of great application possibilities opened for this material. The intra-center emission of Er3+ ions occurs at a wavelength of 1.54 urn where silica based optical fibers are known to have minimum loss and low dispersion. It makes Si:Er attractive as a light emitting source for fiber optics communication systems. Moreover, the realization of efficient light emitters on Si will offer new opportunities in the application of Si-based optoelectronic devices for large-scale integrated circuits. The methods commonly used for incorporating Er into silicon are ion implantation [1] and molecular beam epitaxy (MBE) [4]. In this contribution we present an original method of sublimation MBE (SMBE) [7] and describe its capabilities for growth of effective light-emitting Si:Er-based structures including light-emitting diodes operating at room temperature. Along with the SMBE grown uniform Si:Er layers, the photoluminescence (PL) efficiency of which is comparable with or even higher than that of the ion- implanted layers, we consider here a novel type of Er-doped structures — the selectively doped Si/Si:Er/Si/Si:Er…/Si multilayer structures with enhanced photo- and electroluminescence (EL) efficiency [9]. Finally, we provide the results of simulations for the parameters of real laser-type structures and discuss the prospects of achieving stimulated emission on their basis.

Type II–type I conversion of GaAs/GaAsSb heterostructure energy spectrum under optical pumping

We present the experimental results of time-resolved photoluminescence spectroscopy in type II GaAs/GaAs0.64Sb0.36 quantum well heterostructures. At moderate optical excitation densities (below 103 W/cm2), we observe blue shift of the photoluminescence peak with increasing pump power which results from band bending at the type II heterointerface due to photo-excited charge carriers. With further increase in the excitation density, the observed peak undergoes red shift accompanied by significant drop in the luminescence decay time (from 10 ns to 1 ns) which is caused by extreme band bending and increasing contribution of type I radiative transitions to the photoluminescence signal.

Er-Doped Electro-Optical Memory Element for 1.5-

Silicon photonics is rapidly growing and a number of Si-based active and passive components have recently been demonstrated. We demonstrate new functionality of Er-doped silicon: a memory effect in electroluminescence. This finding opens a prospect of necessary, and thus far not available, component for Si optoelectronics-a fully complimentary metal-oxide-semiconductor-compatible electro-optical converter with a memory function, operating in the technologically important 1.5-mum band. When developed and optimized, prospect applications could include optical intraand inter-chip connectors and volatile flash memory elements

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The results of experimental studies of the subpicosecond relaxation dynamics of photoexcited charge carriers in an In0.22Ga0.78As/GaAs quantum-well heterostructure are reported. From photoluminescence studies of the structure by the upconversion technique, the cooling rate of charge carriers in the quantum well and the time of charge-carrier trapping into the well are estimated to be ∼1 ps at 300 K and at ∼6.5 ps at 10 K.

m Silicon Photonics

The type of heterojunction in the GaAs1 − xSbx/GaAs heterostructure at x = 0.36 is studied by photoluminescence spectroscopy and time-resolved photoluminescence. A GaAsSb/GaAs heterostructure with an Sb fraction of 15%, for which we can confidently state is a type-I heterojunction, was studied for comparison. It was established from the blue shift of the photoluminescence line depending on the excitation power and relaxation time of the photoluminescence signal from the GaAs1 − xSbx/GaAs quantum well, which was ∼11 ns, that the GaAs1 − xSbx/GaAs structure at an Sb content of 36% clearly constitutes a type II heterojunction. This was additionally evidenced by the data obtained for structures with an Sb content of 15%, in which case no shift of the location of the photoluminescence line on the pump power was observed, while the relaxation time of photoluminescence in the region of the signal from the quantum well was ∼1.5 ns.

Picosecond photoluminescence dynamics in an InGaAs/GaAs quantum-well heterostructure

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 heterojunction type in structures with GaAsSb/GaAs quantum wells with various antimony fractions by optical methods

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.

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

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.