Low-temperature growth of silicon epitaxial layers codoped with erbium and oxygen atoms

The fabrication technology and properties of light-emitting Si structures codoped with erbium and oxygen are reported. The layers are deposited onto (100) Si by molecular beam epitaxy (MBE) using an Er-doped silicon sublimation source. The partial pressure of the oxygen-containing gases in the growth chamber of the MBE facility before layer growth is lower than 5 × 10^?10 Torr. The oxygen and erbium concentrations in the Si layers grown at 450°C is ～1 × 10¹⁹ and 10¹⁸ cm^?3, respectively. The silicon epitaxial layers codoped with erbium and oxygen have high crystal quality and yield effective photoluminescence and electroluminescence signals with the dominant optically active Er-1 center forming upon postgrowth annealing at a temperature of 800°C.     

Simultaneous doping of silicon layers with erbium and oxygen in the course of molecular-beam epitaxy

Epitaxial silicon layers codoped with erbium and oxygen were grown by molecular-beam epitaxy using a silicon sublimation source. For growing the erbium-doped silicon layers, two types of impurity sources were used: (i) erbium-doped silicon plates were used as a source of fluxes of Er and Si atoms; and (ii) metallic erbium plates were used as an impurity-vapor source in combination with the silicon sublimation source. If gaseous oxygen was used for in situ codoping with erbium and oxygen, then concentrations ranging from 10¹⁸ to 10²⁰ cm^?3 were attained. When oxygen is in the growth chamber, the erbium-entrapment efficiency of a layer increases substantially, with the surface segregation of erbium also being suppressed by oxidation.     

The influence of oxygen on the formation of donor centers in silicon layers implanted with erbium and oxygen ions

A model of the formation of donor centers introduced by a combined implantation of Er⁺ and O⁺ ions into silicon with subsequent thermal annealing is developed. These centers are multiparticle erbium-oxygen complexes ErO_n with n≥4. The competing process of formation of electrically inactive oxygen clusters is taken into account. The model makes it possible to describe the dependence of the activation coefficient for the donor centers on the implantation dose of oxygen ions and, also, the effects of the oxygen ion implantation and annealing temperature on the concentration profiles of the donor centers.     

A model for the formation of donor centers in silicon layers implanted with erbium and oxygen ions

Formation of donor centers in the course of annealing of layers of single-crystal silicon FZ-Si (grown by the float-zone method) and Cz-Si (grown by the Czochralski method) implanted with Er⁺ and O⁺ ions was simulated. The diffusion-kinetics equations accounting for the formation of erbium-related donor centers of three types were solved numerically. These centers were formed with the involvement of oxygen in the substrate or implanted oxygen and also self-interstitials I produced during annealing of implantation-induced defects; i.e., the Er-I, Er-O, and Er-O-I centers were considered. The results of calculations satisfactorily describe the concentration profiles of donor centers and also the influence of oxygen in the substrate and implanted oxygen on the dependence of the donor-activation coefficient of erbium on the annealing temperature in the range of 600–1200°C.     

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 ??_ex 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 ??_ex = 980?1030 nm is due to an increase in the excited part of the Si:Er emitting layer on passing to subband light pumping (??_ex > 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.     

Photoluminescence of erbium ions in heterostructures with silicon nanocrystals

Photoluminescence properties of erbium-doped silicon dioxide layers containing silicon nanocrystals with 1.5–4.5 nm average size are investigated. It is found that the intensity and mean lifetime of the Er³⁺-ion photoluminescence depend on the nanocrystal size, optical pump intensity, and temperature. The results obtained are explained both by the effect of the local environment on Er³⁺ ions and by the manifestation of nonradiative deexcitation of ions caused by the transfer of energy back into the solid-state matrix and the Auger processes.     

Theoretical analysis of the dynamic behavior of highly-efficient erbium/ytterbium codoped fiber lasers

A numerical study of the transient behavior of single-mode Er/sup 3+//Yb/sup 3+/ codoped fiber lasers is presented. The model, based on propagation-rate equations, includes both uniform up-conversion from the /sup 4/I/sub 15/2/ and /sup 4/I/sub 9/2/ erbium levels and the pair-induced energy transfer process from ytterbium to erbium. We show that neglecting the r dependence of the operating fiber laser parameters allows accurate simulation results at minimum numerical effort. Using this numerical model, we characterize the laser relaxation oscillations and the effect of ytterbium on the dynamic behavior and stability with respect to fluctuations of the pump power. Our results confirm that the presence of Yb/sup 3+/ enhances the efficiency of the laser and show that its stability is also significantly improved.     

Seeded erbium/ytterbium codoped fibre amplifier source with 87 W of single-frequency output power

A highly efficient cladding-pumped erbium/ytterbium-doped large-core fibre amplifier, generating up to 87 W of single-frequency continuous-wave output at 1563 nm, with a good beam quality (M/sup 2//spl les/1.7), in a master oscillator power amplifier configuration is reported. The overall optical power conversion efficiency was 26%.     

Photoluminescence of erbium in amorphous hydrogenated phosphorus-doped silicon

The photoluminescence of erbium ions in phosphorus-doped a-Si:H films has been investigated. The observed increase in the Er photoluminescence with increasing defect density in the samples and the correlation of the temperature variation of the Er photoluminescence and defect-associated photoluminescence intensities are explained on the basis of a model of excitation of Er ions as a result of Auger recombination with defect participation. Fiz. Tekh. Poluprovodn. 31, 869–871 (July 1997)     

Mechanism of erbium electroluminescence in hydrogenated amorph silicon

The mechanism of the electroluminescence of erbium under a reverse bias in structures based on hydrogenated amorphous silicon is studied. Erbium ions are excited through an Auger process, in which conduction electrons are trapped by neutral dangling bonds (D ⁰ centers) located near the erbium ions. A stationary current through the structure is sustained by a reverse process involving the thermally stimulated tunneling emission of electrons by negatively charged dangling-bond defects (D ⁰ centers) into the conduction band of the amorphous matrix. Fiz. Tekh. Poluprovodn. 33, 671–673 (June 1999)     

Electrical properties of silicon layers implanted with erbium and oxygen ions in a wide dose range and thermally treated in different temperature conditions

The electrical properties of silicon implanted with Er and O ions in a wide dose range have been studied. The dependence of electron mobility on the concentration of electrically active centers is determined for Si:Er layers with Er concentrations in the range of 9×10¹⁵–8×10¹⁶ cm^?3. Sharp bends related to specific features of Er segregation in solid-phase epitaxial recrystallization are observed in the concentration profiles of electrically active centers, n(x), and Er atoms, C(x), at Er ion implantation doses exceeding the amorphization threshold. The n(x) and C(x) profiles virtually coincide near the surface. A linear rise in the maximum concentration of electrically active centers at approximately constant effective coefficient of their activation, k, is observed at Er implantation doses exceeding the amorphization threshold. At an Er concentration higher than 7×10¹⁹ cm^?3, the concentration of electrically active centers levels off and k decreases.     

Photoluminescence in silicon implanted with erbium ions at an elevated temperature

Photoluminescence spectra of n-type silicon upon implantation with erbium ions at 600°C and oxygen ions at room temperature and subsequent annealings at 1100°C in a chlorine-containing atmosphere have been studied. Depending on the annealing duration, photoluminescence spectra at 80 K are dominated by lines of the Er³⁺ ion or dislocation-related luminescence. The short-wavelength shift of the dislocation-related luminescence line observed at this temperature is due to implantation of erbium ions at an elevated temperature. At room temperature, lines of erbium and dislocation-related luminescence are observed in the spectra, but lines of near-band-edge luminescence predominate.     

Oxygen and Erbium related donor centers in Czochralski grown silicon implanted with erbium

The Hall effect measurements were conducted on Czochralski-grown silicon after implantation of erbium and two-step annealing at 700 °C and 900 °C. After the first step the formation of oxygen-related shallow donors was observed at E _c in the range 20–40 meV and erbium-related donor centers at ≈E _c -70 meV and ≈E _c -120 meV. Along with the same oxygen-related shallow thermal donors and donor centers at ≈E _c -70 meV, other donor centers at ≈E _c -150 meV are formed following the 900°C anneal, instead of those at ≈E _c -120 meV. The new donor states are of particular interest because of their possible involvement in the photoluminescence process. The obtained results for erbium-implanted silicon are compared with some fragmentary DLTS data found in the current literature on the donors with ionization energies less than 0.2 eV. Fiz. Tekh. Poluprovodn. 33, 1192–1195 (October 1999)     

The density of states in the mobility gap of amorphous hydrogenated silicon doped with erbium

The effect of doping films of amorphous hydrogenated silicon (a-Si:H) with erbium on the density of the states in the mobility gap is studied. The data obtained are compared with those for a-Si:H films doped with arsenic. The data on the density of the states in the lower and upper halves of the mobility gap are determined from measurements of the spectral dependences of the absorption coefficient and the temperature dependences of the constant and modulated components of the photoconductivity in films exposed to modulated light, respectively. It is shown that doping the a-Si:H films with erbium leads to an increase in the density of states both in the lower and upper halves of the mobility gap.     

Luminescence of erbium in amorphous hydrogenated silicon obtained by the glow-discharge method

We report the first observation of efficient room-temperature photoluminescence of erbium in amorphous hydrogenated silicon prepared by the plasma chemical-deposition method. Fiz. Tekh. Poluprovodn. 32, 987–989 (August 1998)     

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. Fiz. Tekh. Poluprovodn. 33, 156–160 (February 1999)     

Redistribution of erbium during the crystallization of buried amorphous silicon layers

The redistribution of Er during its implantation in silicon at doses close to the amorphization threshold and its subsequent solid-phase epitaxial (SPE) crystallization is investigated. The formation of a buried amorphous (a) layer is discovered at Er doses equal to 5×10¹³ and 1×10¹⁴ cm⁻² using Rutherford backscattering. The segregation of Er in this case takes place inwardly from the two directions corresponding to the upper and lower boundaries of the buried αlayer and leads to the formation of a concentration peak at the meeting place of the two crystallization fronts. A method for calculating the coordinate dependence of the segregation coefficient k from the distribution profiles of the erbium impurity before and after annealing is proposed. The k(x) curve exhibits a drop, whose width increases with decreasing Er implantation dose. Its appearance is attributed to the nonequilibrium nature of the segregation process at the beginning of SPE crystallization. Fiz. Tekh. Poluprovodn. 33, 652–655 (June 1999)     

White-light emission from InGaN-GaN multiquantum-welllight-emitting diodes with Si and Zn codoped active well layer

Si and Zn codoped In_xGa_1-xN-GaN multiple-quantum-well (MQW) light-emitting diode (LED) structures were grown by metal-organic vapor phase epitaxy (MOVPE). It was found that we can observe a broad long-wavelength donor-acceptor (D-A) pair related emission at 500 nm~560 nm. White light can thus be achieved by the combination of such a long-wavelength D-A pair emission with the InGaN bandedge related blue emission. It was also found that the electroluminescence (EL) spectra of such Si and Zn codoped InGaN-GaN MQW LEDs are very similar to those measured from phosphor-converted white LEDs. That is, we can achieve white light emission without the use of phosphor by properly adjusting the indium composition and the concentrations of the codoped Si and Zn atoms in the active well layers and the amount of injection current     

Specific features of erbium ion photoluminescence in structures with amorphous and crystalline silicon nanoclusters in silica matrix

Photoluminescence properties of the structures of amorphous and crystalline silicon nanoclusters with average sizes no larger than 4 nm in an erbium-doped silicon dioxide matrix were studied. It was found that the photoluminescence lifetime of Er³⁺ ions at a wavelength of 1.5 μm decreases from 5.7 to 2.0 ms and from 3.5 to 1.5 ms in samples with amorphous nanoclusters and with nanocrystals, respectively, as the Er³⁺ concentration increases from 10¹⁹ to 10²¹ cm^?3. The decrease in the erbium photoluminescence lifetime with the ion concentration is attributed to the effects of concentration-related quenching and residual implantation-induced defects. The difference between lifetimes for samples with amorphous and crystalline nanoclusters is interpreted as the effect of different probabilities of energy back transfer from Er³⁺ ions to the solid-state matrix in the structures under consideration.