Defect-engineered blue-violet electroluminescence from Ge nanocrystal rich SiO2 layers by Er doping
TL;DR: Using combined microstructural and electroluminescence (EL) investigations of the Er-doped Ge-rich SiO2 layers, it was established that the Ge-related oxygen-deficiency centers (GeODCs), which are associated with the 407 nm light emission, are situated at the Ge nanocrystal/SiO2 interface as mentioned in this paper.
Abstract: Using combined microstructural and electroluminescence (EL) investigations of the Er-doped Ge-rich SiO2 layers, it is established that the Ge-related oxygen-deficiency centers (GeODCs), which are associated with the 407 nm light emission, are situated at the Ge nanocrystal/SiO2 interface. Electrically driven energy transfer from the Er3+ to GeODCs causes an increase in the 407 nm EL intensity. It reaches a maximum before quenching with increasing Er concentration due to the crystalline-to-amorphous transition of Ge nanocrystals. Ge concentration dependent quenching of the maximum EL intensity and the peak shifting toward higher Er concentration are discussed in terms of the reduction of the surface-to-volume ratio with increasing nanocrystal size.
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TL;DR: In this paper, the size-dependent electrical and optical properties of group-IV semiconductors (Si and Ge), metal and high-k NCs for silicon planar technology compatible light-emitting and floating gate memory devices are discussed.
Abstract: Nanocrystals (NCs), representing a zero-dimensional system, are an ideal platform for exploring quantum phenomena on the nanoscale, and are expected to play a major role in future electronic and photonic devices. Here we review recent progress in the growth, characterization and utilization of some group-IV semiconductors (Si and Ge), metal and high-k NCs for silicon planar technology compatible light-emitting and floating gate memory devices. We first introduce the size-dependent electrical and optical properties of Si and Ge NCs. We outline some of the schemes to achieve light emission from indirect band gap Si and Ge NCs embedded in different high band gap oxide matrices. In particular, special emphasis is given on the review of the advances in Ge NCs because of some of their intriguing electronic and optical properties. We then describe the use of semiconductor and metal NCs as floating gates for non-volatile memory devices to achieve high data retention and faster program/erase speeds. The exploitation of high-k oxides with tunable and variable injection barriers for improved charge storage devices is discussed. Finally, the integration of single and multilayer metallic NCs and multilayer high-k oxides as floating gates is explored by the fabrication and testing of memory transistors.
106 citations
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TL;DR: The evolution of the nanoscale structure upon an annealing treatment was found to control the interrelation between the radiative recombination of the carriers via Si clusters and via 4f shell transitions in Er3+ ions.
Abstract: Photoluminescence spectroscopy and atom probe tomography were used to explore the optical activity and microstructure of Er3+-doped Si-rich SiO2 thin films fabricated by radio-frequency magnetron sputtering. The effect of post-fabrication annealing treatment on the properties of the films was investigated. The evolution of the nanoscale structure upon an annealing treatment was found to control the interrelation between the radiative recombination of the carriers via Si clusters and via 4f shell transitions in Er3+ ions. The most efficient 1.53-μ m Er3+ photoluminescence was observed from the films submitted to low-temperature treatment ranging from 600°C to 900°C. An annealing treatment at 1,100°C, used often to form Si nanocrystallites, favors an intense emission in visible spectral range with the maximum peak at about 740 nm. Along with this, a drastic decrease of 1.53-μ m Er3+ photoluminescence emission was detected. The atom probe results demonstrated that the clustering of Er3+ ions upon such high-temperature annealing treatment was the main reason. The diffusion parameters of Si and Er3+ ions as well as a chemical composition of different clusters were also obtained. The films annealed at 1,100°C contain pure spherical Si nanocrystallites, ErSi3O6 clusters, and free Er3+ ions embedded in SiO2 host. The mean size and the density of Si nanocrystallites were found to be 1.3± 0.3 nm and (3.1± 0.2)×1018 Si nanocrystallites·cm−3, respectively. The density of ErSi3O6 clusters was estimated to be (2.0± 0.2)×1018 clusters·cm−3, keeping about 30% of the total Er3+ amount. These Er-rich clusters had a mean radius of about 1.5 nm and demonstrated preferable formation in the vicinity of Si nanocrystallites.
31 citations
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TL;DR: It is demonstrated that Ge nanocrystals act as strong sensitizers for Er(3+) ions emission and the effective Er excitation cross section increases by almost four orders of magnitude with respect to the one without Ge nanocystals.
Abstract: Photo-physical processes in Er-doped silica glass matrix containing Ge nanocrystals prepared by the sol–gel method are presented in this article Strong photoluminescence at 154 μm, important for fiber optics telecommunication systems, is observed from the different sol–gel derived glasses at room temperature We demonstrate that Ge nanocrystals act as strong sensitizers for Er 3+ ions emission and the effective Er excitation cross section increases by almost four orders of magnitude with respect to the one without Ge nanocrystals Rate equations are considered to demonstrate the sensitization of erbium luminescence by Ge nanocrystals Analyzing the erbium effective excitation cross section, extracted from the flux dependent rise and decay times, a Dexter type of short range energy transfer from a Ge nanocrystal to erbium ion is established
14 citations
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TL;DR: The time resolved characteristics of the Er induced emission peak have been studied as a function of the pump flux as well as the diameter of the Ge nanowires.
Abstract: We have fabricated Er doped germanium nanowires of different diameters by pulsed laser deposition and chemical methods. Er induced photoluminescence emission due to the intra-4f 4I13/2→4I15/2 transition of Er energy levels at 1.53 µm has been achieved at room temperature using both resonant (980 nm) and non-resonant (325 nm) excitation of Er ions. The observed 1.53 µm photoluminescence signal upon non-resonant 325 nm excitation is attributed to the Ge related oxygen deficiency centers surrounding the Ge core. For direct excitation, the infrared photoluminescence characteristics have been studied as a function of Er concentration, photon flux, and diameter of the nanowires. The Er related emission signal is found to be enhanced with increase in Er concentration, pump flux of 980 nm, and the nanowire diameter. The time resolved characteristics of the Er induced emission peak have been studied as a function of the pump flux as well as the diameter of the Ge nanowires.
13 citations
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TL;DR: In this article, the size dependent photoresponse behavior of crystalline Ge quantum dots (QDs) dispersed within the silica matrix was investigated and the effect of Coulomb interaction of photogenerated carriers, QD/silica interface defects and electric field driven carrier separation and tunneling through the oxide barriers.
Abstract: We report on the size dependent photoresponse behaviour of crystalline Ge quantum dots (QDs) dispersed within the silica matrix. Our findings demonstrate an increasing nature of EQE with increase in QDs size, which could be attributed to the combined effect of Coulomb interaction of photogenerated carriers, QD/silica interface defects and electric field driven carrier separation and tunneling through the oxide barriers. In this regard, the bias dependent nonlinear response of the photocurrent has been explained on the basis of cold field emission (CFE) model. Besides, the EQE is extended (>100%) for larger sized QDs, suggesting the trapping of slower holes in Ge QDs creating a charge neutrality issue.
8 citations
References
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TL;DR: In this paper, SiO2 films containing Si nanocrystals (nc-Si) and Er were studied and their photoluminescence properties were assigned to electron-hole recombination in nc-Si and the intra-4f transition in Er3+, respectively.
Abstract: SiO2 films containing Si nanocrystals (nc-Si) and Er were prepared and their photoluminescence (PL) properties were studied. The samples exhibited luminescence peaks at 0.81 and 1.54 μm, which could be assigned to the electron-hole recombination in nc-Si and the intra-4f transition in Er3+, respectively. Correlation between the intensities of the two luminescence peaks was studied as functions of Er concentration and excitation power. The present results clearly demonstrate that excitation of Er3+ occurs through the recombination of photogenerated carriers spatially confined in nc-Si and the subsequent energy transfer to Er3+.
557 citations
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TL;DR: In this paper, the melting behavior of Ge nanocrystals embedded within SiO sub 2 was evaluated using in situ transmission electron microscopy, and the observed melting point hysteresis is large ({+-} 17%) and nearly symmetric about the bulk melting point.
Abstract: The melting behavior of Ge nanocrystals embedded within SiO{sub 2} is evaluated using in situ transmission electron microscopy. The observed melting point hysteresis is large ({+-} 17%) and nearly symmetric about the bulk melting point. This hysteresis is modeled successfully using classical nucleation theory without the need to invoke epitaxy.
111 citations
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04 May 2006
TL;DR: The melting behavior of Ge nanocrystals embedded within SiO2 is evaluated using in situ transmission electron microscopy and the observed melting-point hysteresis is large and nearly symmetric about the bulk melting point.
Abstract: Large melting point hysteresis of Ge nanocrystals embedded in SiO 2 Q. Xu, 1, 2 I. D. Sharp, 1, 2 C. W. Yuan, 1, 2 D. O. Yi, 3, 2 C. Y. Liao, 1, 2 A. M. Glaeser, 1, 2 A. M. Minor, 4 J. W. Beeman, 2 M. C. Ridgway, 5 P. Kluth, 5 J. W. Ager III, 2 D. C. Chrzan, 1, 2 and E. E. Haller 1, 2 Department of Materials Science & Engineering, University of California, Berkeley, CA 94720, USA Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Applied Science & Technology, University of California, Berkeley, CA 94720, USA National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA 94720,USA Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200, Australia (Dated: May 4, 2006) Abstract The melting behavior of Ge nanocrystals embedded within SiO 2 is evaluated using in situ transmission electron microscopy. The observed melting point hysteresis is large (±17%) and nearly symmetric about the bulk melting point. This hysteresis is modeled successfully using classical nucleation theory without the need to invoke epitaxy. PACS numbers: 64.60.-i,64.70.Dv,61.46.Hk
105 citations
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TL;DR: In this article, the interaction between Si nanoclusters Si-nc and Er in SiO2 was investigated, and the optical characterization and modeling of this system, and its effectiveness as a gain material for optical waveguide amplifiers at 1.54 m.
Abstract: This paper investigates the interaction between Si nanoclusters Si-nc and Er in SiO2, reports on the optical characterization and modeling of this system, and attempts to clarify its effectiveness as a gain material for optical waveguide amplifiers at 1.54 m. Silicon-rich silicon oxide layers with an Er content of 4 – 6 10 20 at./ cm 3 were deposited by reactive magnetron sputtering. The films with Si excess of 6 – 7 at. %, and postannealed at 900 ° C showed the best Er 3+ photoluminescence PL intensity and lifetime, and were used for the study. The annealing duration was varied up to 60 min to engineer the size and density of Si-nc and optimize Si-nc and Er coupling. PL investigations under resonant 488 nm and nonresonant 476 nm pumping show that an Er effective excitation cross section is similar to that of Si-nc 10 �17 –1 0 �16 cm 2 at low pumping flux 10 16 –1 0 17 cm �2 s �1 , while it drops at high flux 10 18 cm �2 s �1 . We found a maximum fraction of excited Er of about 2% of the total Er content. This is far from the 50% needed for optical transparency and achievement of population inversion and gain. Detrimental phenomena that cause depletion of Er inversion, such as cooperative up conversion, excited-stated absorption, and Auger deexcitations are modeled, and their impact in lowering the amount of excitable Er is found to be relatively small. Instead, Auger-type short-range energy transfer from Si-nc to Er is found, with a characteristic interaction length of 0.4 nm. Based on such results, numerical and analytical Er as a quasi-two-level system coupled rate equations have been developed to determine the optimum conditions for Er inversion. The modeling predicts that interaction is quenched for high photon flux and that only a small fraction of Er 0.2–2 % is excitable through Si-nc. Hence, the low density of sensitizers Si-nc and the short range of the interaction are the explanation of the low fraction of Er coupled. Efficient ways to improve Er-doped Si-nc thin films for the realization of practical optical amplifiers are also discussed.
91 citations