Photoluminescence properties of size-controlled silicon nanocrystals at low temperatures

International audienceThis study attempts to clarify the origin of the temperature dependence of the photoluminescence ͑PL͒ spectra of silicon nanocrystals ͑Si-ncs͒ embedded in SiO 2 from 5 to 300 K. For this purpose, size-controlled Si-ncs with a narrow size distribution were fabricated, using the SiO/ SiO 2 multilayer structure. The PL intensity is strongly temperature dependent and presents a maximum at around 70 K, depending on the Si-nc size and on the excitation power. The origin of this maximum is first discussed thanks to PL dynamics study and power dependence study. The evolution of the PL energy with temperature is also discussed. In bulk semiconductors the temperature dependence of the gap is generally well represented by Varshni's law. Taking into account the quantum confinement energy, the PL energy of Si-ncs follows very well this law in the range 50-300 K. Below 50 K, a strong discrepancy to this law is observed characterized by a strong increase in the PL energy at low temperature, which is dependent on the Si-nc size distribution. This temperature dependence of the PL energy is correlated with a decrease in the radiative rate at low temperature and is explained by a preferential saturation effect of the bigger Si-ncs

Influence of the annealing treatments on the luminescence properties of SiO∕SiO2 multilayers

International audienceThe formation of silicon nanocrystals ͑Si-ncs͒ and their room temperature photoluminescence ͑PL͒ properties were investigated in samples elaborated by the evaporation method. Silicon oxide ͑SiO͒ single layer and SiO / SiO 2 multilayers with different SiO layer thicknesses from 1 to 5 nm were prepared and annealed at different temperatures up to 1050°C. The structure and the formation of Si-nc were studied by transmission electron microscopy ͑TEM͒ and by Fourier transform infrared ͑FTIR͒ absorption spectroscopy. It is demonstrated that the Si-ncs appear by the phase separation process from SiO due to the annealing treatments. Contrary to the SiO single layer, the multilayers are a powerful system to obtain highly luminescent Si-nc and to control the Si-nc size for SiO layer thicknesses lower than or equal to 4 nm. It is clearly shown that, in agreement with the quantum confinement theory, the PL energy is a decreasing function of the Si-nc size. However, thanks to the correlation between FTIR, TEM, and PL results, it is demonstrated that the PL energy is also strongly dependent on the quality of the matrix in which the Si-nc are embedded. A model based on the existence of a SiO x shell surrounding the Si-nc is proposed to explain the PL results

Luminescence efficiency at 1.5 μm of Er-doped thick SiO layers and Er-doped SiO∕SiO2 multilayers

International audienceThe luminescence from Er-doped thin films is studied in two different systems. The first one is a SiO single layer. The second one is a SiO / SiO 2 multilayer allowing us to obtain size-controlled silicon nanocrystals. In both systems, the annealing-temperature dependence of the luminescence is investigated. It is shown that the optimal annealing temperatures are equal to 700 and 1050°C for the single layer and the multilayer, respectively. Moreover the luminescence efficiency at 1.5 m is one order of magnitude higher in the single Er-doped SiO layer. These results are discussed in relation to the formation of silicon nanoparticles with annealing treatments

Resistive switching in silicon suboxide films

We report a study of resistive switching in a silicon-based memristor/resistive RAM (RRAM) device in which the active layer is silicon-rich silica. The resistive switching phenomenon is an intrinsic property of the silicon-rich oxide layer and does not depend on the diffusion of metallic ions to form conductive paths. In contrast to other work in the literature, switching occurs in ambient conditions, and is not limited to the surface of the active material. We propose a switching mechanism driven by competing field-driven formation and current-driven destruction of filamentary conductive pathways. We demonstrate that conduction is dominated by trap assisted tunneling through noncontinuous conduction paths consisting of silicon nanoinclusions in a highly nonstoichiometric suboxide phase. We hypothesize that such nanoinclusions nucleate preferentially at internal grain boundaries in nanostructured films. Switching exhibits the pinched hysteresis I/V loop characteristic of memristive systems, and on/off resistance ratios of 104:1 or higher can be easily achieved. Scanning tunneling microscopy suggests that switchable conductive pathways are 10 nm in diameter or smaller. Programming currents can be as low as 2 μA, and transition times are on the nanosecond scale

Erbium implanted silicon rich oxide thin films suitable for slot waveguides applications

n/

Electrical behavior of MIS devices based on Si nanoclusters embedded in SiOxNy and SiO2 films

We examined and compared the electrical properties of silica (SiO2) and silicon oxynitride (SiOxNy) layers embedding silicon nanoclusters (Sinc) integrated in metal-insulator-semiconductor (MIS) devices. The technique used for the deposition of such layers is the reactive magnetron sputtering of a pure SiO2 target under a mixture of hydrogen/argon plasma in which nitrogen is incorporated in the case of SiOxNy layer. Al/SiOxNy-Sinc/p-Si and Al/SiO2-Sinc/p-Si devices were fabricated and electrically characterized. Results showed a high rectification ratio (>104) for the SiOxNy-based device and a resistive behavior when nitrogen was not incorporating (SiO2-based device). For rectifier devices, the ideality factor depends on the SiOxNy layer thickness. The conduction mechanisms of both MIS diode structures were studied by analyzing thermal and bias dependences of the carriers transport in relation with the nitrogen content

Expression analysis of Clavata1-like and Nodulin21-like genes from Pinus sylvestris during ectomycorrhiza formation

The ecology and physiology of ectomycorrhizal (EcM) symbiosis with conifer trees are well documented. In comparison, however, very little is known about the molecular regulation of these associations. In an earlier study, we identified three EcM-regulated Pinus expressed sequence tags (EST), two of which were identified as homologous to the Medicago truncatula nodulin MtN21. The third EST was a homologue to the receptor-like kinase Clavata1. We have characterized the expression patterns of these genes and of auxin- and mycorrhiza-regulated genes after induction with indole-3-butyric acid in Pinus sylvestris and in a time course experiment during ectomycorrhizal initiation with the co-inoculation of 2,3,5-triiodobenzoic acid, an auxin transport inhibitor. Our results suggest that different P. sylvestris nodulin homologues are associated with diverse processes in the root. The results also suggest a potential role of the Clv1-like gene in lateral root initiation by the ectomycorrhizal fungus

Current transport and electroluminescence mechanisms in thin SiO2 films containing Si nanocluster-sensitized erbium ions.

We have studied the current transport and electroluminescence properties of metal oxide semiconductor MOS devices in which the oxide layer, which is codoped with silicon nanoclusters and erbium ions, is made by magnetron sputtering. Electrical measurements have allowed us to identify a Poole-Frenkel conduction mechanism. We observe an important contribution of the Si nanoclusters to the conduction in silicon oxide films, and no evidence of Fowler-Nordheim tunneling. The results suggest that the electroluminescence of the erbium ions in these layers is generated by energy transfer from the Si nanoparticles. Finally, we report an electroluminescence power efficiency above 10−3%. © 2009 American Institute of Physics. doi:10.1063/1.321338