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Effect of annealing treatments on photoluminescence and charge storage mechanism in silicon-rich SiNx:H films.

Sahu BS, Delachat F, Slaoui A, Carrada M, Ferblantier G, Muller D - Nanoscale Res Lett (2011)

Bottom Line: The silicon-rich a-SiNx:H films (SRSN) were sandwiched between a bottom thermal SiO2 and a top Si3N4 layer, and subsequently annealed within the temperature range of 500-1100°C in N2 to study the effect of annealing temperature on light-emitting and charge storage properties.A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C.A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices.

View Article: PubMed Central - HTML - PubMed

Affiliation: InESS-UdS-CNRS, 23 Rue du Loess, 67037 Strasbourg, France. sahu.bhabani@iness.c-strasbourg.fr.

ABSTRACT
In this study, a wide range of a-SiNx:H films with an excess of silicon (20 to 50%) were prepared with an electron-cyclotron resonance plasma-enhanced chemical vapor deposition system under the flows of NH3 and SiH4. The silicon-rich a-SiNx:H films (SRSN) were sandwiched between a bottom thermal SiO2 and a top Si3N4 layer, and subsequently annealed within the temperature range of 500-1100°C in N2 to study the effect of annealing temperature on light-emitting and charge storage properties. A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C. The possible origins of the PL are briefly discussed. The authors have succeeded in the formation of amorphous Si quantum dots with an average size of about 3 to 3.6 nm by varying excess amount of Si and annealing temperature. Electrical properties have been investigated on Al/Si3N4/SRSN/SiO2/Si structures by capacitance-voltage and conductance-voltage analysis techniques. A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices.

No MeSH data available.


Roomtemperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films. (a) (Color online) Room temperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films having an excess of silicon from 22 to 33 at.% (samples S1, S2, S3, and S4) in the middle SRSN layer, (b) PL energies and intensities of the as-deposited films as a function of silicon excess in the SRSN layer
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Figure 4: Roomtemperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films. (a) (Color online) Room temperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films having an excess of silicon from 22 to 33 at.% (samples S1, S2, S3, and S4) in the middle SRSN layer, (b) PL energies and intensities of the as-deposited films as a function of silicon excess in the SRSN layer

Mentions: Figure 4a shows the PL spectra of the as-deposited samples. All the samples exhibit broad and strong visible PL at room temperature. The mechanism for strong luminescence from SiNx materials is commonly suggested from the combination of Si/SiNx interface luminescence, gap state luminescence/band-tail luminescence, and luminescence from Si nanodots/clusters. In this investigation, efforts have been made to minimize Si/SiNx interface luminescence with the introduction of high-quality thermal SiO2 before SiNx deposition, which gives rise to enhanced interface quality with minimal interfacial defect states. Details regarding interface traps will be discussed in the C-V analysis part. As evident from Figure 4a,b, with increase in nitrogen content in the SRSN films, the PL peak shifts to higher energies together with an increase in the relative intensity and width. This behavior is commonly attributed to a model based on quantum confinement effect (QCE) [27-29]. From the QCE model point of view, PL blue shift is caused by the reduction in Si-np size, and the increase in emission efficiency can be correlated with the onset of pseudo-direct bandgap behavior. However, no sin-np/cluster has been detected in our EFTEM analysis for these as-deposited SRN films. Thus, the role of QCE can be ruled out. The behavior of PL is in very good agreement with the findings by other authors for a-SiNx:H [30-32] and a-SiCx:H [33,34], where it has been attributed to a model based on band-tail states. In this model, the carriers radiatively recombine with the localized states at the band tails of the gap. With increasing nitrogen content, the bandgap energy increases, which results in a blue shift of the PL energy. However, for band-tail mechanism, the emission generally occurs at energies lower than 1.82 eV [11]. In this study, the peak position of PL spectra is higher than this value, especially for the samples with lower excess of Si. Furthermore, based on Robertson's calculated results [35,36], Ko et al. [37] have proposed possible mechanisms related to defect states to explain PL in silicon nitride films. Being amorphous, the samples have varying optical band gaps depending on composition. Therefore, the energy levels are not well defined. In addition, there is a distribution of states for a given defect giving rise to broad features in the PL spectra. Some investigations have shown both theoretically and experimentally that the PL band with peak positions of 1.8-3.2 eV [38-40] is closely related to the defect states within the bandgap of amorphous SiNx materials. Indeed, large amount of defect-related gap states generally exists in non-stoichiometric silicon nitride layers obtained by CVD process. These defect states having different energy levels contribute to the radiative emission by creating different channels for the relaxation of electronic states. It can be noticed that a weak peak appears around 3.1 eV, whose relative intensity decreases with increasing nitrogen content in the films. Wang et al. have attributed this peak to the presence of nitrogen-dangling bonds [41], whereas others have attributed it to the presence of ≡ Si0 defect sites, which give gap states at 3.1 eV, 80% localized on sites [36]. In this case, as the band becomes prominent at higher Si content, it can be safely assigned to ≡Si0 defect sites rather to than nitrogen-dangling bonds. From the above discussions, it can be ascertained that the predominant mechanism responsible for the PL behavior can be due to the recombination of defect states.


Effect of annealing treatments on photoluminescence and charge storage mechanism in silicon-rich SiNx:H films.

Sahu BS, Delachat F, Slaoui A, Carrada M, Ferblantier G, Muller D - Nanoscale Res Lett (2011)

Roomtemperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films. (a) (Color online) Room temperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films having an excess of silicon from 22 to 33 at.% (samples S1, S2, S3, and S4) in the middle SRSN layer, (b) PL energies and intensities of the as-deposited films as a function of silicon excess in the SRSN layer
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211231&req=5

Figure 4: Roomtemperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films. (a) (Color online) Room temperature PL spectra of as-deposited Si3N4/SRSN/SiO2 films having an excess of silicon from 22 to 33 at.% (samples S1, S2, S3, and S4) in the middle SRSN layer, (b) PL energies and intensities of the as-deposited films as a function of silicon excess in the SRSN layer
Mentions: Figure 4a shows the PL spectra of the as-deposited samples. All the samples exhibit broad and strong visible PL at room temperature. The mechanism for strong luminescence from SiNx materials is commonly suggested from the combination of Si/SiNx interface luminescence, gap state luminescence/band-tail luminescence, and luminescence from Si nanodots/clusters. In this investigation, efforts have been made to minimize Si/SiNx interface luminescence with the introduction of high-quality thermal SiO2 before SiNx deposition, which gives rise to enhanced interface quality with minimal interfacial defect states. Details regarding interface traps will be discussed in the C-V analysis part. As evident from Figure 4a,b, with increase in nitrogen content in the SRSN films, the PL peak shifts to higher energies together with an increase in the relative intensity and width. This behavior is commonly attributed to a model based on quantum confinement effect (QCE) [27-29]. From the QCE model point of view, PL blue shift is caused by the reduction in Si-np size, and the increase in emission efficiency can be correlated with the onset of pseudo-direct bandgap behavior. However, no sin-np/cluster has been detected in our EFTEM analysis for these as-deposited SRN films. Thus, the role of QCE can be ruled out. The behavior of PL is in very good agreement with the findings by other authors for a-SiNx:H [30-32] and a-SiCx:H [33,34], where it has been attributed to a model based on band-tail states. In this model, the carriers radiatively recombine with the localized states at the band tails of the gap. With increasing nitrogen content, the bandgap energy increases, which results in a blue shift of the PL energy. However, for band-tail mechanism, the emission generally occurs at energies lower than 1.82 eV [11]. In this study, the peak position of PL spectra is higher than this value, especially for the samples with lower excess of Si. Furthermore, based on Robertson's calculated results [35,36], Ko et al. [37] have proposed possible mechanisms related to defect states to explain PL in silicon nitride films. Being amorphous, the samples have varying optical band gaps depending on composition. Therefore, the energy levels are not well defined. In addition, there is a distribution of states for a given defect giving rise to broad features in the PL spectra. Some investigations have shown both theoretically and experimentally that the PL band with peak positions of 1.8-3.2 eV [38-40] is closely related to the defect states within the bandgap of amorphous SiNx materials. Indeed, large amount of defect-related gap states generally exists in non-stoichiometric silicon nitride layers obtained by CVD process. These defect states having different energy levels contribute to the radiative emission by creating different channels for the relaxation of electronic states. It can be noticed that a weak peak appears around 3.1 eV, whose relative intensity decreases with increasing nitrogen content in the films. Wang et al. have attributed this peak to the presence of nitrogen-dangling bonds [41], whereas others have attributed it to the presence of ≡ Si0 defect sites, which give gap states at 3.1 eV, 80% localized on sites [36]. In this case, as the band becomes prominent at higher Si content, it can be safely assigned to ≡Si0 defect sites rather to than nitrogen-dangling bonds. From the above discussions, it can be ascertained that the predominant mechanism responsible for the PL behavior can be due to the recombination of defect states.

Bottom Line: The silicon-rich a-SiNx:H films (SRSN) were sandwiched between a bottom thermal SiO2 and a top Si3N4 layer, and subsequently annealed within the temperature range of 500-1100°C in N2 to study the effect of annealing temperature on light-emitting and charge storage properties.A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C.A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices.

View Article: PubMed Central - HTML - PubMed

Affiliation: InESS-UdS-CNRS, 23 Rue du Loess, 67037 Strasbourg, France. sahu.bhabani@iness.c-strasbourg.fr.

ABSTRACT
In this study, a wide range of a-SiNx:H films with an excess of silicon (20 to 50%) were prepared with an electron-cyclotron resonance plasma-enhanced chemical vapor deposition system under the flows of NH3 and SiH4. The silicon-rich a-SiNx:H films (SRSN) were sandwiched between a bottom thermal SiO2 and a top Si3N4 layer, and subsequently annealed within the temperature range of 500-1100°C in N2 to study the effect of annealing temperature on light-emitting and charge storage properties. A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C. The possible origins of the PL are briefly discussed. The authors have succeeded in the formation of amorphous Si quantum dots with an average size of about 3 to 3.6 nm by varying excess amount of Si and annealing temperature. Electrical properties have been investigated on Al/Si3N4/SRSN/SiO2/Si structures by capacitance-voltage and conductance-voltage analysis techniques. A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices.

No MeSH data available.