UV to NIR photon conversion in Nd-doped rutile and anatase titanium dioxide films for silicon solar cell application

Undoped and Nd-doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700 °C under 0.1 mbar O2. By selecting adequate substrates, TiO2 films doped with 1, 2 or 5 at.% Nd were grown and constituted with polycrystalline rutile, highly oriented (2 0 0) rutile film, or oriented (0 0 4) anatase. An UV to NIR photon conversion is evidenced in the films. Indeed, intense and well-resolved emission lines from Nd3+ have been observed upon excitation above the TiO2 bandgap at room temperature. The sensitised emission of Nd3+ is found to be much efficient in rutile than in anatase structure. Low temperature photoluminescence measurements lead to fine resolved peaks corresponding to the Nd3+ 4f transitions with different spectral characteristic according to the host matrix used. Photoluminescence dependence temperature evidences that the light emission from Nd3+ in anatase-based films is probably influenced by the presence of self-trapped excitons or by orbital interaction. Mechanisms of sensitisation host to Nd3+ are proposed for both matrixes. Finally, the Nd dopant concentration and the microstructure of TiO2 rutile films are found to affect the photoluminescence emission intensity. Rutile film (2 0 0) oriented is the most adapted host matrix to sensitise 1 at.% Nd3+ ions for an emission around 1064 nm making such Nd-doped layers interesting for photon conversion by down shifting process

Structural and nuclear characterizations of defects created by noble gas implantation in silicon oxide

Thermally grown silicon oxide layer was implanted at room temperature with 300keV Xe at fluences ranging from 0.5 to 5x10$^16$Xe/cm$^2$. Bubbles created after Xe-implantation provided a low-k silicon oxide that has potential use as a dielectric material for interconnects in Si integrated circuits. Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry (RBS) and Positron Annihilation Spectroscopy (PAS) were used to provide a comprehensive characterization of defects (bubbles, vacancy, gas atoms and other types of defects) created by Xe implantation in $SiO_2$ layer. These measurements suggest that the bubbles observed with TEM for all fluences were a consequence of the interaction between Xe and vacancies (V), with $V_nXe_m$ complexes created in the zone where V and Xe profiles overlap. Negatively charged defects such as ($Si-O^-$, $Si-O-O^-$ and $O_2^-$) are also created after implantation

UV to NIR photon conversion in Nd-doped rutile and anatase titanium dioxide films for silicon solar cell application

Undoped and Nd-doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700 °C under 0.1 mbar O2. By selecting adequate substrates, TiO2 films doped with 1, 2 or 5 at.% Nd were grown and constituted with polycrystalline rutile, highly oriented (2 0 0) rutile film, or oriented (0 0 4) anatase. An UV to NIR photon conversion is evidenced in the films. Indeed, intense and well-resolved emission lines from Nd3+ have been observed upon excitation above the TiO2 bandgap at room temperature. The sensitised emission of Nd3+ is found to be much efficient in rutile than in anatase structure. Low temperature photoluminescence measurements lead to fine resolved peaks corresponding to the Nd3+ 4f transitions with different spectral characteristic according to the host matrix used. Photoluminescence dependence temperature evidences that the light emission from Nd3+ in anatase-based films is probably influenced by the presence of self-trapped excitons or by orbital interaction. Mechanisms of sensitisation host to Nd3+ are proposed for both matrixes. Finally, the Nd dopant concentration and the microstructure of TiO2 rutile films are found to affect the photoluminescence emission intensity. Rutile film (2 0 0) oriented is the most adapted host matrix to sensitise 1 at.% Nd3+ ions for an emission around 1064 nm making such Nd-doped layers interesting for photon conversion by down shifting process

The role of a top oxide layer in cavities formed by MeV He implantation into Si

In this paper, we report the results on the influence of a top oxide layer on the He-cavity formation in silicon samples. Si samples with top oxide layers of different thickness together with the pure silicon (used as reference) were implanted at room temperature with 1 MeV 3He at a dose of 5 × 1016 He/cm2. After implantation, the oxide layer was removed by using HF solution. Cross-sectional transmission electron microscopy (XTEM) was used to study the induced cavities followed by annealing. The results show that He implantation induces a well-defined-damaged layer with a thickness of about 180 nm in the reference Si. The defects are mainly made up of big cavities in the middle of the projected range and a large population of smaller ones both towards the surface and into the bulk. Very few stacking faults and dislocations loops can be seen around this band. The creation of cavities in Si with a 2.3 μm oxide layer, however, is a little different. Regions containing a chain of the biggest cavities surrounded by few smaller ones have also been found. Unexpected results are obtained in Si with a 1.2 μm oxide layer. In this case, only a monolayer of big cavities is observed at the depth corresponding to the projected range. The results are discussed in combination with SIMS measurements and SRIM simulations

Modification of SiO2 by Kr and Xe implantations

International audienc

Synthesis of mesoporous amorphous silica by Kr and Xe ion implantation: Transmission electron microscopy study of induced nanostructures

Thermally grown amorphous SiO2 was implanted at room temperature with heavy noble gases Kr and Xe in order to create cavities in the oxide and increase its porosity. The implantation energies were chosen in order to have the same implantation depth for both ions. Although both ions induce bubbles in amorphous SiO2, bubble size and spatial distribution depend upon the ion mass. Moreover, Xe implantation leads to the additional formation of "nanoclusters". Thermal stability of bubbles/cavities depends on the implanted ion. The nucleation of bubbles and nanoclusters in amorphous SiO2 is discussed in terms of ion mobility, gas-defect interactions, and chemical interaction. Bubble growth is shown to occur by a migration and coalescence process

Structural and optical characterization of a dispersion of nanocavities in a crystalline silicon matrix

FZ silicon samples were multi-implanted with He ions at energies ranging from 0.8 MeV to 1.9 MeV. The dose was 5×1016 He cm−2 for all high energies but 0.8 MeV (3×1016 He cm−2). After implantation, the wafers were submitted to different annealing processes in an Argon atmosphere (A samples: 900 °C and 700 °C for 2 h; B sample 550 °C for 14 h) to optimize both density and size of cavities in order to reach a structure potentially light emitting like that of porous silicon. The samples were studied by cross section transmission electron microscopy (XTEM) and photoluminescence spectroscopy. XTEM results showed that a very thick region containing cavities has been obtained by a multi step implantation and that an annealing at low temperature is sufficient to recover the implantation damage. PL spectra arising from different depths have been obtained. PL results confirm that silicon in the region containing the highest density of cavities remains crystalline with a sufficiently low defect density for optoelectronic applications