Filtern
Dokumenttyp
- Zeitschriftenartikel (8)
- Beitrag zu einem Tagungsband (7)
- Vortrag (5)
- Posterpräsentation (1)
Schlagworte
- Glass (3)
- Laser processing (3)
- Raman spectroscopy (3)
- XANES (3)
- Doping (2)
- Femtosecond laser (2)
- Magnesium compounds (2)
- Potassium compounds (2)
- Selective emitter (2)
- Bond lengths (1)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (5)
Towards an industrial laser doping process for the selective emitter using phosphoric acid as dopant
(2011)
Different laser supported approaches have already been realized, proving the great potential of laserdoped selective emitters (LDSE). However, it is challenging to establish a low-cost process by using pulsed laser tools. So far a single-step process only leads to satisfying results utilizing cw-lasers. In this paper we have examined a two-step process to produce laser-doped selective emitters on multicrystalline textured standard silicon photovoltaic wafers (90-Ω/sq-Emitter, SiN-antireflection coating (ARC)). The precise ARC removal by near-infrared fs-laser pulses (30 fs, 800 nm), and the doping of uncoated silicon wafers by ns-laser pulses (8 ns, 532 nm) were systematically investigated. In the fs-experiment, optimum conditions for ARC removal were identified. In the nsexperiments under suitable conditions (melting regime), the phosphorous concentration underneath the wafer surface was significantly increased and the sheet resistance was reduced by nearly a factor of two. Moreover, electrical measurements on fired metallization fingers deposited on the laser processed wafers showed low contact resistances. Hence, wafer conditioning with combined fs-laser- and ns-laser-processes are expected to be a promising technology for producing selective emitters.
Towards an industrial laser doping process for the selective emitter using phosphoric acid as dopand
(2011)
Time-resolved phase-contrast microscopy is employed to visualize spatio-temporal thermal transients induced by tight focusing of a single Ti:sapphire fs-laser pulse into a solid dielectric sample. This method relies on the coupling of the refractive index change and the sample temperature through the thermo-optic coefficient dn/dT. The thermal transients are studied on a timescale ranging from 10 ns up to 0.1 ms after laser excitation. Beyond providing direct insights into the laser–matter interaction, analyzing the results obtained also enables quantifying the local thermal diffusivity of the sample on a micrometer scale. Studies conducted in different solid dielectrics, namely amorphous fused silica (a-SiO2), a commercial borosilicate glass (BO33, Schott), and a custom alkaline earth silicate glass (NaSi66), illustrate the applicability of this approach to the investigation of various glassy materials.
Structural relaxation phenomena in binary and multicomponent lithium silicate glasses were studied upon irradiation with femtosecond (fs) laser pulses (800 nm central wavelength, 130 fs pulse duration) and subsequent thermal annealing experiments. Depending on the annealing temperature, micro-Raman spectroscopy analyses evidenced different relaxation behaviours, associated to bridging and non-bridging oxygen structures present in the glass network. The results indicate that the mobility of lithium ions is an important factor during the glass modification with fs-laser pulses. Quantitative phase contrast imaging (spatial light interference microscopy) revealed that these fs-laser induced structural modifications are closely related to local changes in the refractive index of the material. The results establish a promising strategy for tailoring fs-laser sensitivity of glasses through structural mobility.
The effects of single femtosecond laser pulse irradiation (130 fs pulse duration, 800 nm center wavelength) on the structure of binary lithium silicate glasses of varying chemical compositions were investigated by micro-Raman spectroscopy. Permanent modifications were generated at the surface of the glass samples with varying laser fluences in the ablative regime and evaluated for changes in the corresponding Raman band positions and bandwidths. For increasing laser fluences, the position of certain Raman bands changed, indicating an increase in the mass density of the glass inside the irradiated area. Simultaneously, the widths of all investigated bands increased, indicating a higher degree of disorder in the glass structure with respect to bond-angle and bond-length variations.
Silver in LTCC - Interfacial reactions, transport processes and influence on properties of ceramics
(2009)
In this work, glasses with systematically varied compositions were manufactured and irradiated by single Ti:sapphire fs-laserpulses (800 nm, 120 fs), focused at the surface and into the bulk of the glass materials. The samples were tested for their ablation threshold fluence as well as for structural changes using µ-Raman-spectroscopy. Correlations between the glass composition, the material-ablation on the glass surface and the permanent changes of the refractive index inside the glass volume after the irradiation by fs-laser pulses were obtained. The results show, that the structural modifications found at the surface of the glasses and inside its volume are closely related. However, while the ablation threshold fluence of the glass surface primarily depends on the glass dissociation energy, the permanent refractive index change inside the volume is rather determined by its ability for absorbing the fs-laser pulses and the subsequent relaxation processes. The results of this work provide some guidance on how the glass composition can be varied in order to optimize the fs-laser induced modification of dielectrics.
Over the past years, many applications based on laser-induced refractive index changes in the volume of transparent materials have been demonstrated. Ultrashort pulse lasers offer the possibility to process bulky transparent materials in three dimensions, suggesting that direct laser writing will play a decisive role in the development of integrated micro-optics. At the present time, applications such as 3D long term data storage or embedded laser marking are already into the phase of industrial development. However, a quantitative estimate of the laser-induced refractive index change is still very challenging to obtain. On another hand, several microscopy techniques have been recently developed to characterize bulk refractive index changes in-situ. They have been mostly applied to biological purposes. Among those, spatial light interference microscopy (SLIM), offers a very good robustness with minimal post acquisition data processing. In this paper, we report on using SLIM to measure fs-laser induced refractive index changes in different common glassy materials, such as fused silica and borofloat glass (B33). The advantages of SLIM over classical phase-contrast microscopy are discussed.