Analysis and optimization of propagation losses in LiNbO3 optical waveguides produced by swift heavy-ion irradiation

The propagation losses (PL) of lithium niobate optical planar waveguides fabricated by swift heavy-ion irradiation (SHI), an alternative to conventional ion implantation, have been investigated and optimized. For waveguide fabrication, congruently melting LiNbO3 substrates were irradiated with F ions at 20 MeV or 30 MeV and fluences in the range 1013–1014 cm−2. The influence of the temperature and time of post-irradiation annealing treatments has been systematically studied. Optimum propagation losses lower than 0.5 dB/cm have been obtained for both TE and TM modes, after a two-stage annealing treatment at 350 and 375∘C. Possible loss mechanisms are discussed

Recrystallization of amorphous nano-tracks and uniform layers generated by swift-ion-beam irradiation in lithium niobate.

The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO3) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<1012 cm−2) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3×1011 cm−2 and 1012 cm−2. The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphous-crystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ∼1014 cm−2. Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystalline-amorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed

APPLICATIONS OF TRANSIENT ANNEALING TO SOLAR CELL PROCESSING

Les raisons économiques justifiant l'introduction de les requits à transient dans la fabrication de les cellules solaires ont été brièvement discuté. Ces techniques peuvent jouer un rôle important dans la production à grande échelle, pour leur compatibilité avec la demande de procédés automatiques, associé à une bonne qualité de la jonction p-n. Les applications des différents techniques de recuite à transient appliquées à la production des cellules solaires ont été discuté en comparant les résultats obtenues, soit en phase liquide soit en phase solide, après Implantation Ionique ou déposition du dopant sur la surface. La possibilité de réalisation de jonction p-n à la suite de une impulsion laser donné en une atmosphère contenant un gaz dopant, sera brièvement présenté.The economical reasons supporting the introduction of transient annealing in solar cell manufacturing are briefly discussed. Such techniques may play an important role, as they are compatible with the request of high throughput, automated processing together with the high quality of the p-n junction which are necessary for large scale economical production of photovoltaic energy. A survey of the applications of the different transient annealing techniques to solar cell processing has been developed by comparing in detail the results obtained up to now the case of solid and liquid phase transient annealing, associated with dry techniques such as Ion Implantation or dopant deposition on the wafer surface. The possibility of using laser pulses for the formation of the p-n junction by incorporation of dopant atoms from a suitable gaseous environment, has also been examined

NATIVE OXIDES BEHAVIOR DURING PULSED LASER IRRADIATION OF GaAs

Nous avons utilisé des techniques d'analyses nucléaires et de spectrométrie de masse d'ions secondaires pour étudier le comportement d'oxydes natifs de GaAs enrichis à l'18O et irradiés sous vide au moyen d'un laser à Rubis déclenché. Nous avons examiné l'incorporation d'16O, l'incorporation et les pertes d'18O ainsi que le déplacement des cations As et Ga hors des sites du réseau en fonction de la densité d'énergie du faisceau laser. Nos résultats démontrent qu'il est nécessaire d'irradier avec une densité d'énergie de l'ordre de 0,8 J/cm2, afin d'éliminer complètement les oxydes de surface. Toutefois, avant élimination complète, nous observons une dissolution partielle de ces oxydes dans le matériau liquide sous-jacent, ce qui a pour effet d'induire un important piégeage d'oxygène dans les couches resolidifiées. Nous observons de plus que la surface passe de façon continue d'un état riche en Ga à un état riche en As, tandis que la densité d'énergie du faisceau laser croît de 0,4 J/cm2 à 1 J/cm2.Nuclear Microanalysis and Secondary Ion Mass Spectroscopy have been used to study the behavior of GaAs 18O enriched native oxides irradiated with a pulsed Ruby laser under vacuum. We have analyzed 16O incorporation, 18O losses and incorporation and Ga and As atoms out of crystallographic sites as a function of laser energy density. Our results demonstrate that an energy density of 0.8 J/cm2 is needed to completely remove the native oxides. However, before complete evaporation, part of these oxides are dissolved in the layer melted by the laser pulse, leading to oxygen trapping in the resolidified material. We also find that the surface composition varies continuously from Ga rich to As rich when the laser energy density is raised from 0.4 J/cm2 up to 1 3/cm2

EFFECT OF OXYGEN PRESSURE ON OXYGEN INCORPORATION IN Si AND Ga As DURING Q SWITCHED LASER IRRADIATION

Nous avons étudié l'incorporation d'oxygène et sa relation avec la stabilité de l'oxyde de surface dans des échantillons d'Arseniure de Gallium et de silicium, soumis à des irradiations laser pulsées (≈ 15 ns) intenses (≈ 1 J/cm2), dans le visible, sous fortes pressions d'oxygène. A cet effet, nous avons utilisé la microanalyse nucléaire (rétrodiffusion, réactions nucléaires, canalisation) et des techniques de traçage isotopique à l'18O. Dans le cas de Ga As il existe un seuil de densité d'énergie (Eth ≥ ~ 1.1 J/cm2) au-dessus duquel se produit une forte incorporation d'oxygène. Cette incorporation est pratiquement proportionnelle à la pression du gaz. Des résultats similaires sont observés pour Si, mais dans ce cas la reproductivité est mauvaise. Le rôle de l'oxyde de surface a été mis en évidence en étudiant des échantillons recouverts d'une mince couche d'oxyde enrichie en 18O (= 100 Å), formée par oxydation anodique. On constate dans le cas de Ga As une importante perte d'18O pour des irradiations au-dessus du seuil Eth correspondant à l'incorporation. La relation entre cette dernière et la destruction de l'oxyde de surface est discutée.Nuclear microanalysis (R.B.S., Nuclear reactions, channeling) combined with 18O tracing techniques have been used to study oxygen incorporation and native oxide stability for Ga As and Si submitted to intense pulse laser irradiation under high oxygen pressure (pulse duration = 15 ns of either Ruby or frequency doubled Nd:YAG laser). We have found an energy threshold for Ga As (Eth ≥ ~ 1.1 J/cm2) above which an important oxygen uptake is observed during laser irradiation. The oxygen incorporation for pulse laser energy density E > Eth is a quasi linear function of oxygen pressure. Similar results have been found for Si although an important scattering in experimental results is observed. The role of native oxide films has been studied by using samples covered with thin (~ 100 Å) 18O enriched surface oxide layers. We have found (for Ga As) that for E > Eth 18O is lost. The possible relation between the oxygen uptake (16O) from gas phase and the loss of native oxide is discussed