Doping of germanium by ion-implantation and laser annealing in the melting regime

Germanium is the main candidate for replacing silicon in active regions in future complementary metal-oxide transistors due to: (i) its higher mobility of charge carriers that makes it able to attain higher drive current; (ii) the availability of high-k materials, excellent substitutes for its unstable native oxide and (iii) its lower melting point that allows lower processing temperatures. However, a downscaling beyond 15-nm necessarily requires higher doping levels (higher than 1x10^20cm^-3) beyond the solid solubility of most of the dopants. In particular, n-type ultra-shallow junctions (USJs) are the most challenging, because of the lower solid solubility and higher diffusivity of V-group elements in Ge which make the required shallow doping profiles hard to achieve. For these reasons, laser thermal annealing (LTA) in the melting regime is a promising advanced activation technology of implanted dopants in Ge for USJs formation. In fact, it has a potential capability of increasing the dopant solubility as well as of confining the diffusion processes into the molten layer, whose depth can be controlled by choosing adequate energy density in turn. Thanks to this technique, donor concentration far exceeding the theoretical maximum solid solubility limits after LTA in Ge are reported in literature for implanted phosphorous and antimony, pushing the doping limits for these systems above to 1x10^21cm^-3. Despite the above encouraging results, melting LTA on Ge doped with arsenic as well as with acceptors was still unexplored. Therefore, the aim of this work was the investigation of the LTA process applied to both the n-type and p-type doping of Ge after arsenic or boron implantation. In particular, experiments on diffusion, contamination, thermal stability, residual strain and clustering were performed in order to study mechanisms influencing the resulting electrical activation

Low temperature deactivation of Ge heavily n-type doped by ion implantation and laser thermal annealing

International audienceHeavy doping of Ge is crucial for several advanced micro-and optoelectronic applications, but, at the same time, it still remains extremely challenging. Ge heavily n-type doped at a concentration of 1 X 10(20) cm(-3) by As ion implantation and melting laser thermal annealing (LTA) is shown here to be highly metastable. Upon post-LTA conventional thermal annealing As electrically deactivates already at 350 degrees C reaching an active concentration of similar to 4 x 10(19) cm(-3). No significant As diffusion is detected up to 450 degrees C, where the As activation decreases further to similar to 3 x 10(19) cm(-3). The reason for the observed detrimental deactivation was investigated by Atom Probe Tomography and in situ High Resolution X-Ray Diffraction measurements. In general, the thermal stability of heavily doped Ge layers needs to be carefully evaluated because, as shown here, deactivation might occur at very low temperatures, close to those required for low resistivity Ohmic contacting of n-type Ge

Heavily-doped Germanium on Silicon with Activated Doping Exceeding 1020 cm−3 as an Alternative to Gold for Mid-infrared Plasmonics

Ge-on-Si has been demonstrated as a platform for Si foundry compatible plasmonics. We use laser thermal annealing to demonstrate activated doping levels >1020 cm-3 which allows most of the 3 to 20 μm mid-infrared sensing window to be covered with enhancements comparable to gold plasmonics

Chalcogen-hyperdoped germanium for short-wavelength infrared photodetection

Obtaining short-wavelength-infrared (SWIR; 1.4 μm–3.0 μm) room-temperature photodetection in a low-cost, group IV semiconductor is desirable for numerous applications. We demonstrate a non-equilibrium method for hyperdoping germanium with selenium or tellurium for dopant-mediated SWIR photodetection. By ion-implanting Se or Te into Ge wafers and restoring crystallinity with pulsed laser melting induced rapid solidification, we obtain single crystalline materials with peak Se and Te concentrations of 1020 cm−3 (104 times the solubility limits). These hyperdoped materials exhibit sub-bandgap absorption of light up to wavelengths of at least 3.0 μm, with their sub-bandgap optical absorption coefficients comparable to those of commercial SWIR photodetection materials. Although previous studies of Ge-based photodetectors have reported a sub-bandgap optoelectronic response only at low temperature, we report room-temperature sub-bandgap SWIR photodetection at wavelengths as long as 3.0 μm from rudimentary hyperdoped Ge:Se and Ge:Te photodetectors

Gold-hyperdoped Germanium with Room-Temperature Sub-bandgap Optoelectronic Response

Hyperdoping germanium with gold is a potential method to produce room-temperature short-wavelength-infrared radiation (SWIR; 1.4–3.0μm) photodetection. We investigate the charge carrier dynamics, light absorption, and structural properties of gold-hyperdoped germanium (Ge:Au) fabricated with varying ion implantation and nanosecond pulsed laser melting conditions. Time-resolved terahertz spectroscopy (TRTS) measurements show that Ge:Au carrier lifetime is significantly higher than that in previously studied hyperdoped silicon systems. Furthermore, we find that lattice composition, sub-band-gap optical absorption, and carrier dynamics depend greatly on hyperdoping conditions. We use density functional theory (DFT) to model dopant distribution, electronic band structure, and optical absorption. These simulations help explain experimentally observed differences in optical and optoelectronic behavior across different samples. DFT modeling reveals that substitutional dopant incorporation has the lowest formation energy and leads to deep energy levels. In contrast, interstitial or dopant-vacancy complex incorporation yields shallower energy levels that do not contribute to sub-band-gap light absorption and have a small effect on charge carrier lifetimes. These results suggest that it is promising to tailor dopant incorporation sites of Ge:Au for SWIR photodetection applications

Overview on electrical issues faced during the SPIDER experimental campaigns

SPIDER is the full-scale prototype of the ion source of the ITER Heating Neutral Beam Injector, where negative ions of Hydrogen or Deuterium are produced by a RF generated plasma and accelerated with a set of grids up to ~100 keV. The Power Supply System is composed of high voltage dc power supplies capable of handling frequent grid breakdowns, high current dc generators for the magnetic filter field and RF generators for the plasma generation. During the first 3 years of SPIDER operation different electrical issues were discovered, understood and addressed thanks to deep analyses of the experimental results supported by modelling activities. The paper gives an overview on the observed phenomena and relevant analyses to understand them, on the effectiveness of the short-term modifications provided to SPIDER to face the encountered issues and on the design principle of long-term solutions to be introduced during the currently ongoing long shutdown.Comment: 8 pages, 12 figures. Presented at SOFT 202

Doping of germanium by ion-implantation and laser annealing in the melting regime

Germanium is the main candidate for replacing silicon in active regions in future complementary metal-oxide transistors due to: (i) its higher mobility of charge carriers that makes it able to attain higher drive current; (ii) the availability of high-k materials, excellent substitutes for its unstable native oxide and (iii) its lower melting point that allows lower processing temperatures. However, a downscaling beyond 15-nm necessarily requires higher doping levels (higher than 1x10^20cm^-3) beyond the solid solubility of most of the dopants. In particular, n-type ultra-shallow junctions (USJs) are the most challenging, because of the lower solid solubility and higher diffusivity of V-group elements in Ge which make the required shallow doping profiles hard to achieve. For these reasons, laser thermal annealing (LTA) in the melting regime is a promising advanced activation technology of implanted dopants in Ge for USJs formation. In fact, it has a potential capability of increasing the dopant solubility as well as of confining the diffusion processes into the molten layer, whose depth can be controlled by choosing adequate energy density in turn. Thanks to this technique, donor concentration far exceeding the theoretical maximum solid solubility limits after LTA in Ge are reported in literature for implanted phosphorous and antimony, pushing the doping limits for these systems above to 1x10^21cm^-3. Despite the above encouraging results, melting LTA on Ge doped with arsenic as well as with acceptors was still unexplored. Therefore, the aim of this work was the investigation of the LTA process applied to both the n-type and p-type doping of Ge after arsenic or boron implantation. In particular, experiments on diffusion, contamination, thermal stability, residual strain and clustering were performed in order to study mechanisms influencing the resulting electrical activation.Il germanio è il principale candidato a sostituire il silicio come substrato per i futuri dispositivi elettronici ultra-scalati, poiché: (i) la sua superiore mobilità di portatori di carica consente correnti maggiori; (ii) la possibilità di crescere ossidi alternativi ad alta capacità dielettrica (high-k), consente di aggirare i problemi legati all’ossido nativo e (iii) la sua minore temperatura di fusione lo rende più facilmente processabile. Tuttavia, miniaturizzazioni che soddisfano i futuri nodi tecnologici (in particolare al di sotto dei 15-nm) necessariamente richiedono livelli di drogaggio più alti di 1x10^20cm^-3, oltre cioè le solubilità solide della maggior parte dei droganti. In particolare, le più problematiche sono le giunzioni ultra-sottili (USJ) di tipo-n, date le basse solubilità e le alte diffusività degli elementi del V gruppo in Ge che rendono gli alti livelli di drogaggio richiesti ardui da ottenere. A questo scopo, il laser thermal annealing (LTA) in regime di fusione rappresenta una promettente avanzata tecnologia di attivazione elettrica dei droganti impiantati, data la sua potenziali capacità di aumentare le solubilità dei droganti, conseguente alla rapidissima ricrescita epitassiale da fase liquida (LPER) indotta, e di confinare i processi diffusivi nella regione liquefatta, la quale viene a sua volta controllata, modulando opportunamente la densità d’energia. Grazie a questa tecnica si sono infatti ottenute in Ge concentrazioni attive che superano ampiamente le rispettive solubilità solide, sia di fosforo impiantato che di antimonio dove si è ottenuto l’impressionante record di 1x10^21cm^-3. Nonostante questi incoraggianti risultati, il LTA nel caso di Ge drogato con arsenico o con accettori non è stato ancora sperimentato. Inoltre, quanto si impiantano grandi fluenze di droganti, si ottengono solo parziali attivazioni elettriche e una profonda comprensione della fenomenologia che avviene durante una così estrema LPER è ancora mancante. Perciò, lo scopo di questo lavoro è stato lo studio del processo di LTA applicato sia per drogaggio di tipo-n che –p di Ge dopo l’impianto di arsenico o boro. In particolare si sono svolti esperimenti svolti sulla diffusione, contaminazione, stabilità termica, stato di deformazione residuo e formazione di clusters al fine di studiarne l’influenza sulla attivazione elettrica risultante

Design and Verification of Long-Running Transactions in a Timed Framework

Long–running transactions consist of tasks which may be executed sequentially and in parallel, may contain sub–tasks, and may require to be completed before a deadline. These transactions are not atomic and, in case of executions which cannot be completed, a compensation mechanism must be provided. In this paper we develop a model of Communicating Hierarchical Timed Automata suitable to describe the mentioned aspects in a framework where also time is taken into account. We develop the patterns for composing long–running transactions sequentially, in parallel or by nesting. The correct compensation of a composed long–running transaction is preserved by these composition patterns. The automaton-theoretic approach allows the verification of properties by model checking. As a case study, we model and analyse an example of e–commerce application described in terms of long–running transactions

Modeling Long--Running Transactions with

Long-Running transactions consist of tasks which may be executed sequentially and in parallel, may contain sub-tasks, and may require to be completed before a deadline. These transactions are not atomic and, in case of executions which cannot be completed, a compensation mechanism must be provided