Browsing by Author "Slotte, Jonatan"
Now showing 1 - 19 of 19
Results Per Page
Sort Options
Item A demonstration of donor passivation through direct formation of V-As_i complexes in As-doped Ge_1−xSn_x(American Institute of Physics, 2020-05-21) Khanam, Afrina; Vohra, Anurag; Slotte, Jonatan; Makkonen, Ilja; Loo, Roger; Pourtois, Geoffrey; Department of Applied Physics; Antimatter and Nuclear Engineering; IMEC Vzw; University of Antwerp; KU Leuven; University of HelsinkiPositron annihilation spectroscopy in the Doppler and coincidence Doppler mode was applied on Ge_1−xSn_x epitaxial layers, grown by chemical vapor deposition with different total As concentrations (∼10^19–10^21 cm−3), high active As concentrations (∼10^19 cm−3), and similar Sn concentrations (5.9%–6.4%). Positron traps are identified as mono-vacancy complexes. Vacancy-As complexes, V-As_i, formed during the growth were studied to deepen the understanding of the electrical passivation of the Ge_1−xSn_x:As epilayers. Larger mono-vacancy complexes, V-As_i (i≥2), are formed as the As doping increases. The total As concentration shows a significant impact on the saturation of the number of As atoms (i=4) around the vacancies in the sample epilayers. The presence of V-As_i complexes decreases the dopant activation in the Ge_1−xSn_x:As epilayers. Furthermore, the presence of Sn failed to hinder the formation of larger V-As_i complexes and thus failed to reduce the donor-deactivationItem Divacancy clustering in neutron-irradiated and annealed n-type germanium(2008-07) Kuitunen, Katja; Tuomisto, Filip; Slotte, Jonatan; Capan, Ivana; Department of Applied Physics; Antimatter and Nuclear EngineeringWe have studied the annealing of vacancy defects in neutron-irradiated germanium. After irradiation, the Sb-doped samples [(Sb)=1.5×1015 cm−3] were annealed at 473, 673, and 773 K for 30 min. The positron lifetime was measured as a function of temperature (30–295 K). A lifetime component of 330 ps with no temperature dependence is observed in as-irradiated samples, identified as the positron lifetime in a neutral divacancy and indicating that the divacancy is stable at room temperature (RT). Annealing at 673 K resulted in an increase in the average positron lifetime, and in addition, the annealed samples further showed a larger lifetime component of 430 ps at RT, which is due to larger vacancy clusters. The average positron lifetime in the samples annealed at 473 K has a definite temperature dependence, suggesting that the divacancies become negative as the crystal recovers and the Fermi level moves upwards in the band gap. Annealing at 673 K, reduces the average lifetime and intensity of the defect component τ2 at RT, indicating that the vacancy clusters have started to anneal. Negative divacancies are still present in the samples after this anneal. Annealing at 773 K is enough to remove all observable vacancy defects.Item Electrical and Electro-Optical Characterization of Ultra-Wide Band Gap Semiconductors Devices(2021-08-24) Faure, Camille; Ferrandis, Philippe; Perustieteiden korkeakoulu; Slotte, JonatanDue to the increasing use of new energies and new ways of transportation, the electric grid requires novel power devices that allow energy to be saved. Among semiconductors, diamond is one of the promising materials that is well known to overpass the current silicon semiconductor due to its physical properties better suited for high power application. This paper aims to study and understand the electrically active defects present in recent diamond power devices, such as Schottky diodes or Metal Semiconductor Field Effect Transistors (MESFET). These defects can be created during the manufacturing steps and impact the electrical performances of the component. To characterize the potential defects present in the device, we mainly used two methods: Thermal Admittance Spectroscopy (TAS) and Deep Level Transient Spectroscopy (DLTS). Two components were studied by using the previous methods and other simple electrical measurements, a Schottky diode and a MESFET. Regarding the diode, the results showed no defects except boron with an activation energy of 0.34 eV and a capture cross section of 7×10-12 cm-2 determined by TAS. Concerning the transistor, DLTS and current-voltage measurements revealed a potential activation by light or thermal energy of the pn-junction between the channel and the 1b diamond substrate. Further investigations on the junction also indicated the presence of a conductive layer situated on the side of the sample, that could have affected the previous experiments. These results suggest that well-designed diamond components can contain only a few defects similarly to the diode. The results also demonstrate that the substrate-channel pn-junction or diamond growth on the side of the component can impact its functioning and should be considered when designing the device.Item Epäpuhtausatomien laser-aktivoinnin vaikutus vakanssivirheisiin vahvasti n-seostetussa germaniumissa(2015-09-03) Kalliovaara, Tuomas; Slotte, Jonatan; Perustieteiden korkeakoulu; Tuomisto, FilipItem Evolution of phosphorus-vacancy clusters in epitaxial germanium(AIP Publishing, 2019-01-14) Vohra, Anurag; Khanam, Afrina; Slotte, Jonatan; Makkonen, Ilja; Pourtois, Geoffrey; Loo, Roger; Vandervorst, Wilfried; KU Leuven; Department of Applied Physics; Antimatter and Nuclear Engineering; IMEC VzwThe E centers (dopant-vacancy pairs) play a significant role in dopant deactivation in semiconductors. In order to gain insight into dopant-defect interactions during epitaxial growth of in situ phosphorus doped Ge, positron annihilation spectroscopy, which is sensitive to open-volume defects, was performed on Ge layers grown by chemical vapor deposition with different concentrations of phosphorus (∼ 1 × 10 18- 1 × 10 20 cm - 3). Experimental results supported by first-principles calculations based on the two component density-functional theory gave evidence for the existence of mono-vacancies decorated by several phosphorus atoms as the dominant defect type in the epitaxial Ge. The concentration of vacancies increases with the amount of P-doping. The number of P atoms around the vacancy also increases, depending on the P concentration. The evolution of P n-V clusters in Ge contributes significantly to the dopant deactivation.Item Faradays lag i gymnasiet och på grundkurser vid tekniska universitet(2015-11-30) Smeds, Mathias; Slotte, Jonatan; Perustieteiden korkeakoulu; Alava, MikkoItem Formation and dissociation of defect complexes in heavily Zn doped InP(2004) Holopainen, Silja; Slotte, Jonatan; Teknillisen fysiikan ja matematiikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Saarinen, KimmoItem Germaniumnanokiteiden karakterisointi positroniannihilaatiospektroskopialla(2017-08-22) Kalliovaara, Tuomas; Slotte, Jonatan; Perustieteiden korkeakoulu; Tuomisto, FilipPositroniannihilaatiospektroskopia (PAS) on käytännöllinen menetelmä havainnoida kiinteän aineen vakanssityyppisiä defektejä eli puuttuvien atomien muodostamia hilavirheitä kiderakenteeseen vaikuttamatta. PAS:lla tutkitaan erityisesti puolijohteita, joissa defektit vaikuttavat aineen sähköisiin ja optisiin ominaisuuksiin. Menetelmä perustuu positronien taipumukseen loukkuuntua vakansseihin, joissa elektronien liikemääräjakauma poikkeaa virheettömästä kiteestä, mikä havaitaan muutoksina annihilaatiosäteilyn Doppler-leventyneessä spektrissä. Tässä työssä PAS-mittauksia sovellettiin eristehilaan syntetisoitujen Ge-nanokiteiden ja niiden defektien tutkimiseen. Näytteet oli valmistettu Freibergin yliopistossa Saksassa sputterointitekniikalla ja eri lämpötiloissa toivuttamalla, erityisenä sovelluskohteenaan flash-muistit. Flash-muisteissa datakatoa aiheuttavia vuotovirtoja voidaan vähentää merkittävästi korvaamalla perinteisen teknologian yhtenäinen kelluva hila eristeeseen upotetuilla diskreeteillä nanokiteillä. Pidemmän datan säilyvyyden lisäksi nanokidemateriaaleja hyödyntämällä voidaan madaltaa käyttöjännitteitä ja saavuttaa entistä pienempi mittakaava eli suurempi bittitiheys. Nanokiteiden ja/tai niitä ympäröivän eristeen rakenteessa todettiin huomattavia eroja riippuen kiteiden kasvatukseen käytetystä lämpötilasta. Zirkoniumdioksidiin (ZrO2) kasvatettujen nanokiteiden tapauksessa saatiin viitteitä siitä, että korkeampi kasvatuslämpötila lisää avoimen tilavuuden defektejä atomihilassa. Tantaalilla seostetun ZrO2:n ympäröimillä kiteillä suuntaus oli päinvastainen. Mitattujen annihilaatiospektrien piirteitä ei kuitenkaan voitu varmuudella yhdistää juuri nanokiteisiin tai niiden defekteihin, vaan tyydyttiin toteamaan tarve jatkotutkimuksiin erikokoisilla ja kokojakaumaltaan paremmin määritellyillä nanokiteillä.Item He implantation to control B diffusion in crystalline and preamorphized Si(2008) Bruno, Elena; Mirabella, Salvo; Priolo, Francesco; Kuitunen, Katja; Tuomisto, Filip; Slotte, Jonatan; Giannazzo, Filippo; Bongiorno, Corrado; Raineri, Vito; Napolitani, Enrico; Department of Applied PhysicsWe demonstrate that He can be a powerful tool to control B diffusion both in crystalline (c-Si) and preamorphized Si (PA-Si). By means of positron annihilation spectroscopy (PAS), we showed in He-implanted c-Si the formation after annealing of large open-volume defects at the implant projected range Rp of He (voids) and of smaller vacancy-type defects toward the surface (nanovoids). In particular, these nanovoids locally suppress the amount of self-interstitials (Is) generated by B implantation, as verified by PAS, eventually reducing B diffusion and leading to a boxlike shape of the B-implanted profile. On the other hand, for B implantation in PA-Si, the authors demonstrated that if He-induced voids are formed between the end-of-range (EOR) defects and the surface, they act as a diffusion barrier for Is coming from the EOR defects. Indeed, this barrier strongly reduces diffusion of B placed in proximity of the surface.Item Heavily phosphorus doped germanium:Strong interaction of phosphorus with vacancies and impact of tin alloying on doping activation(AMER INST PHYSICS, 2019-06-14) Vohra, Anurag; Khanam, Afrina; Slotte, Jonatan; Makkonen, Ilja; Pourtois, Geoffrey; Porret, Clement; Loo, Roger; Vandervorst, Wilfried; Department of Applied Physics; Antimatter and Nuclear Engineering; IMEC Vzw; KU LeuvenWe examined the vacancy trapping proficiency of Sn and P atoms in germanium using positron annihilation spectroscopy measurements, sensitive to the open-volume defects. Epitaxial Ge 1 - xSn x films were grown by chemical vapor deposition with different P concentrations in the ∼ 3.0 × 10 19- 1.5 × 10 20 cm - 3 range. We corroborate our findings with first principles simulations. Codoping of Ge with a Sn concentration of up to 9% is not an efficient method to suppress the free vacancy concentration and the formation of larger phosphorus-vacancy complexes. Experimental results confirm an increase in the number of P atoms around the monovacancy with P-doping, leading to dopant deactivation in epitaxial germanium-tin layers with similar Sn content. Vice versa, no impact on the improvement of maximum achieved P activation in Ge with increasing Sn-doping has been observed. Theoretical calculations also confirm that P n-V (vacancy) complexes are energetically more stable than the corresponding Sn mP n-V and Sn m-V defect structures with the same number of alien atoms (Sn or P) around the monovacancy. The strong attraction of vacancies to the phosphorus atoms remains the dominant dopant deactivation mechanism in Ge as well as in Ge 1 - xSn x.Item In Situ Positron Annihilation Spectroscopy Analysis on Low-Temperature Irradiated Semiconductors, Challenges and Possibilities(WILEY-V C H VERLAG GMBH, 2021-01) Slotte, Jonatan; Kilpeläinen, Simo; Segercrantz, Natalie; Mizohata, Kenichiro; Räisänen, Jyrki; Tuomisto, Filip; Department of Applied Physics; Antimatter and Nuclear Engineering; University of HelsinkiA unique experimental setup at the Accelerator Laboratory of the University of Helsinki enables in situ positron annihilation spectroscopy (PAS) analysis on ion irradiated samples. In addition, the system enables temperature control (10–300 K) of the sample both during irradiation and during subsequent positron annihilation measurements. Using such a system for defect identification and annealing studies comes with a plethora of possibilities for elaborate studies. However, the system also poses some restrictions and challenges to these possibilities, both related to irradiation and to the PAS analysis. This review tries to address these issues.Item Influence of silicon doping on vacancies and optical properties of Al(x)Ga(1-x)N thin films(2007) Slotte, Jonatan; Tuomisto, Filip; Saarinen, K.; Moe, C.G.; Keller, Stacia; DenBaars, S.P.; Department of Applied Physics; Antimatter and Nuclear EngineeringThe authors have used positron annihilation spectroscopy and photoluminescence measurements to study the influence of silicon doping on vacancy formation in AlGaN:Si structures. The results show a correlation between the Doppler broadening measurements and the intensity from 510nm photoluminescence transition. The reduction in the W parameter when the [Si]∕[Al+Ga] fraction in the gas phase is above 3×10−4 indicates that the positrons annihilate in an environment where less Ga 3d electrons are present, i.e., they are trapped in group-III vacancies. The observation of vacancies at these silicon concentrations coincides with the onset of the photoluminescence transition at 510nm.Item Inverkan av kväve, vismut och temperatur på vakans- och defektdistributionen i GaSb(Aalto University, 2013) Segercrantz, Natalie; Slotte, Jonatan; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science; Tuomisto, Filip, Prof.Item On the Evolution of Strain and Electrical Properties in As-Grown and Annealed Si: P Epitaxial Films for Source-Drain Stressor Applications(2018) Dhayalan, Sathish Kumar; Kujala, Jiri; Slotte, Jonatan; Pourtois, Geoffrey; Simoen, Eddy; Rosseel, Erik; Hikavyy, Andriy; Shimura, Yosuke; Loo, Roger; Vandervorst, Wilfried; Department of Applied Physics; Antimatter and Nuclear Engineering; IMEC Vzw; University of Antwerp; Ghent UniversityHeavily P doped Si:P epitaxial layers have gained interest in recent times as a promising source-drain stressor material for n type FinFETs (Fin Field Effect Transistors). They are touted to provide excellent conductivity as well as tensile strain. Although the as-grown layers do provide tensile strain, their conductivity exhibits an unfavorable behavior. It reduces with increasing P concentration (P > 1E21 at/cm(3)), accompanied by a saturation in the active carrier concentration. Subjecting the layers to laser annealing increases the conductivity and activates a fraction of P atoms. However, there is also a concurrent reduction in tensile strain (Item On the manifestation of phosphorus-vacancy complexes in epitaxial Si:P films(2016-02-22) Dhayalan, Sathish Kumar; Kujala, Jiri; Slotte, Jonatan; Pourtois, Geoffrey; Simoen, Eddy; Rosseel, Erik; Hikavyy, Andriy; Shimura, Yosuke; Iacovo, Serena; Stesmans, Andre; Loo, Roger; Vandervorst, Wilfried; IMEC Vzw; Department of Applied Physics; University of Antwerp; KU LeuvenIn situ doped epitaxial Si:P films with P concentrations >1 × 1021 at./cm3 are suitable for source-drain stressors of n-FinFETs. These films combine the advantages of high conductivity derived from the high P doping with the creation of tensile strain in the Si channel. It has been suggested that the tensile strain developed in the Si:P films is due to the presence of local Si3P4 clusters, which however do not contribute to the electrical conductivity. During laser annealing, the Si3P4 clusters are expected to disperse resulting in an increased conductivity while the strain reduces slightly. However, the existence of Si3P4 is not proven. Based on first-principles simulations, we demonstrate that the formation of vacancy centered Si3P4 clusters, in the form of four P atoms bonded to a Si vacancy, is thermodynamically favorable at such high P concentrations. We suggest that during post epi-growth annealing, a fraction of the P atoms from these clusters are activated, while the remaining part goes into interstitial sites, thereby reducing strain. We corroborate our conjecture experimentally using positron annihilation spectroscopy, electron spin resonance, and Rutherford backscattering ion channeling studies.Item Open volume defects in ultra-thin TiO2 layers embedded in VMCO-like samples studied with positron annihilation spectroscopy(American Institute of Physics, 2022-06-24) Khanam, Afrina; Slotte, Jonatan; Tuomisto, Filip; Subhechha, Subhali; Popovici, Mihaela; Kar, Gouri Sankar; Department of Applied Physics; Antimatter and Nuclear Engineering; University of Helsinki; IMEC VzwPositron annihilation signals from VMCO-like samples grown by atomic layer deposition at different temperatures are utilized for the characterization of differences in open volume defects in TiN/TiO2/a-Si heterostructures. Doppler and coincidence Doppler mode of positron annihilation spectroscopy combined with a monoenergetic positron beam were used for this study. Differences observed in the Doppler parameters indicate differences in the positron trapping states of the TiO2 epilayers grown at different temperatures. Furthermore, the coincidence-Doppler results show that these differences cannot be due to intermixing of the TiO2 and a-Si layers and formation of thin SiO2 layers at the interface during the growth process. The results indicate that the amount of open volume defects in the TiO2 layer of the VMCO-structure seems to increase with an increase in the growth temperature.Item Source/Drain Materials for Ge nMOS Devices: Phosphorus Activation in Epitaxial Si, Ge, Ge1-xSnx and SiyGe1-x-ySnx(ELECTROCHEMICAL SOC INC, 2020-05-07) Vohra, Anurag; Makkonen, Ilja; Pourtois, Geoffrey; Slotte, Jonatan; Porret, Clement; Rosseel, Erik; Khanam, Afrina; Tirrito, Matteo; Douhard, Bastien; Loo, Roger; Vandervorst, Wilfried; Department of Applied Physics; Antimatter and Nuclear Engineering; University of Antwerp; IMEC Vzw; Polytechnic University of Turin; KU Leuven; University of HelsinkiThis paper benchmarks various epitaxial growth schemes based on n-type group-IV materials as viable source/drain candidates for Ge nMOS devices. Si:P grown at low temperature on Ge, gives an active carrier concentration as high as 3.5 × 1020 cm−3 and a contact resistivity down to 7.5 × 10−9 Ω.cm2. However, Si:P growth is highly defective due to large lattice mismatch between Si and Ge. Within the material stacks assessed, one option for Ge nMOS source/drain stressors would be to stack Si:P, deposited at contact level, on top of a selectively grown n-Si y Ge1−x−y Sn x at source/drain level, in line with the concept of Si passivation of n-Ge surfaces to achieve low contact resistivities as reported in literature (Martens et al. 2011 Appl. Phys. Lett., 98, 013 504). The saturation in active carrier concentration with increasing P (or As)-doping is the major bottleneck in achieving low contact resistivities for as-grown Ge or Si y Ge1−x−y Sn x . We focus on understanding various dopant deactivation mechanisms in P-doped Ge and Ge1−x Sn x alloys. First principles simulation results suggest that P deactivation in Ge and Ge1−x Sn x can be explained both by P-clustering and donor-vacancy complexes. Positron annihilation spectroscopy analysis, suggests that dopant deactivation in P-doped Ge and Ge1−x Sn x is primarily due to the formation of P n -V and Sn m P n -V clusters.Item Termisten vakanssien tutkiminen germaniumissa ja piissä(2010) Laine, Hannu; Slotte, Jonatan; Informaatio- ja luonnontieteiden tiedekunta; Puska, MarttiItem Vacancy-type defects in strained Si1-xGex layers studied by positron annihilation spectroscopy(2003) Sihto, Sanna-Liisa; Slotte, Jonatan; Teknillisen fysiikan ja matematiikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Saarinen, Kimmo