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Content: Preface Selected publications Statistics (Publications and patents, Concluded scientific degrees; Appointments and honors; Invited conference contributions, colloquia, lectures and talks; Conferences, workshops, colloquia and seminars; Exchange of researchers; Projects) Doctoral training programme Experimental equipment User facilities and services Organization chart and personnel

After the successful evaluation in 2015 we started research and further development of our largescale facilities, in particular the Ion Beam Center (IBC), in the framework of Helmholtz’s Programmeoriented Funding scheme (POF) which coordinates scientific cooperation on a national and international scale. Most of our activities are assigned to the Helmholtz program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a minor part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”. A few highlights which have been published in 2015 are reprinted in this annual report in order to show the variety of the research being performed at the Institute, ranging from self-organized pattern formation during ion erosion or DNA origami patterning, over ferromagnetism in SiC and TiO2 to plasmonics and THz-spectroscopy of III-V semiconductors. A technological highlight published recently is the demonstration of nanometer scale elemental analysis in a Helium ion microscope, making use of a time-of-flight detector that has been developed at the IBC. In addition to these inhouse research highlights, also users of the IBC, in particular of the accelerator mass spectrometry (AMS), succeeded in publishing their research on geomorphology in Nepal in the high-impact journal Science (W. Schwanghart et al., Science 351, 147 (2015)), which demonstrates impressively the added value of transdisciplinary research at the IBC. In order to further develop the IBC, we have started in 2015 the design and construction of our new low energy ion nanoengineering platform which was highly recommended by the POF evaluators. It will consist of two-dimensional materials synthesis and modification, high-resolution ion beam analysis and high-resolution electron beam analysis and will come into full operation in 2019.

Independent of the type of doping, it is challenging to achieve in semiconductors an effective carrier concentration much above 10^20 /cm3. On the other hand, the successful realization of defect free n-type and p-type ultra-doped Ge layers will enable a range of devices from sensors to quantum computers. In the case of conventional doping techniques (using equilibrium processing) the maximum carrier concentration is limited by the out-diffusion of dopants, a relatively low solid solubility limit, clustering and self-compensation processes. To overcome such limitations we have utilised strong nonequilibrium process consisting of an ion beam implantation to introduce dopants into Ge and rear-side millisecond range flash lamp annealing (FLA) for recrystallization of implanted layer and dopant activation. In contrast to conventional annealing procedures, rear-side FLA leads to full recrystallization of Ge and dopant activation independent of the pre-treatment. The maximum carrier concentration is well above 10^20 /cm3 for n-type and above 10^21 /cm3 for p-type dopants. The so-fabricated n-type Ge can be used in the field of mid-infrared plasmonics which has not been accessible by group-IV semiconductors. Single crystalline n-type Ge with carrier concentrations as high as 2.2×10^20 /cm3 displays a room-temperature plasma frequency above 1850 /cm1 (?=5.4 ?m), which is the highest value ever reported for n-type Ge. In the case of Ga implanted Ge the maximum effective carrier concentration measured at 3K is 1.1×10^21 /cm3 which is two times higher than the solid solubility limit of Ga in Ge. Our p-type Ge is defect and cluster free and shows the superconductivity at Tc = 0.95 K. These results base on the successful combination of ion beam implantation followed by the novel approach consisting of millisecond range rear-FLA. This work has been partially supported by the EU 7th Framework Programme "EAgLE" (REGPOT-CT-2013-316014).

This past year 2014 was the year when we finally completely arrived as a “full member” in the Helmholtz Association. This is related to the successfully passed research evaluation in the framework of the Program Oriented Funding (POF), which will give us a stable and predictable funding for the next five years (2015 – 2019). This is particularly true for our large-scale user facilities, like the Ion Beam Center (IBC) and the electron accelerator ELBE with the free-electron laser. Most of our activities are assigned to the program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a small part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”. Our research and facilities were well appreciated by the evaluation committee, who made the following judgement about the Ion Beam Center: “The Ion Beam Centre (IBC) of HZDR is an internationally leading ion-beam facility (with ion energies ranging from several eV to several tens of MeV). At both the national and international level it is one of the key players and is unique in its kind. The synergy between forefront research and user service has been leading to a very good publication output for both in-house research and user research. … The very broad range of beam energies, the versatility of techniques and applications – both for ion beam modification of materials and for ion-beam analysis – makes the IBC unique in its kind. … The strength of IBC is that its activities are based on a combination of forefront research and user service, which mutually interact in synergy and strengthen one another. In turn, this synergy has been leading to a very good publication output for both in-house research and user research.” In order to make our Annual Report a bit more compact, we have decided to include only four full journal papers this year. This was also triggered by the fact that our publication activities have turned out be become more diverse, in more diverse journals than in the past, and often through longer papers, which would be too long to reprint them here. However, apart from the constantly quantitatively high publication output, we succeeded to publish in excellent journals such as Nature Physics, Nano Letters and Physical Review Letters, in fields as diverse as ion beam physics, magnetism and terahertz spectroscopy. Two of our scientists, Dr. Artur Erbe and Dr. Alexej Pashkin obtained their Habilitation in 2014, both at University of Konstanz. For the first time, we are hosting an Emmy Noether Young Investigator Group funded by the Deutsche Forschungsgemeinschaft (DFG); the group works on the hot topic of magnonics and is headed by Dr. Helmut Schultheiß. Finally we would like to cordially thank all partners, friends, and organizations who supported our progress in 2014. Special thanks are due to the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Minister of Education and Research of the Federal Government of Germany. Numerous partners from universities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank again all IIM staff for their efforts and excellent contributions in 2014.

The year 2013 was the third year of HZDR as a member of the Helmholtz Association (HGF), and we have made progress of integrating ourselves into this research environment of national Research centers. In particular, we were preparing for the evaluation in the framework of the so-called program oriented funding (POF), which will hopefully provide us with a stable funding for the next five years (2015 – 2019). In particular, last fall we have submitted a large proposal in collaboration with several other research centers. The actual evaluation will take place this spring. Most of our activities are assigned to the program “From Matter to Materials and Life” (within the research area “Matter”). A large fraction of this program is related to the operation of large-scale research infrastructures (or user facilities), one of which is our Ion Beam Center (IBC). The second large part of our research is labelled “in-house research”, reflecting the work driven through our researchers without external users, but still mostly utilizing our large-scale facilities such as the IBC, and, to a lesser extent, the free-electron laser. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a small part of our activities in the program “Nuclear Waste Management and Safety” (within the research area “Energy”).

Ga-rich (~ 10 at.%) Si and Ge films were fabricated by high-fluence Ga+ ion implantation through a SiO2 capping layer. The structure and the electrical transport properties of these films have been studied after flash-lamp [1-3] and rapid thermal annealing [4, 5]. Amorphous, Ga-rich nanoprecipitates are embedded in a heavily p-type doped semiconductor matrix [3, 4]. These nanoprecipitates become superconducting below critical temperatures up to 7 K. They can interact due to the proximity effect in the degenerately doped semiconductor matrix and form a random network of Josephson junctions. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. In particular, Ga-rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance [6, 7] . The possibility to prepare and modify Ga-rich Si and Ge films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices. [1] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, et al., Phys. Rev. Lett.,2009, 102, 217003. [2] R. Skrotzki, T. Herrmannsdörfer, V. Heera, J. Fiedler, et. al., Low Temp. Phys., 2011, 37, 1098. [3] V. Heera, J. Fiedler, M. Naumann, R. Skrotzki, et al., Supercond. Sci. Technol., 2014, 27, 055025. [4] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2011, 83, 214504. [5] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2012, 85, 134530. [6] V. Heera, J. Fiedler, M. Voelskow, A. Mücklich, et al., Appl. Phys. Lett., 2012, 100, 262602 [7] V. Heera, J. Fiedler, R. Hübner, B. Schmidt, et al., New. J. Phys., 2013, 15, 083022

Ge films with a mean Ga content of about 8 at.% and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change of the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters up to 10,000 atoms. Since no percolating Ga cluster exists, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect.

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In 2012 the HZDR, and in consequence also the Institute of Ion Beam Physics and Materials Research (IIM) including its Ion Beam Center (IBC), has undergone a scientific evaluation. The evaluation committee composed of the Scientific Advisory Board and numerous external experts in our field of research concluded that “the overall quality of the scientific work is excellent”, that “there are an impressive number of young scientists working enthusiastically on a variety of high-level projects” and that “the choice of these projects represents a clear underlying strategy and vision”. We feel honored and are proud that the external view on our scientific achievements is that extraordinary. In view of this outstanding result we would like to express our gratitude to all our staff members for their commitment and efforts! In the past year, we continued our integration into the Helmholtz Association of German Research Centers (HGF) with our Institute mostly active in the research area “Matter”, but also involved in a number of activities in the research area “Energy”. In this respect, many consultations were held with the Helmholtz centers contributing to common research areas to precisely define the role we will play in the newly established HGF program “From Matter to Materials and Life” (see schematic below). Our IBC has been recognized as a large-scale user facility for ion beam analysis and modification of materials, i.e., specializing on materials science. In particular, the IBC plays a prominent role in the recently approved Helmholtz Energy Materials Characterization Platform (HEMCP), which mainly concentrates on the development of dedicated analytical tools for the characterization of materials required for future energy technologies. The successes achieved by the IBC allows us to invest 7200 k€ to further improve and strengthen the ion beam capabilities at the Institute. In addition to this infrastructure-related grant, we were also successful in our funding application for the establishment of the International Helmholtz Research School for Nanoelectronic Networks (IHRS NANONET), aiming at promoting the next generation of leading scientists in the field of nanoelectronics. The IHRS NANONET is coordinated by our Institute and offers a well-structured PhD program to outstanding students of all nationalities with emphasis on interdisciplinary research and comprehensive training in technical and professional skills.

Si films sputter deposited on SiO2 substrates are enriched with Ga by ion implantation through a capping SiO2 layer. The morphology and the electrical transport properties of these films are investigated after rapid thermal annealing. Amorphous, Ga rich nanograins are embedded in a nanocrystalline Si matrix. The nanograins are metallic in the normal state and superconducting below 7 K. They form a random network of junctions to heavily doped Si crystallites. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. Ga rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current controlled sheet resistance. The possibility to fabricate and tailor films of Ga rich Si with microelectronics compatible technology make it a promising material for the integration of superconducting circuits into Si devices.

Superconducting Ga-rich layers in Ge are fabricated by Ga implantation through a thin SiO2 cover layer. After annealing in a certain temperature window, Ga accumulation at the SiO2/Ge interface is observed. However, no Ga containing crystalline phases are identified. Thus it is suggested that the volatile Ga is stabilized in an amorphous mixture of all elements available at the interface. Electrical transport measurements reveal p-type metallic conductivity and superconducting transition. The superconducting properties of the samples with high Ga concentration at the interface change dramatically with etching the amorphous surface layer. A critical temperature of 6 K is measured before, whereas after etching it drops below 1 K. Therefore, one can conclude that the superconducting transport is based on two different layers: a Ga-rich amorphous phase at the interface and a heavily Ga-doped Ge layer. Finally, the comparison of the transport properties of Ga-rich Ge with those of Si demonstrates distinct differences between the interface layers and even the deeper lying doped regions.

We report on two unconventional routes of embedding superconducting nanolayers in a semiconducting environment. Ion implantation and subsequent annealing have been used for preparation of superconducting thin-films of Ga-doped germanium (Ge:Ga) [1] as well as 10 nm thin amorphous Ga-rich layers in silicon (Si:Ga) [2]. Structural investigations by means of XTEM, EDX, RBS/C, and SIMS have been performed in addition to low-temperature electrical transport and magnetization measurements. Regarding Ge:Ga, we unravel the evolution of Tc with charge-charrier concentration while for Si:Ga recently implemented microstructuring renders critical-current densities or more than 50 kA/cm2. Combined with a superconducting onset at around 10 K, this calls for onchip application in novel heterostructured devices.

Die Erfindung beschreibt die Herstellung integrierter supraleitender Strukturen in Schaltungen und Schaltungselementen auf der Basis von Silizium- bzw. Germanium-Wafern durch Implementieren von Ausscheidungen, neuen chemischen Verbindungen oder einer Dotierung via Ionenimplantation und anschließender Kurzzeitausheilung. Vorteil dieser Strukturen ist die kostengünstige Produktion, und der höheren Leistungsdichte dieser Schaltungen bezüglich Transistorschaltungen. Diese Strukturen ermöglichen die Steuerung quantenmechanischer Interferenzerscheinungen mit Hilfe eines äußeren Magnetfeldes oder auf dem Chip erzeugten Magnetfeldes. Eine weitere Einsatzmöglichkeit bieten Logikschaltungen für das Quantum Computing.

The first year of membership of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in the Helmholtz Association of German Research Centers (HGF) was a year of many changes also for the Institute of Ion Beam Physics and Materials Research (IIM). The transition period, however, is not yet over, since the full integration of the Center into the HGF will only be completed in the next period of the so-called program-oriented funding (POF). This funding scheme addresses the six core research fields identified by the Helmholtz Association (Energy; Earth and Environment; Health; Key Technologies; Structure of Matter; Aeronautics, Space and Transport) to deal with the grand challenges faced by society, science and industry. Since the Institute has strong contributions to both core fields “Key Technologies” and “Structure of Matter”, intense discussions were held amongst the leading scientists of the Institute, across the Institutes of the HZDR, and finally with leading scientists of other Helmholtz centers, to determine the most appropriate classification of the Institute’s research. At the end we decided to establish ourselves in Structure of Matter, the core field in which most of the large-scale photon, neutron and ion facilities in Germany are located. As a consequence, the Ion Beam Center (IBC) of the Institute submitted an application to become a HGF recognized large-scale facility, providing more than 50% of its available beam time to external users. This application perfectly reflects the development of the IBC over more than a decade as a European Union funded infrastructure in the framework of the projects “Center for Application of Ion Beams in Materials Research (AIM)” (1998-2000, 2000-2003, 2006-2010) and subsequently as the coordinator of the integrated infrastructure initiative (I3) “Support of Public and Industrial Research using Ion Beam Technology (SPIRIT)” (2009-2013). Another part of the Institute’s activities is dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. This facility is also open to external users and funded by the European Union.

Superconductivity in elemental group-IV semiconductors is of great interest because of both, the high potential for new microelectronic applications and its underlying physics. To observe superconductivity at ambient pressure conditions high doping levels are needed. Sufficient doping concentrations of few at.% were achieved first for boron doped diamond [1]. Suprisingly also silicon, the basic material of todays microelectronic indurstry becomes superconducting below 0.6 K when heavily doped with boron [2]. In our previous work we used ion implantation and short-term annealing to fabricate superconducting Ga doped Ge layers with critical temperatures below 1 K [3]. The solid solubility is exceeded by far and therefore the presence of Ga clusters has to be excluded [4]. However the question arises, how superconducting precipitates influence the low- temperature transport properties. We demonstrate the possibility of embedding extrinsic superconducting nanolayers in commercial microelectronic Si wafers. Ga implantation (4x1016cm-2) through a 30 nm SiO2 cover layer is used because Ga itself is a superconducting element. Sturctural investigations by means of RBS/C and TEM reveal the stabilization of a Ga-rich layer at the SiO2/Si interfae after rapid thermal annealing (RTA). At defined RTA temperatures of 600 – 700°C this interface layer becomes superconducting [5,6]. Amorphous Ga has a critical temperature of 7 K which is comparable to the value of our Ga-rich interface layers. High critical magnetic fields up to 14 T and critical current densities as high as 50 kA/cm2 make the Si:Ga layers interesting for applications. These results in combination with investigations on similar prepared Ga-rich layers at SiO2/Ge interfaces imply that superconductivity driven by Ga clusters occurs at temperatures of 6 – 7K [7]. If in Ge the onset of superconductivity is below 1 K, it can clearly be attributed to a doping effect. Financial support by DFG (HE 2604/7-1) is gratefully acknowledged. [1] E. A. Ekimov et al., Nature 2004;428:542. [2] E. Bustarret et al., Nature 2006;444:465. [3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 2009;102:217003. [4] V. Heera et al., J. Appl. Phys. 2010;107:053508. [5] R. Skrotzki et al., Appl. Phys. Lett. 2010;97:192505. [6] J. Fiedler et al., Phys. Rev. B 2011;83:214504. [7] J. Fiedler et al., Phys. Rev. B 2012;85:134530.

Superconductivity is a fascinating ground state of matter and has been discovered one century ago. A new debate about the fundamental physical background and technological potential of superconducting group-IV semiconductors occurred, since superconductivity at ambient pressure conditions was shown for boron doped diamond [1] and silicon [2]. These unusual superconductors open the way towards new microelectronic devices and applications. In our previous work, we used Ga-ion implantation and subsequent short-time annealing for creating highly Ga doped layers in Ge. [3] These layers show an intrinsic superconducting transition at temperatures below 1 K because of the high doping level. [4] In a next step we could show the feasibility to stabilize Ga-rich layers at SiO2/Si [5,6] and SiO2/Ge [7] interfaces by using a 30 nm SiO2 cover layer during implantation and annealing. The presented structural investigations by means of Rutherford Backscattering Spectrometry (RBS) and cross-sectional Transmission Electron Microscopy (XTEM) reveal the presence of a 10 nm thin, superconducting layer at the interfaces containing Ga-rich precipitates. In both cases the critical temperature increases to 7 K which is comparable to amorphous Ga and therefore enables the detailed investigation of the influence of superconducting precipitates on the superconducting properties of doped semiconductor layers. However, the previous investigations were done on 1 x 1 cm2 size samples. The possibility of fabricating superconducting microstructures in Si with standard microelectronic lithography will be shown. Theses microstructures still undergo a superconducting transition below 7 K. High critical magnetic fields in the range of 10 T and high critical current densities of 50 kA/cm2 were achieved. For applications in superconducting microelectronics a Josephson-Junction has to be implemented. [8] We plan to use a Focused Ion Beam (FIB) for this task. Details about the sample processing, layer microstructure and processing of superconducting microstructures will be presented. [1] E. A. Ekimov et al., Nature (London) 428 (2004) 542. [2] E. Bustarret et al., Nature 444 (2006) 465. [3] V. Heera et al., J. Appl. Phys. 107 (2010) 053508. [4] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003. [5] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505. [6] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504. [7] J. Fiedler et al., Phys. Rev. B 85 (2012) 134530. [8] J. Q. You et al., Nature 474 (2011) 589.

Beginning in 2004, the interest in superconductivity of elemental group-IV semiconductors has been renewed because Ekimov et al. [1] showed that boron doped diamond could become superconducting at ambient pressure conditions. Besides fundamental physical background of driving a semiconductor into a superconducting state, the high potential for applications in new microelectronic devices is in the main focus. High doping levels are needed to observe superconductivity at ambient pressure conditions in elemental group-IV semiconductors. Gas immersion laser doping is used to fabricate superconducting boron doped silicon [2]. The possibility to use Ga-ion implantation and short-time annealing for creating superconducting Ga-doped Ge layers was shown in our previous work [3, 4]. These highly doped Ge-layers show an onset of superconductivity below 1 K. All doping techniques mentioned above exceed the equilibrium solid solubility limit by far and the question arises, whether the observed superconductivity is a doping effect or related to dopant clusters [5]. Especially if the doping element itself is a superconductor, like Ga in Ge, it was not clear how superconducting precipitates influence the low-temperature transport properties. To investigate these effects, we stabilized superconducting Ga-rich layers at SiO2/Si interfaces [6, 7]. Again, we have used ion implantation through a 30 nm thick SiO2 cover layer and rapid thermal annealing. The critical temperature of 7 K is comparable to the values obtained for amorphous Ga. Furthermore, high critical magnetic fields of 14 T and critical current densities of 50 kA/cm2 were achieved. With the results of the investigations discussed above, we could go one step further and fabricate similar Ga-rich layers at SiO2/Ge interfaces. Now it is possible to investigate selectively the influence of superconducting Ga-rich areas on the normal- and superconducting properties of Ga-doped Ge. It will be shown that the critical temperature changes dramatically while the critical magnetic field stays rather constant. The results of detailed microstructural investigations by means of XTEM and time-of-flight SIMS will be correlated with electrical properties. Finally, the presented results indicate that superconductivity with critical temperatures around 1 K can clearly be attributed to a doping effect. [1] E. A. Ekimov et al., Nature (London) 428 (2004) 542. [2] E. Bustarret et al., Nature 444 (2006) 465. [3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003. [4] V. Heera et al., J. Appl. Phys. 107 (2010) 053508. [5] N. Dubrovinskaia et al., PNAS 105 (2008) 11619. [6] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505. [7] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504.

TEM investigation contributing to the comprehension of superconductivity in Ga-doped Si

Ga-rich layers in Si were fabricated by 80 keV Ga implantation through a 30 nm SiO2 cover layer and subsequent rapid thermal annealing for 60 s in a temperature range between 500°C and 1000°C. Fluences of 2x1016cm-2 and 4x1016cm-2, leading to Ga peak concentrations of 8 at.% and 16 at.%, are chosen. Residual damage in the implanted layers and the Ga distribution were investigated by Rutherford-backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy and X-ray photoelectron spectroscopy. Temperature dependent Hall-effect measurements were carried out in order to determine the electrical properties of the implanted layers. It is shown that annealing at temperatures up to 800°C leads to the formation of poly-crystalline layers containing random distributed amorphous clusters. At the Si/SiO2 interface a dense and narrow band of Ga-rich clusters is observed. For 4x1016cm-2 the amount of mobile Ga is higher than for 2x1016cm-2 and an increase of the cluster density at the Si/SiO2 interface was found. Due to the higher cluster density for 4x1016cm-2 this interface layer can become superconducting below 7 K with critical fields exceeding 9 T at optimized annealing conditions. Critical currents are above 1 kA/cm2 and therefore this seems to be a possible material system for future microelectronic applications. After annealing at 900°C and above, the implanted layers are single crystalline and no amorphous precipitates were found.

The feasibility of embedding extrinsic superconducting nanolayers in commercial (100) silicon due to Ga precipitation is presented. To be far beyond the solid solubility limit of 0.1 at.% a high Ga fluence of 4x1016cm-2 is introduced in silicon by the ion-implantation technique. This leads to 100 nm thick amorphous silicon layers with a Ga peak concentration of 16 at.%. Subsequent recrystallization and Ga precipitation is initiated via rapid thermal annealing (RTA) for 60 seconds at temperatures of 500 – 800°C. A 30 nm sputter deposited SiO2 cover layer is used to protect the silicon surface during implantation and prevent Ga out-diffusion during annealing. It was shown that optimized annealing conditions (600 – 700°C) lead to superconducting layers with critical temperatures of 7 K and in plane critical fields up to 14 T [1]. Details of the layer microstructure investigations using of RBS/C and TEM as well as depth dependent XPS will be presented. The presented structural investigations reveal poly-crystalline silicon layers and show a strong Ga enrichment at the Si/SiO2 interface. Even if no crystalline Ga clusters were detected it is shown that the superconductivity arises due to a high density of amorphous Ga-rich precipitates at the Si/SiO2 interface. Since all involved processing steps are fully compatible with standard microelectronic technology and high criti-cal current densities of more than 2 kA/cm2 are reached, the proposed material system may implicate a high potential for future microelectronic applications. [1] Skrotzki R. et al., Appl. Phys. Lett. 97 (2010) 192505

Recently it has been shown that heavily p-doped group-IV semiconductors such as diamond, silicon and germanium can become superconducting at low temperatures. Here, we present a study of Ga-implanted Si that becomes superconducting due to precipitation after annealing. Ion implantation allows introducing a high Ga dose (4E16cm-2) in Si that leads to peak concentrations far beyond the solid solubility limit. Rapid thermal annealing (RTA) causes redistribution of the Ga and re-crystallization of the amorphous implanted Si layer. After annealing at temperatures up to 850°C the implanted layers are polycrystalline and contain Ga-rich precipitates. Structural investigations by means of RBS/C measurements and TEM demonstrate a high density of precipitates at the interface of a protective SiO2 layer and the silicon substrate. At optimized annealing conditions (600-700°C) such samples become superconducting with critical temperatures up to 7 K [1]. [1] Skrotzki R. et al. , Appl. Phys. Lett. 97 (2010) 192505

The Institute of Ion Beam Physics and Materials Research (IIM) is one of the six institutes of what was called Forschungszentrum Dresden-Rossendorf (FZD) until the end of 2010, but since this year 2011 is called “Helmholtz-Zentrum Dresden-Rossendorf (HZDR)”. This change reflects a significant transition for us: it means that the research center is now member of the Helmholtz Association of German Research Centers (HGF), i.e., a real government research laboratory, with the mission to perform research to solve fundamental societal problems. Often to date those are called the “Grand Challenges” and comprise issues such as energy supply and resources, health in relation to aging population, future mobility, or the information society. This Annual Report already bears the new corporate design, adequate for the time of its issueing, but reports results from the year 2010, when we were still member of the Leibniz Association (WGL). Our research is still mainly in the fields of semiconductor physics and materials science using ion beams. The institute operates a national and international Ion Beam Center, which, in addition to its own scientific activities, makes available fast ion technologies to universities, other research institutes, and industry. Parts of its activities are also dedicated to exploit the infrared/THz freeelectron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. For both facilities the institute holds EU grants for funding access of external users.

We present two unconventional routes of embedding superconducting nanolayers in a semiconducting environment. On the one hand, ion implantation and subsequent annealing have been used to prepare intrinsic superconducting thin-films of Ga-doped germanium (Ge:Ga) with Tc of 0.5 to 1.2 K. On the other hand, the same technique has been applied to fabricate thin amorphous Ga-rich layers in silicon (Si:Ga) revealing a Tc of about 7 K. Extended structural investigations by means of XTEM, EDX, RBS/C, and SIMS have been performed in addition to low-temperature electrical transport and magnetization measurements. A narrow window of preparation parameters turns out to be necessary to obtain best sample properties in a reproducible way. While Ge:Ga films scale 60 - 100 nm and reveal a small critical current density Jc ≈ 3 A/cm2, Si:Ga layers exhibit Jc > 1 kA/cm2 and a thickness of 15 nm. Relative high and anisotropic critical fields have been found for both nanostructures proving their quasi-two-dimensionality. The implementation of prospective microstructuring may offer an on-chip combination of super- and semiconducting circuits that could be integrated in novel heterostructured devices.

We demonstrate the feasibility of embedding superconducting Ga nanolayers in commercial (100) oriented silicon wafers and discuss the possibility of potential device applications [1]. Ion implantation and rapid thermal annealing, known as versatile tools of microelectronic technology, have been used for inserting and distributing a gallium dose of up to 4 × 1016 cm2. As proven by structural analysis, a 10 nm thin layer of amorphous Ga-rich precipitates forms during annealing at 600 - 700°C. These structures exhibit a superconducting transition at 7 K. Extended resistivity and magnetization measurements reveal in-plane critical fields around 14 T and critical current densities exceeding 2 kA/cm2. In summary, we proceed with an optimistic outlook concerning the implementation of prospective microstructuring. After all, this would be the next step towards the development of novel semiconductor-based superconducting devices.

Germanium is currently considered as a potential replacement for silicon devices [1]. The formation of heavily doped, shallow junctions in Ge by ion im-plantation and appropriate annealing techniques is under investigation [2, 3]. In contrast to Si the Ge surface is severely affected by irradiation damage. Im-plantation into the uncovered Ge surface leads to sur-face roughening and even porous layers [3]. Therefore, the Ge surface must be protected by a thin cover layer, which is commonly a sputtered SiO2-layer between 10 and 30 nm. This cover layer remains on the Ge sample also during annealing. For light dopants like B or P this oxide layer remains stable and smooth. However, with increasing ion mass and fluence surface erosion and oxide degradation can occur. A relatively heavy ion of interest is Ga [3]. It is a shallow acceptor with a high solid solubility in Ge. We studied the effect of Ga im-plantation through a SiO2 cover layer.

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The discovery of superconductivity in heavily boron-doped diamond [1] has demonstrated that group-IV semiconductors can become superconducting upon carrier doping even at ambient conditions. Meanwhile superconductivity has been found in further heavily doped group-IV semiconductors such as Si and SiC [2]. Compared to these semiconductors, Ge seems to be less promising for realizing superconductivity as was based upon estimates of the electron-phonon coupling strength [3]. The challenge is to achieve extremely high hole concentrations which are commonly limited by the equilibrium solid solubility of the acceptor. Nevertheless, we succeeded in making Ge superconducting as recently reported [4]. A nonequilibrium doping process consisting of 100 keV Ga+-ion implantation with a fluence of 21016cm-2 and subsequent 3 ms flash-lamp annealing (FLA) enabled hole concentrations as high as 1.41021 cm-2. The superconducting state was observed in a thin (~60 nm) Ge layer with a maximum Ga content of about 8 at.% at critical temperatures below 0.5 K. From the measured critical parameters it follows that Ga-doped Ge is a type-II superconductor with a large Ginzburg-Landau parameter (>103). The structure as well as the superconducting properties of the Ga-doped Ge layers depend sensitively on the preparation conditions as shown in Fig. 1. In search for higher transition temperatures, implantation and annealing conditions were varied in a more comprehensive study. Critical temperatures above 1 K were obtained for samples either implanted with 41016 cm-2 and flash-lamp annealed at 52 Jcm-2 or implanted with 21016 cm-2 and subjected to rapid thermal annealing (RTA) at 910°C for 60 s (Fig. 2). Critical magnetic fields perpendicular and parallel to the Ge:Ga plane up to about 0.3 and 1 T, respectively, were observed. Thus superconductivity in thin Ge:Ge layers is a robust effect and could be utilized in superconducting quantum devices. [1] E. A. Ekimov, V. A. Sidorov, E. D. Bauer, et al., Nature 428, 542 (2004) [2] K. Iakoubovskii, Physica C 469, 675 (2009) [3] L. Boeri, J. Kortus, O. K. Anderson, J. Phys. Chem. Solids 67, 552 (2006) [4] T. Herrmannsdörfer, V. Heera, O. Ignatchik, et al., Phys. Rev. Lett. 102, 217003 (2009)

In the past the lack of stable native germanium oxide for surface passivation and gate dielectrics as well as the inability to epitaxially grow sufficiently thick defect-free germanium layers on silicon hindered the integration of germanium into the mainstream Si-based technology. Recent developments, such as high-k dielectrics and germanium-on-insulator substrates have made germanium a promising candidate for future high mobility devices. Therefore electrical doping of germanium by ion implantation and subsequent annealing has drawn a renewed interest. Investigations on the formation of ultra shallow junctions by ion beam processing have shown that p+-doping using B yields junctions that meet the requirements for the 22 nm technology node, whereas the formation of n+-junctions by P or As is complicated by the high diffusivity and the low solubility of the dopants. Recently, the concentration-dependent diffusion of n-dopants like P, As and Sb has been explored, and it has been found that doubly negatively charged vacancies are the mobile species responsible for the migration of the dopant atoms. The application of conventional rapid thermal annealing (RTA) with durations of some seconds and temperatures above about 500 °C leads to the activation of the n-dopants but their fast concentration-dependent diffusion can generally not be prevented. On the other hand it has been shown that both the diffusion and the activation of the dopants does not depend significantly on the implantation damage, i.e. using the defect engineering schemes known from Si technology seems not to be promising. Therefore, in order to control junction depth and dopant activation ultra-short annealing by flash lamps or lasers are currently under investigation. The present work deals with the application of millisecond flash lamp annealing (FLA) to samples containing an implanted surface layer of about 100 nm thickness. P or As ions were implanted at an energy of 30 or 90 keV, respectively, and a fluence of 3x1015 cm-2. The investigations are focused on solid phase epitaxial recrystallization, dopant redistribution and dopant activation. The dependence of these effects on the heat transfer to the sample during FLA as well as on pre-amorphization and pre-annealing treatment is discussed. The results are compared to typical data achievable by RTA. Different characterization methods were employed. Channeling Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy (XTEM) were used to monitor the recrystallization of the amorphous layers formed during implantation. The depth distributions of P and As were measured by secondary ion mass spectrometry. In order to determine the sheet resistance variable probe spacing and micro four point probe measurements were utilized. Selected samples were studied by XTEM to search for precipitates and end-of-range defects. While in RTA the concentration dependent dopant diffusion hinders the formation of ultra-shallow n+ layers, FLA does not cause any diffusion. The maximum activation obtained by FLA is about 6x1019 and 2x1019 cm-3 for P and As, respectively. This is about 3-4 times higher than under typical RTA conditions. However, the activation and the sheet resistance achieved by FLA do not yet fulfill the ITRS requirements for the 22 nm technology node. Possible mechanisms responsible for dopant deactivation are discussed.

We report recent discoveries of superconductivity in Ga-doped germanium fabricated by ion implantation and subsequent flash-lamp or oven annealing. Tuning the preparation parameters allows for varying both charge-carrier and Ga concentration in the resulting roughly 100 nm thin nano- or single-crystalline layers. Transport measurements on systematically prepared samples reveal that besides a needed charge-carrier concentration of more than 0.4 atom%, superconductivity occurs to be sensitive on the implanted Ga content which may also be attributed to a change in the phonon properties. Onset transition temperatures up to 1.4 K have been found for almost 10 atom% Ga. Further, we observe in-plane critical fields exceeding 1 T and being close to the Pauli-Clogston limit. An exceptionally low Cooper-pair density of around 1015 cm−3 turns out the extreme type-II character of superconductivity. Finally, our work adds to our previous report [1] and may help to understand superconductivity in doped elemental semiconductors in general.

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We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga-doping levels up to 6%, not accessible to any other preparation method so far. The superconducting critical parameters strongly depend on the annealing conditions. Transport measurements reveal Tc up to 0.5 K and anisotropic Bc(T) with a linear temperature dependence reflecting the two-dimensional character of the superconducting state in the ~ 60 nm thin Ge:Ga layer. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si [1] and diamond [2], this work reports another unexpected observation of superconductivity in doped elemental semiconductors. Our fabrication techniques are compatible to industrial semiconductor processing and allow for on-chip superconductivity in integrated circuits.

Recently, superconductivity was detected in heavily boron doped group IV semiconductors like diamond (cB=2.8 at%, TC=4 K) [1] and silicon (cB=1.2 at%, TC=0.34 K) [2]. These unexpected results initiated a new debate about the possibility and the mechanism of superconductivity in doped semiconductors. Theoretical calculations, based on the classical electron-phonon coupling mechanism, demonstrated that critical temperatures in diamond can clearly exceed 1 K for acceptor concentrations higher than 5 at% [3]. However, unrealistic high doping concentrations are predicted for observable superconductivity in Si or even Ge. It was an open question whether superconductivity can be achieved in doped Ge. In order to fabricate group IV semiconductors with acceptor concentrations much higher than their equilibrium solid solubility exotic doping methods like high-pressure-high-temperature synthesis [1] or gas immersion laser doping [2] were applied. We used a more conventional doping process consisting of high dose implantation and 3 ms flash lamp or 60 s rapid thermal annealing in order to form Ge layers with Ga concentrations up to 6 at%. According to Hall effect measurements the hole concentrations are in the range between 0.3x1021 and 1.4x1021 cm-3. Superconductivity was found in the Ga-doped Ge samples below critical temperatures between 0.1 and 0.5 K in dependence on the annealing conditions. References [1] E. A. Ekimov et al., Nature 428 (2004) 542 [2] E. Bustarret et al., Nature 444 (2006) 465 [3] L. Boeri, J. Kortus, O. K. Anderson, J. Phys. Chem. Solids 67 (2006) 552

The investigation of Mn in Ge was motivated by its potential application as spintronics material. Recently various groups realized that two phases of Mn in Ge:Mn, prepared by ion implantation and MBE [1], coexist: diluted Mn ions and a Mn-rich secondary phase. Usually the Mn-rich secondary phase is believed to be responsible for the observed ferromagnetism. In this contribution, we provide direct evidence for the dilution of Mn in Ge by electrical and magneto-transport investigation. Mn ions were implanted into semi-insulating Ge wafers. We observed p-type conductivity in the implanted surface layer with the thermal activation energy similar to that of heavily doped Ge [2]. The observed anomalous Hall effect (AHE) cannot be explained by the presence of Mn5Ge3 clusters, since the AHE does not mimic the hysteresis of magnetic moments probed by SQUID. We propose that the dilution of Mn in Ge results in a large spin-splitting of the valence band, however the concentration of diluted Mn is not large enough to develop ferromagnetic coupling. [1] Appl. Phys. Lett. 88, 061907 (2006); Phys. Rev. B 77, 045203 (2008). [2] Phys. Rev. 100, 659 (1955), Phys. Rev. Lett. 91, 177203 (2003).

We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced a series of Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 6 %, i.e., a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with Tc up to 0.5 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field reflecting the two-dimensional character of the superconducting state in the ~ 60 nm thin Ge:Ga layer. We find critical magnetic in-plane fields following a linear temperature dependence up to a maximum field which is even larger than the Pauli-Clogston limit. Ge:Ga appears to be a superconductor in the extreme type-II limit with a very small Cooper-pair density. After its finding in Si [1] and diamond [2], our work reports another unexpected observation of superconductivity in doped elemental semiconductors.

In producing diluted magnetic semiconductors (DMS), it remains challenging to obtain a uniform distribution of magnetic ions. Composite ferromagnet/semiconductor systems are easily formed when the concentration of magnetic ions is larger than its solubility at given preparation conditions. This is usually considered as a failure for spintronics applications. However, as long as the embedded (nano)ferromagnets can polarize charge-carriers in the semiconducting matrix, the composite systems can also fullfill spintronics requirements. For example, nanocomposite systems with ferromagnetic MnAs nanocrystals being epitaxially embedded inside GaAs matrix reveal a giant magnetoresistance [1]. Recently, the phase separation in Mn doped Ge [2] and Si [3] has been indentified by high resolution characterization techniques. Therefore, the research interest in composite ferromagnet/semiconductor systems arises in parallel with that in DMS materials. Here we present the magnetic and magneto-transport properties of cobalt nanocrystals embedded inside carbon. Co(40%)/C nanocomposite films were prepared by ion beam co-sputtering method using silicon substrates with a 500 nm thick oxide layer. The phase separation was controlled by varing substrate temperatures from room temperature to 500 °C. We have measured their magnetic and magneto-transport properties. Two significant observations will be discussed: (i) a giant anomalous Hall effect (AHE) amounting to 2 μohm cm compared with pure Co metal [4], and (ii) a negative magnetoresistance. This encourages future applications in Hall sensors and spintronic-devices.

We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced a series of Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 6%, i.e., a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with Tc up to 0.5 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field reflecting the two-dimensional character of the superconducting state in the thin Ge:Ga layer having an effective depth of only 60 nm. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si [1] and diamond [2], our work reports another unexpected obervation of superconductivity in doped elemental semiconductors.

Outstanding scientific results and statistical overview of the Institute of Ion Beam Physics and Materials Research in 2008

We report the first observation of superconductivity in heavily p-type doped Germanium at ambient-pressure conditions. Using Ga as dopant, we have produced a series of GeGax samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 14%, i.e. a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with Tc up to 0.39 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field re ecting the two-dimensional character of the superconducting state in the thin GeGax layer having an effective depth of only 20 nm. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors.

Recently, superconductivity has been discovered in heavily boron-doped group IV semiconductors like diamond [1] and silicon [2]. Because theoretical studies predict only a weak tendency to superconductivity in heavy p-type doped Ge [3] investigations of the low-temperature transport behaviour in Ge are still lacking. In order to obtain superconductivity in group IV semiconductors, heavy p-type doping above the metal-insulator-transition and low lattice damage is required. The combination of both conditions make it difficult to apply ion implantation as doping technique. The challenge is to reconstruct the damaged or even amorphized crystal lattice and to activate the acceptor atoms after implantation by annealing, avoiding at the same time long range diffusion and precipitation of the acceptors in the supersaturated semiconductor. So far only in-situ doping during growth (high-temperature-high-pressure synthesis [1] and chemical vapour deposition) for boron-doped diamond and ultra-short-time laser melting of the Si surface in BCl3 atmosphere (gas immersion laser doping [2]) have met these conditions. Here an alternative process compatible with semiconductor technology is presented. Ga implantation and flash lamp annealing in the ms range enables the production of Ga supersaturated (up to 15 at%) crystalline Ge layers which become superconducting below 0.5 K. The layer structure investigated by AES, XTEM, RBS/C and the electrical transport properties at low temperatures are reported. [1] E. A. Ekimov, V. A. Sidorov, E. D. Bauer, et al. , Nature 428 (2004) 542 [2] E. Bustarret, C. Marcenat, P. Achatz, et al., Nature 444 (2006) 465 [3] L. Boeri, J. Kortus, O. K. Anderson, J. Phys. Chem. Solids 67 (2006) 552

High fluence P implantation (30 keV, 3x1015 cm-2) into pre-amorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. In contrast to previous assumptions a significant P diffusion in amorphous Ge is not observed. However, during the fast solid phase epitaxial regrowth a rapid redistribution of P occurs. After completion of the regrowth and at temperatures above 500 0C, a concentration-dependent diffusion of P in crystalline Ge takes place. An appreciable influence of implantation defects on the diffusion coefficient of P cannot be found. For 60 s rapid thermal annealing at 600 0C and for 20 ms flash lamp annealing at 900 0C, the junction depth and the sheet resistance vary between 140 and 200 nm and between 50 and 100 Ohm , respectively, and the maximum electrical activation of P is about 3 – 7x1019 cm-3.

There is a growing interest in graphite nanostructures since the discovery of exotic quantum properties of and the evidence for a field effect in few-layer-graphene (FLG) [1]. A promising method to produce mechanically stable and electrically isolated graphite nanostuctures is focused ion beam (FIB) implantation into diamond and subsequent annealing [2]. Graphite nanostructures with dimensions down to 100 nm, i.e. wires and electrodes including contact pads, which enable Hall and field effect measurements are produced by 30 keV Ga+ FIB implantation in a (100)- and (111)-oriented diamond surface followed by a subsequent annealing in the temperature range from 600° to 1500°C in vacuum. The structural quality and the electrical properties of the graphite nanostructures are investigated in dependence on the preparation conditions by means of AFM, SEM and electrical measuring techniques. [1] K. S. Novoselov et al. Science 306, 666 (2004) and Nature 438, 197 (2005) [2] A. M. Zaitsev and I. A. Dobrinet, phys. stat. sol. (a) 203, R35 (2006)

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