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Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge-Sn alloys. The heavily doped n-type Ge-Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge-Sn layers and to modify the lattice parameter of P-doped Ge-Sn alloys. The strain engineering in heavily-P-doped Ge-Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge-Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1x10^20 cm-3 the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology., 20 pages, 6 figures

Physical scaling down of field effect transistors (FET) is reaching its end. To meet the consistent demand for faster, smaller and energy efficient transistors, new concepts which include new materials, new architectures, new computation principles and enhanced functionality are under research. Focus of this work is to fabricate devices with enhanced functionality, the so called reconfigurable FET (RFET) which can be configured as p- or n-channel FET. These FETs are realized by fabricating silicon nanowires (SiNWs) on Si on insulator (SOI) substrates. These NWs are subsequently nickel silicided at both ends to form Si-NiSi2-Si Schottky junctions. Control over silicide length is important to scale Si channel and to have symmetric contacts on both sides of nanowires. Focus of our recent work is achieve this control over silicidation by using flash lamp annealing (FLA). Comparison between silicidation using flash lamp annealing (FLA) and rapid thermal annealing (FLA) along with the resulting electrical characteristics of these devices will be presented at the conference.

Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p- and n-type doped regions for both planar and tri-dimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1 × 10^19 cm−3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3 × 10^15 cm−2 and electron concentration of about 4 × 10^19 cm−3. The optical and structural properties of ion-implanted GeSn layers are comparable with the in situ doped MBE grown layers.

Classical scaling down of CMOS technology is reaching its end in the next few years. To facilitate further the enhancement in the complexity and performance of electronic circuits without increasing the chip area, devices with new materials, new architectures, enhanced functionality and new computation principles have gained importance. Our work focuses on fabricating devices with new architectures and enhanced functionality i.e. devices which can be reconfigured as a p- or n-channel field effect transistor (FET). These reconfigurable FETs are based on Silicon (Si) nanowires (NWs), which are silicided at both ends to form Si-NiSi2-Si Schottky junctions. Formation of NiSi2 is a pre-requisite for proper functioning of these devices since fermi level of NiSi2 aligns itself near the mid-bandgap of Si, thereby enabling tuning of band by application of electrostatic potential for its function as a p/n FET [1]. Moreover, control over silicide length is also important to scale the Si channel and to have symmetric contacts on both sides of the nanowire [2]. These issues are the focus of our recent work. In this paper, we report on comparison between silicidation of undoped Si NWs using rapid thermal annealing (RTA) and flash lamp annealing (FLA). The nanowires are fabricated on silicon on insulator (SOI) substrates by a top down process based on electron beam lithography (EBL) and subsequent inductively coupled plasma (ICP) etching. Hydrogen silsesquioxane (HSQ), a negative tone EBL resist, is used to provide high quality sub-15nm lithographic nanowire patterns, which are transferred into SOI by optimised ICP etching based on C4F8/SF6/O2 mixed gas chemistry. Subsequently, nickel (Ni) is sputtered at lithographically defined areas followed by RTA, which yields atomically sharp NiSi2-Si Schottky junctions. However, the main drawback of this silicidation process is the poor control over Ni silicide phase formation and the progression length of the silicidation along the Si NWs (Fig. 1). These effects lead to an inhomogeneous silicidation process, which prevents symmetric Si channel formation and downscaling. To provide better control over the silicidation process, a ms-range FLA is investigated as a potential replacement of RTA. Initially, the FLA was performed for 3, 6 and 20 ms on bulk silicon by either flashing the front (f-FLA) or rear (r-FLA) side of the samples. Formation of NiSi and the composition was investigated by micro-Raman (Fig. 2) and Rutherford Backscattering Spectrometry (RBS) (Fig. 3). It is shown that after 6 and 20 ms annealing 50 nm Ni is fully converted to stoichiometric NiSi with atomically sharp interface between NiSi and Si. Cubic NiSi displays Raman active phonon modes at 193 and 217 cm-1, which suggests that the fabricated layer is tensile strained. These preliminary results on bulk Si suggest that the FLA promises to provide better control over silicidation process of the nanowires, thereby enhancing the performance of reconfigurable FETs. Results on silicidation of nanowires will be presented at the conference.

GeSn with quasi-direct band gap is one of the most promising semiconductor materials for light emitters integrated with CMOS technology. The equilibrium solid solubility limit (SSL) of Sn in Ge is in the range of 0.5 % and the predicted theoretical Sn concentration needed for the direct band gap formation is above 5 %. This means that GeSn with direct band gap is metastable and any related material process cannot be thermal equilibrium. Here we propose to utilize strongly non-equilibrium processing i.e. ion implantation followed by millisecond range flash lamp annealing (FLA), for doping and the formation of Ohmic contacts with low contact resistance on Ge0.95Sn0.05. The effective carrier concentration in P+ implanted Ge0.95Sn0.05 layer followed by FLA for 3 ms is above 5×10^19cm-3 with a specific contact resistance rc=4×10^-6Ωcm2. NiGe for Ohmic contact is made by Ni diffusion into GeSn during a single 3 ms long flash pulse. TEM images reveal that NiGe is polycrystalline but with an atomically sharp interface between the metal contact and GeSn. The influence of non-equilibrium processing (ion implantation and FLA) on the optical, electrical and microstructural properties of the GeSn layer grown by MBE on Si will be discussed in details.

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).

Exploiting plasmonics for mid-IR sensing purposes has become an increasing area of research. The reason is that many molecules present molecular vibrational resonances, which provide spectral fingerprints in the near- and mid-IR region [1, 2]. Of particular interest is the gas detection, diagnostic and medical care. To this day, strong plasmon resonances in the visible and near-IR spectral range have been identified in nanostructured metals such as silver, aluminum and gold [3]. In principle, heavily doped semiconducting materials like Si or Ge could be an interesting alternative to replace metals due to their compatibility with CMOS technology. Indeed, the possibility to control the plasmon resonance frequency in semiconductors via the carrier density opens new route for near- and mid-IR detectors. In this work, we report on the strong mid-IR plasmon absorption from heavily P-doped Ge thin films obtained by non-equilibrium thermal processing. Ultra-doped Ge layers were fabricated by ion implantation of P ions followed by rear-side flash lamp annealing in the millisecond range. This approach, in contrast to conventional annealing procedures, leads to full recrystallization of Ge films and high P activation irrespective of pre-treatment. In this way, single crystalline Ge thin films free of defects with carrier concentration much above 1×1020 cm-3 and carrier mobility above 260 cm2/(V·s) were obtained. The mid-IR plasmon spectral response at room temperature from those samples was characterized by means of Fourier transform infrared spectroscopy. It is proven that the position of the signal from the plasmon resonance frequency can be tuned as a function of the P concentration. Keywords: plasmonics, heavily doped n-type Ge, flash-lamp annealing. [1] A. G. Brolo, Nat. Photonics 6, 709 (2012). [2] N. Liu, M. Mesch, T. Weiss, M. Hentschel, and H. Giessen, Nano Lett. 10, 2342 (2010). [3] G. Konstantatos and E. H. Sargent, Nat. Nanotechnology 5, 391 (2010).

The incorporation of different functional optoelectronic elements on a single chip enables performance progress, which can overcome the downsizing limit in silicon technology. For example, the use of Ge instead of silicon as a basic material in nanoelectronics would enable faster chips containing smaller transistors. In order to improve the device performance and fully exploit the unique properties of germanium, the germanium on insulator (GeOI) structure using the ultrathin body (UTB) GeOI architecture with an active doping concentration above 6×1019 cm-3 has to be explored. Here we present a new concept for the development, optimisation and fabrication of high-mobility channel materials based on Ge using plasma enhanced chemical vapour deposition of Ge and its recrystallization via millisecond range lateral explosive epitaxy. It is shown that the mechanism of explosive recrystallization (solid vs liquid) can be controlled by Sn co-doping and/or varying the annealing time. An influence of the explosive recrystallization and co-doping of Sn on the dopant activation efficiency and the carrier distribution in the ultra-thin GeOI and Ge NWs after millisecond range flash lamp annealing is discussed. Finally, the nanowire FETs will be presented. - See more at: http://www.european-mrs.com/2015-spring-symposium-z-european-materials-research-society#sthash.fI9UKy1b.dpuf