Federica Gencarelli

Undoped and in-situ B doped GeSn epitaxial growth on Ge by atmospheric pressure-chemical vapor deposition

In this letter, we propose an atmospheric pressure-chemical vapor deposition technique to grow metastable GeSn epitaxial layers on Ge. We report the growth of defect free fully strained undoped and in-situ B doped GeSn layers on Ge substrates with Sn contents up to 8%. Those metastable layers stay fully strained after 30 min anneal in N2 at 500 °C; Ge-Sn interdiffusion is seen at 500 °C but not at lower temperature. B is 100% active in the in-situ GeSn:B layers up to a concentration of 1.7 × 1019 cm−3. GeSn:B provides slightly lower Hall hole mobility values than in pure p-type Ge especially for low B concentrations.

GeSn/Ge heterostructure short-wave infrared photodetectors on silicon

A surface-illuminated photoconductive detector based on Ge0.91Sn0.09 quantum wells with Ge barriers grown on a silicon substrate is demonstrated. Photodetection up to 2.2µm is achieved with a responsivity of 0.1 A/W for 5V bias. The spectral absorption characteristics are analyzed as a function of the GeSn/Ge heterostructure parameters. This work demonstrates that GeSn/Ge heterostructures can be used to developed SOI waveguide integrated photodetectors for short-wave infrared applications.

Silicon-Based Photonic Integration Beyond the Telecommunication Wavelength Range

In this paper we discuss silicon-based photonic integrated circuit technology for applications beyond the telecommunication wavelength range. Silicon-on-insulator and germanium-on-silicon passive waveguide circuits are described, as well as the integration of III-V semiconductors, IV-VI colloidal nanoparticles and GeSn alloys on these circuits for increasing the functionality. The strong nonlinearity of silicon combined with the low nonlinear absorption in the mid-infrared is exploited to generate picosecond pulse based supercontinuum sources, optical parametric oscillators and wavelength translators connecting the telecommunication wavelength range and the mid-infrared.

Silicon-based heterogeneous photonic integrated circuits for the mid-infrared

In this paper we present our recent work on mid-infrared photonic integrated circuits for spectroscopic sensing applications. We discuss the use of silicon-based photonic integrated circuits for this purpose and detail how a variety of optical functions in the mid-infrared besides passive waveguiding and filtering can be realized, either relying on nonlinear optics or on the integration of other materials such as GaSb-based compound semiconductors, GeSn epitaxy and PbS colloidal nanoparticles.

Towards high mobility GeSn channel nMOSFETs: Improved surface passivation using novel ozone oxidation method

We present a detailed theoretical analysis to motivate GeSn for CMOS logic. High quality GeSn films have been obtained on Ge-on-Si using a CVD process. A novel surface passivation scheme is presented to achieve record low trap densities at high-κ/GeSn interface. Using the novel surface passivation method, combined with a low thermal budget device fabrication process, n-channel MOSFETs on GeSn with channel Sn content as high as 8.5% have been demonstrated for the first time.

GeSn channel nMOSFETs: Material potential and technological outlook

Semiconducting germanium tin (GeSn) alloy has recently emerged as a candidate for optoelectronic and high performance CMOS devices because of its tunable direct gap and potential for high electron and hole mobilities. High hole mobility in GeSn channel pMOSFETs has already been demonstrated [1, 2]. However, GeSn as channel for nMOSFETs has not yet been explored. In this work we perform detailed theoretical analysis to gauge the benefits of GeSn channel over Ge for nMOSFETs. Our analysis predicts GeSn nMOSFETs to outperform Ge. GeSn n-channel devices have been successfully fabricated and factors limiting its performance.

Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1−xSnx films

We present an extended X-ray absorption fine structure investigation of the local environment of Sn atoms in strained and relaxed Ge1−xSnx layers with different compositions. We show that the preferred configuration for the incorporation of Sn atoms in these Ge1−xSnx layers is that of a α-Sn defect, with each Sn atom covalently bonded to four Ge atoms in a classic tetrahedral configuration. Sn interstitials, Sn-split vacancy complexes, or Sn dimers, if present at all, are not expected to involve more than 2.5% of the total Sn atoms. This finding, along with a relative increase of Sn atoms in the second atomic shell around a central Sn atom in Ge1−xSnx layers with increasing Sn concentrations, suggests that the investigated materials are homogeneous random substitutional alloys. Within the accuracy of the measurements, the degree of strain relaxation of the Ge1−xSnx layers does not have a significant impact on the local atomic surrounding of the Sn atoms. Finally, the calculated topological rigidity parame...

On the interplay between relaxation, defect formation, and atomic Sn distribution in Ge(1−x)Sn(x) unraveled with atom probe tomography

Ge(1−x)Sn(x) has received a lot of interest for opto-electronic applications and for strain engineering in advanced complementary-metal-oxide-semiconductor technology, because it enables engineering of the band gap and inducing strain in the alloy. To target a reliable technology for mass application in microelectronic devices, the physical problem to be addressed is to unravel the complex relationship between strain relaxation (as induced by the growth of large layer thicknesses or a thermal anneal) and defect formation, and/or stable Sn-cluster formation. In this paper, we study the onset of Sn-cluster formation and its link to strain relaxation using Atom Probe Tomography (APT). To this end, we also propose a modification of the core-linkage [Stephenson et al., Microsc. Microanal. 13, 448 (2007)] cluster analysis method, to overcome the challenges of limited detection efficiency and lateral resolution of APT, and the quantitative assessment for very small clusters (<40 atoms) embedded in a random distr...

Atomic insight into Ge1−xSnx using atom probe tomography

Ge(1-x)Sn(x) is receiving a growing interest in the scientific community, as it has important applications in opto-electronic devices, ( as stressor) Source/Drain materials for Ge and SiGe MOSFETS. It is predicted that at 10% Sn concentration or even lower, unstrained Ge(1-x)Sn(x) will exhibit a direct band gap. Moreover, in strained Ge(1-x)Sn(x) the expected concentration of Sn for this cross-over is even lower. As the theoretical Sn incorporation in Ge(1-x)Sn(x) is less than 1%, and Ge(1-x)Sn(x) is prone to relaxation, routes towards the growth of metastable strained films has been extensively explored. Although Ge(1-x)Sn(x) films (with x up to 10%) have been grown using various methods like molecular beam epitaxy, CVD growth etc. there remain issues with tendency of these layers to relax. Detailed studies on the relaxation mechanisms and effects on the Sn-atoms require suitable characterization techniques. Various techniques have been used to study the surface of the film, crystallography or concentration of Sn in the film but none of them provides information at the atomic scale as they average over many layers and atoms. Atom probe tomography (APT) analysis, on the other hand, is one such method that can provide atomic scale resolutions (∼0.3 nm) due to its ability to perform atom by atom analysis. In this paper we explore the use of APT for characterizing Ge(1-x)Sn(x) layers. We comment on the difference of field evaporation values of Ge and Sn in Ge(1-x)Sn(x) layer by taking a closer look at the co-evaporation of the two elements and comment on the accuracy of depth reconstruction of APT for Ge(1-x)Sn(x) layer. Comparing the Sn-distributions and their local surroundings we saw a tendency for the Sn to locally enrich forming Sn clusters. Higher order clusters were observed for the relaxed sample.

(Invited) GeSn Technology: Impact of Sn on Ge CMOS Applications

S. Zaima, O. Nakatsuka, Y. Shimura, S. Takeuchi, B. Vincent, F. Gencarelli, T. Clarysse, J. Demeulemeester, K. Temst, A. Vantomme, M. Caymax, and R. Loo Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Research Fellow of the Japan Society for the Promotion of Science Covalent Silicon Co., Higashikou, Seirou-machi, Kitakanbara-gun, Niigata 957-0197, Japan imec, Kapeldreef 75, B-3001 Leuven, Belgium Instituut voor Kernen Stralingsfysica, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium