Search

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

In this work, we report on non-equilibrium processing for controlled doping of Si/SiO2 core/shell nanowires with shallow- and deep-level dopants below and above their equilibrium solid solubility. In detail, the shallow-level dopants B and P as well as the deep-level dopant Se was implanted, followed by millisecond flash lamp annealing. In case of amorphization upon high-fluence implantation, recrystallization takes place via a bottom-up template-assisted solid phase epitaxy. Non-equilibrium Se concentrations lead to the formation of an intermediate band in Si which in turn causes a room-temperature sub-band gap photoresponse of the nanowire when configured as a photoconductor device [1]. Alternatively, the formation of a cross-sectional p-n junction is demonstrated by co-implanting P and B in individual nanowires at different depth along the NW core. [1] Y. Berencén, et al. Adv. Mater. Interfaces 2018, 1800101

There is a broad palette of applications for thin Si and Ge films ranging from photovoltaics over various microelectronic devices to sensor applications. Both amorphous and polycrystalline thin films are of interest for thin film photovoltaics, and thin film poly-Si transistors are the heart piece for driving LCDs and OLEDs [1]. In addition, the ability to deposit SiO2 and Si layers in an alternating order and to process them allows to extend the device density without further downscaling [2]. Amorphous thin film deposition methods are the most cost-effective ones, the subsequent crystallization is the most critical process step with regard to microstructure, defect density, and electrical properties. Potentially, flash lamp annealing (FLA) is a very suitable method due to the short process time, the qualification for temperature-sensible substrates and the possibility to take advantage of non-equilibrium crystallization modes [3]. In this work thin amorphous Si and Ge films have been deposited on SiO2 by DC-magnetron sputtering and crystallized by in-situ FLA in a new FLA sputter tool recently installed by the Rovak GmbH at HZDR (Fig. 1). The in-situ-processing suppresses the influence of surface oxidation effects after deposition prior to FLA. In order to investigate the crystallization behaviour, the thin films have been characterized by Raman spectroscopy, X-ray diffraction, ellipsometry, current-voltage and Hall effect measurements. Based on these results and in combination with temperature simulations, a model for the crystallization of thin amorphous Si and Ge films is derived.

Der Vortrag stellt das Helmholtz Innovation Lab für Ultrakurzzeitausheilung vor. Im zweiten Teil werden experimentelle Ergebnisse bei der Kristallisation von dünnen amorphen Halbleiterschichten (Si, Ge, NiGe) mittels magnetron sputtering und Blitzlampenausheilung diskutiert.

The last missing piece of puzzle for the full functionalization of group IV optoelectronic devices is the direct band gap semiconductor made by CMOS compatible technology. Here we report on the fabrication of GeSn alloys with a Sn concentration of up to 6 % using ion implantation followed by ms-range explosive solid phase epitaxy. The n-type single crystalline GeSn alloys are made by co-doping of Sn and P into Ge. Both the activation of P and the formation of GeSn are performed during a single-step flash lamp annealing for 3 ms. The band gap engineering in ultra-doped n-type Ge and GeSn alloys is theoretically predicted by density functional theory and experimentally verified using ellipsometric spectroscopy. We demonstrate that both the diffusion and the segregation of Sn and P atoms in Ge are fully supressed by ms-range non-equilibrium thermal processing.

Pipe organs with their unique musical sound are important objects of the cultural heritage. Such instruments consist of a number of pipes (flute and reed), which are prone to heavy corrosion attack, getting finally voiceless. The atmospheric corrosion of reed (CuZn alloys) and flute pipes (PbSn alloys) is strongly enhanced by traces of volatile organic compounds (VOCs) and the alloy’s instability. Moreover, there is a strong impact of humidity in the corrosion process. Experiments have been undertaken to explore the suppression of an aqueous corrosion with acetic acid concentration (2–5 v/v%) of CuZn and PbSn alloys, by deposition of nanocoating using two different methods: (i) Pulsed laser- or Magnetron sputtering deposition of Al2O3 or Al followed by plasma immersion ion implantation of nitrogen as a vacuum technology, and (ii) Plasma enhanced CVD of SiOx films at atmospheric pressure. The nanocoating is then able to withstand acoustic vibrations of organ pipes, and it produces a barrier to VOCs and water vapor. The laboratory corrosion tests were combined with field studies to approach environmental conditions. Some of the samples were exposed for 15 months to harmful indoor environment in North-German church. Surface modification of metallic alloys based on ion-solid interactions as well as plasma-based processing creates new paths in restoration and conservation technologies to protect our historical and modern cultural heritage against environmental attacks.

Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low electron effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that both the millisecond range flash lamp annealing (solid phase epitaxy) and nanosecond range pulsed laser annealing (liquid phase epitaxy) are able to recrystallize the implanted layers and electrically activate dopants. The carrier concentration in the heavily doped p- and n-type GaAs is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained GaAs films display a room-temperature plasma frequency above 2200 cm-1, which makes GaAs attractive for sensing in the mid-infrared spectral range.

Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that either the millisecond range flash lamp annealing (solid phase epitaxy) or nanosecond range pulsed laser annealing (liquid phase epitaxy) is able to recrystallized the implanted layers and electrically activate the dopants.The carrier concentration in the heavily doped p- and n-type GaAs with sub-second annealing treatment is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained ultra-highly GaAs films display a room-temperature plasma frequency above 2200 cm-1, which enables to exploit the plasmonic properties of GaAs for sensing in the mid-infrared spectral range.