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Abstract: Ge is a very promising material as future channel materials for nanoscale MOSFETs due to its high mobility and thus a higher source injection velocity, which translates into higher drive current and smaller gate delay. However, for Ge to become main-stream, surface passivation and heterogeneous integration of crystalline Ge layers on Si must be achieved. We have demonstrated growth of fully relaxed smooth single crystal Ge layers on Si using a novel multi-step growth and hydrogen anneal process without any graded buffer SiGe layer. Surface passivation of Ge has been achieved with its native oxynitride (GeO x N y ) and high-permittivity (high-k) metal oxides of Al, Zr and Hf. High mobility MOSFETs have been demonstrated in bulk Ge with high-k gate dielectrics and metal gates. However, due to their smaller bandgap and higher dielectric constant, most high mobility materials suffer from large band-to-band tunneling (BTBT) leakage currents and worse short channel effects. We present novel, Si and Ge based heterostructure MOSFETs, which can significantly reduce the BTBT leakage currents while retaining high channel mobility, making them suitable for scaling into the sub-15nm regime. Through full band Monte-Carlo, Poisson-Schrodinger and detailed BTBT simulations we show a dramatic reduction in BTBT and excellent electrostatic control of the channel, while maintaining very high drive currents in these highly scaled heterostructure DGFETs. Heterostructure MOSFETs with varying strained-Ge or SiGe thickness, Si cap thickness and Ge percentage were fabricated on bulk Si and SOI substrates. The ultra-thin (∼2nm) strained-Ge channel heterostructure MOSFETs exhibited >4× mobility enhancements over bulk Si devices and >10× BTBT reduction over surface channel strained SiGe devices. [Copyright &y& Elsevier]

Miniaturization paradigm leads to a rapid performance deterioration of Copper wires in the future, despite lower dielectric constant materials between the lines. This work examines optical interconnects as an alternative for high performance silicon integrated circuits, and compares it with future metal interconnects. Both global signaling and clock distribution applications are considered. For clocking, power dissipation, where as, for global signaling, both power and delay are compared with metal-based interconnects. We show that for high switching activity, long global signaling wires, it is favorable to switch to optical interconnects on both power and delay account. Whereas, a metal-based interconnect system is more favorable for shorter links. [Copyright &y& Elsevier]

In this paper, a record-breaking efficiency of 12.3% is experimentally demonstrated for a flexible free-standing, 2.7-μm-thick ultrathin crystalline silicon (c-Si) solar cell, which is the highest ever-reported sub 3 μm c-Si solar cells. The first breakthrough of this study is achieving an exceptionally small exposure feature size of 350 nm using photolithography stepper without any additional stringent requirements on wafer flatness or depth of focus (DOF) of the projection system. This small exposure feature size enables the fabrication of a light-trapping scheme: a design of close-packed 700-nm-period touching inverted-pyramid nanostructures for enhanced light absorption. Furthermore, to reduce contact recombination, this work is also first to report the integration of nickel oxide (NiO x) as hole-selective contacts in conjunction with the nano-structure light trapping scheme on a free-standing ultrathin cell. The efficacy of these two mechanisms to enhance ultrathin c-Si cell efficiency is characterized in terms of the short circuit current density and open circuit voltage. The free-standing cell also shows good mechanical flexibility and compliance. In addition to demonstrating silicon-compatible fabrication, this work shows the potential of ultrathin c-Si technology to not only reduce material cost, but also maintain competitive device performance. Image 1 • Free-standing sub 3 μm ultrathin c-Si cell with high efficiency above 12.0%. • Close-packed 700 nm feature size nanostructure light trapping by photolithography. • Integration of both NiO x hole-selective contact and light trapping. [ABSTRACT FROM AUTHOR]

A technique to locally grow germanium-on-insulator (GOI) structure on silicon (Si) platform is studied. On (001) Si wafer, silicon dioxide (SiO 2 ) is thermally grown and patterned to define growth window for germanium (Ge). Crystalline Ge is grown via selective hetero-epitaxy, using SiO 2 as growth mask. Lateral overgrowth of Ge crystal covers SiO 2 surface and neighboring Ge crystals coalesce with each other. Therefore, single crystalline Ge sitting on insulator for GOI applications is achieved. Chemical mechanical polishing (CMP) is performed to planarize the GOI surface. Transmission electron microscopy (TEM) analysis, Raman spectroscopy, and time-resolved photoluminescence (TRPL) show high quality crystalline Ge sitting on SiO 2 . Optical response from metal–semiconductor–metal (MSM) photodetector shows good optical absorption at 850 nm and 1550 nm wavelength. [ABSTRACT FROM AUTHOR]

Abstract: We report on the characterization of high Sn-content (∼10% Sn) GeSn films grown on (001) Ge/Si substrates using reduced-pressure chemical vapor deposition. Pseudomorphic 30nm GeSn films were grown on relaxed Ge buffers, exhibit a smooth surface, and display strong photoluminescence (PL) with cavity-resonance fringes from the Ge buffer. Additional luminescence studies confirm that the measured PL originates from the GeSn film. A study on the effects of rapid thermal annealing is presented along with evidence of Sn surface segregation and formation of surface nanodots for anneals at 450°C and above. Anneals at 400°C for up to 500s showed little change in PL intensity or material properties, which suggest that a critical temperature exists for post-growth thermal-processing of high Sn-content, compressively-strained GeSn films. [Copyright &y& Elsevier]

Abstract: In X Ga1− X Sb has the highest hole mobility amongst all III–V semiconductors which can be enhanced further with the use of strain. The use of confinement and strain in In X Ga1− X Sb quantum wells lifts the degeneracy between the light and heavy hole bands which leads to reduction in the hole effective mass in the lowest occupied band and an increase in the mobility. We present magnetotransport measurements on compressively strained In X Ga1− X Sb and GaSb quantum wells. Hall-bar and Van de Pauw structures were fabricated and Shubnikov–de Haas oscillations in the temperature range of T =2–10K for magnetic fields of B =0–9T were measured. The reduction of effective hole mass with strain was quantified. These results are in excellent agreement with modeling results from band structure calculations of the effective hole mass in the presence of strain and confinement. [Copyright &y& Elsevier]