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An electroabsorption modulator using a side-entry architecture achieved a contrast ratio exceeding 3 dB over a 3.5 nm range in the C-band, using a voltage swing of 1 V and operating at 100°C. Modulation was due to the quantum-confined Stark effect from ten Ge/SiGe quantum wells epitaxially grown on silicon-on-insulator (SOI) wafers. The device exploits an asymmetric Fabry-Perot resonator formed between the totally internally reflecting air-SiGe interface and a frustrated total internal reflection from the buried oxide layer of the SOI substrate. [ABSTRACT FROM AUTHOR]

Unstrained Ge1-xSnx layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge0.97Sn0.03 layers with built-in compressive (ε=-0.5%) and tensile (ε=0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photo-reflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For unstrained Ge1-xSnx layers, the pressure coefficient for the direct band gap transition is determined from PR measurements at various hydrostatic pressures to be 12.2±0.2meV/kbar, which is very close to the pressure coefficient for the direct band gap transition in Ge (12.9 meV/kbar). This suggests that the hydrostatic deformation potentials typical of Ge can be applied to describe the pressure-induced changes in the electronic band structure of Ge1-xSnx alloys with low Sn concentrations. The same conclusion is derived for the uniaxial deformation potential, which describes the splitting between heavy-hole (HH) and light-hole (LH) bands as well as the strain-related shift of the spin-orbit (SO) split-off band. It is observed that the HH, LH, and SO related transitions shift due to compressive and tensile strain according to the Bir-Pikus theory. The dispersions of HH, LH, and SO bands are calculated for compressive and tensile strained Ge0.97Sn0.03 with the 8-band kp Hamiltonian including strain effects, and the mixing of HH and LH bands is discussed. In addition, the dispersion of the electronic band structure is calculated for unstrained Ge1-xSnx layers (3% and 6% Sn) at high hydrostatic pressure with the 8-band kp Hamiltonian, and the pressure-induced changes in the electronic band structure are discussed. [ABSTRACT FROM AUTHOR]

We find that in Si/SiGe three-dimensional multilayer nanostructures, photoluminescence intensity as a function of temperature depends on the excitation intensity. The experimental results are explained using a model where electron-hole separation and nonradiative recombination is controlled by a competition between hole tunneling and thermally activated hole diffusion over the valence band energy barriers at Si/SiGe heterointerfaces. [ABSTRACT FROM AUTHOR]

The mechanical resonance of laterally grown silicon nanowires measured by an optical interferometric technique is reported. The lengths and diameters of the nanowires ranged from L=2 to 20 μm and D=39 to 400 nm, respectively. The wires showed resonant frequencies in the f0=1–12 MHz range and resonant quality factors Q at low pressure ranging from Q=5000 to Q=25 000. The dependence of resonant frequency on the ratio of diameter to length squared, D/L2, yielded a ratio of E/ρ=9400±450 m/s. Assuming a density of ρ=2330 kg/m3, this experimental result yields an experimental Young modulus of E=205±10 GPa, consistent with that of a bulk silicon. As the wires were cooled from T=270 K to T=77 K, a 0.35% increase of resonant frequency was observed. This increase of resonant frequency with cooling resulted from a change in Young’s modulus and from the thermal contraction of silicon. The quality factor did not vary significantly from P=10-4 to 102 Torr, suggesting that viscous damping does not dominate the dissipative processes in this pressure range. Although viscous damping became important above P=102 Torr, relatively high quality factors of Q=7000 were still observed at atmospheric pressure. [ABSTRACT FROM AUTHOR]

Low impedance and negligible conductivity temperature dependence are found for micron-long Ge nanowires (NWs) grown on (p+)Si substrates. In contrast, Ge NW/(n+)Si substrate samples exhibit many orders of magnitude higher impedance, an exponential dependence of conductivity on temperature, current instabilities, and negative differential photoconductivity. Our experimental results are explained by a model that considers energy-band alignment and carrier transport in abrupt Ge NW/Si substrate heterojunctions. [ABSTRACT FROM AUTHOR]

Silicon–germanium epitaxially grown on silicon in the form of two-dimensional (quantum wells) and three-dimensional (quantum dots) nanostructures exhibits photoluminescence and electroluminescence in the technologically important spectral range of 1.3–1.6 μm. Until recently, the major roadblocks for practical applications of these devices were strong thermal quenching of the luminescence quantum efficiency, and a long carrier radiative lifetime. This paper summarizes recent progress in the understanding of carrier recombination in Si/SiGe nanostructures and presents a potential new route toward CMOS compatible light emitters for on-chip optical interconnects. [ABSTRACT FROM AUTHOR]

In crystalline, dislocation-free, Si/Ge nanowire axial heterojunctions grown using the vapor-liquid-solid technique, photoluminescence and Raman spectroscopy reveal a SiGe alloy transition layer with preferential chemical composition and strain. In addition to the lattice mismatch, strain in Si/Ge nanowires is observed from a temperature dependent study to be affected by the difference in Si and Ge thermal expansion. The conclusions are supported by analytical transmission electron microscopy measurements. [ABSTRACT FROM AUTHOR]

In Ge/Si Stranski-Krastanov nanostructures grown by chemical vapor deposition, the authors find ∼30 meV/decade photoluminescence (PL) spectral shift toward greater photon energies as excitation intensity increases from 0.1 to 104 W/cm2. The PL lifetime exhibits strong spectral dependence, and it decreases from ∼20 μs at 0.77 eV to 200 ns at 0.89 eV. The authros attribute the observed PL spectral shift and shorter PL lifetime at higher photon energies to an increasing contribution from recombination between holes populating excited Ge cluster energy states and electrons in SiGe alloy cluster regions. [ABSTRACT FROM AUTHOR]

The heteroepitaxial growth of III-V compound semiconductors on Si would enable the integration of high-performance III-V materials with Si technology. We report epitaxial growth on (111)-oriented Si surfaces of highly aligned, single crystalline InP nanowires by chemical vapor deposition catalyzed by Au. We demonstrate laterally oriented InP nanowires bridging between vertical (111) Si surfaces formed by anisotropically etching a (110)-oriented Si substrate or the top Si layer of a silicon-on-insulator wafer. This method of connecting nanowires offers a facile way of integrating nanoscale III-V optoelectronic and photonic devices with Si. [ABSTRACT FROM AUTHOR]

Mechanical properties of self-welded [111] single-crystal silicon nanowire bridges grown between two silicon posts using metal-catalyzed chemical vapor deposition were determined using both dynamic and static measurements. The static tests were carried out using atomic force microscopy (AFM) to measure the nanowires’ Young’s modulus and the strength of the self-welded junctions. The AFM-measured Young’s modulus ranged from 93 to 250 GPa (compared to 185 GPa for bulk silicon in the [111] direction) depending on the nanowire diameter, which ranged from 140 to 200 nm. The self-welded wire could withstand a maximum bending stress in the range of 210–830 MPa (larger than bulk silicon), which also depended on the nanowire diameter and loading conditions. The beam broke close to the loading point, rather than at the self-welded junction, indicating the excellent bond strength of the self-welded junction. The vibration spectra measured with a network analyzer and a dc magnetic field indicated a dynamic Young’s modulus of 140 GPa, in good agreement (within the experimental error) with the static measurement results. [ABSTRACT FROM AUTHOR]