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We report detailed Raman and photoluminescence (PL) measurements in Si/Si1−xGex nanostructures grown by molecular-beam epitaxy under conditions of near Stranski–Krastanov (S-K) growth mode. In a series of samples with x controllably increased from 0.098 to 0.53, we observe that an increase in Raman signal related to Ge–Ge vibrations clearly correlates with (i) a redshift in the PL peak position, (ii) an increase in the activation energy of PL thermal quenching, and (iii) an increase in the PL quantum efficiency. The results indicate that in S-K Si/Si1−xGex nanostructures with x>0.5 Ge atoms form nanometer-sized clusters with a nearly pure Ge core and a SiGe shell.

Using polarized Raman spectroscopy, we examine different vibrational modes (i.e., Si–Si, Si–Ge, and Ge–Ge) in Si/Ge self-organized nanostructures. Here, we present unambiguous proof that multilayers of Ge nanometer-size, “dome-shaped” islands grown on a 〈100〉 Si substrate are nearly fully relaxed and that the built-in strain field is substantially localized in the surrounding Si matrix. In contrast, multilayers with “pyramid-shaped” islands do not show observable relaxation. The large strain in the Si layers of the multilayer dome samples correlates with the greater self-organization in these structures compared to the multilayer pyramid samples.

We report an original analysis method to model the p-polarized infrared reflectivity (IR) spectra of (GaAs)m/(AlAs)n superlattices (m=36, 4

We report on the interface quality and phonon-assisted tunneling in nanocrystalline Si (nc-Si)/amorphous SiO2 (a-SiO2) superlattices (SLs) prepared by magnetron sputtering and thermal crystallization of nanometer-thick a-Si layers. Phonon-assisted tunneling is observed in a bipolar nc-Si based structure, which confirms that the nc-Si/a-SiO2 junction is not only abrupt but also nearly defect free. The conclusion is supported by capacitance–voltage measurements from which the estimated interface defect density is found to be ∼1011 cm−2 for an eight-period SL. Such high quality interfaces hold considerable promise for the development of nc-Si SL quantum devices.

Pore growth on n-type GaAs (100) can be initiated in 1 M HCl solution by electrochemical polarization of the material anodic to a critical potential value—the pore formation potential (PFP). At surface defects, however, the PFP is significantly lower (shifted cathodically). Focused ion beam, implantation of Si++ was used to create defined patterns in the substrate. At these implant sites, the growth of porous GaAs was selectively achieved by polarization below the overall PFP. From the porous GaAs patterns visible photoluminescence at green-yellow wavelengths can be observed. This technique, thus, allows the production of light emitting porous GaAs micropatterns of arbitrary shape by a direct writing process.

We report a structural study of partially relaxed, 0.1‐μm‐thick, In1−xAlxSb (0.15

Germanium buried layers in (001) oriented silicon with thicknesses of 2–12 monolayers have been studied with synchrotron x‐ray diffraction, x‐ray reflectivity, and Raman scattering spectroscopy of visible light. Relaxation, strain, and intermixing have been observed via diffraction and intermixing is inferred from vibrational frequency shifts.

Epitaxial (111)CdxPb1−xTe//(111)BaF2 films in the rocksalt structure have been made by codeposition from CdTe and PbTe magnetron targets in an rf discharge onto chemipolished substrates at 320 °C. Films were prepared with x values from 0 to 0.47, well past the range of bulk thermodynamic solubility. Raman spectroscopy, Auger spectroscopy, and transmission electron microscopy showed phase segregation had not occurred. The lattice spacing in the growth direction was observed to be insensitive to x.

An intense photoluminescence (PL) peaking near 0.9 eV is emitted by a single Si1-xGex nanometer-thick layer (NL) with x ≈ 8% incorporated into Si/Si0.6Ge0.4 cluster multilayers (CMs). The SiGe NL PL does not saturate in output intensity with up to 50 mJ/cm^2 of excitation energy density, and it has nearly a 1000 times shorter lifetime compared to CM PL, which peaks at ∼0.8 eV. These dramatic differences in observed PL properties are attributed to different compositions and structures of the Si/SiGe NL and CM hetero-interfaces.

We show that strain, arising from the mismatch between Si and SiO₂ thermal expansion coefficients, directs the thermal crystallization of amorphous Si along Si/SiO₂ interfaces, and produces continuous, fully crystallized nanometer thick Si layers with a lateral-to-vertical aspect ratio close to 100:1. These Si nanolayers exhibit a low density of structural defects and are found to be elastically strained with respect to the crystal Si substrate.

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.

We study the role that the growth temperature plays in determining the amount of order present within silicon films deposited on fused silica substrates through ultrahigh-vacuum evaporation at growth temperatures ranging from 98 to 572°C. Through measurements of the Raman and optical absorption spectra, we quantitatively determine how the growth temperature influences the order present within 11 such films. We employ three disparate measures of order for the purposes of this study: the breadth of the transverse-optic phonon Raman peak, this being related to the amount of short-range order present; the area under the transverse-acoustic Raman peak divided by the area under the corresponding transverse-optic peak, this being related to the amount of intermediate-range order present; and the breadth of the optical absorption tail, which is a general measure of the overall amount of order present. All three measures of order indicate a dramatic increase in the amount of order present for growth temperatures a...

GemSin ultrathin superlattices have been grown on (001) Si substrates and partly capped with Si. Raman scattering from acoustic phonons in the long‐wavelength region shows unexpectedly intense broad peaks that develop into an increased number of sharper intense peaks on capping. We identify these peaks with resonant phonon modes and use a linear chain model to expose the importance of substrate‐superlattice‐capping layer interactions in these multilayer structures.

The excitation of zone‐folded longitudinal acoustic phonons in GaAs/InxGa1−xAs strained‐layer superlattices is observed by Raman scattering. The Raman data agree well with theory and are consistent with high indium concentrations achieved in the fabrication of these metastable superlattices of good crystalline quality.