Formation and structural features of silicon quantum dots in germanium

The formation of Si quantum dots on Ge is studied. Fundamental differences were found between the nucleation and growth of quantum dots on substrates with different orientations, related to both the formation of a SiGe solid solution layer and the shape of quantum dots. The temperature interval of formation of Si nanocrystals on Ge (111) is determined. It is shown that a change in the epitaxy temperature from 480 to 400 °C increases the silicon content in quantum dots from 58 to 75%. The effect of surfactants (in particular, hydrogen) on the nucleation and growth of silicon nanoislands is analyzed, showing that the use of hydrogen as a surfactant leads to a decrease in the size of quantum dots and a substantial increase in their density. The observed effects are attributed to the suppression of surface diffusion of atoms in the presence of hydrogen.     

SiGe quantum rings on the Si(100) surface

Results of experimental studies of forming SiGe nanometer-size rings on the Si(100) surface by the molecular-beam epitaxy method are presented. Detailed shapes and size distributions of the grown nanorings are studied by the atomic-force microscopy method. The elemental composition is determined by the Raman scattering method. The average germanium content in the nanorings was 37% for a forming temperature of 680°C. The obtained data on the geometry and composition of the produced nanostructures were used for calculations by the 6-band k × p-method of the energy spectrum and charge density distribution of hole states, localized on the SiGe quantum rings embedded in the Si-matrix. It is shown that the heterostructures with quantum SiGe rings are promising objects for creating devices that are capable of detecting electromagnetic radiation in terahertz and infrared wavelength ranges.     

Ordered Arrays of Ge(Si) Quantum Dots Incorporated into Two-Dimensional Photonic Crystals

Semiconductors - Two different approaches to the integration of self-assembled Ge(Si) quantum dots into two-dimensional photonic crystals are considered. One approach includes the synthesis of an...     

Plasmon Enhancement of the Electric Field in Mid-Infrared Ge/Si Quantum-Dot Photodetectors with Different Thicknesses of the Active Region

Semiconductors - The spatial distribution of the electric field in Ge/Si photodetector heterostructures coated with a gold film containing a regular two-dimensional array of subwavelength apertures...     

Photovoltaic Ge/Si quantum dot detectors operating in the mid-wave atmospheric window (3-5 micrometers)

ABSTRACT: Ge/Si quantum dots fabricated by molecular-beam epitaxy at 500C are overgrown with Si at different temperatures Tcap, and effect of boron delta-doping of Si barriers on the mid-infrared photoresponse was investigated. The photocurrent maximum shifts from 2.3 to 3.9 micrometer with increasing Tcap from 300 to 750C. Within the sample set, we examined devices with different positions of the delta-doping layer with respect to the dot plane, different distances between the delta-doping layer and the dot plane d, and different doping densities pB. All detectors show pronounced photovoltaic behavior implying the presence of an internal inversion asymmetry due to the placing dopants in the barriers. The best performance was achieved for the device with Tcap=600C, pB=12x10^{11} cm^{-2}, and d=5 nm in a photovoltaic regime. At a sample temperature of 90K and no applied bias, a responsivity of 0.83 mA/W and detectivity of 8x10^{10} cmHz^{1/2}/W at lambda=3.4 micrometer were measured under normal incidence infrared radiation.     

Applicability of the six-band kp -model equations to semiconductor heterostructures

The problem of the applicability of the six-band kp -model to heterostructures with sharp boundaries is studied by calculating the energy spectrum of holes in the Ge/Si system with quantum dots. The boundary conditions which satisfy the conditions of particle flux conservation and the wave function continuity on the heterojunction are formulated at the level of differential equations and are characterized by a single parameter µ, which depends on the heterojunction properties. It is shown that a certain choice of µ leads to nonphysical interface states that fill the entire band gap. Conditions (range of µ) for the absence of such nonphysical states are determined by considering the simplest cases —a single heterojunction and a quantum well..