Biexcitons in Si

We observe a new peak in the photoluminescence spectrum of intrinsic Si which we attribute to the recombination of an electron-hole pair in a biexciton leaving behind a free exciton. A calculation of the emission line shape based on a simple model is found to be in good agreement with experiment. From this theoretical fit we deduce a binding energy of 1.2 meV and a ‘radius’ of 100 Å for the biexciton.     

Electron-hole liquid and excitonic molecules in quasi-two-dimensional SiGe layers of Si/SiGe/Si heterostructures

The electron-hole liquid (EHL) in SiGe layers of Si/Si_{1 − x} Ge _x /Si quantum-confinement heterostructures is discovered. It is composed of quasi-two-dimensional holes in the quantum well formed by the SiGe layer and quasi-three-dimensional electrons, which occupy a wider region of space centered on this layer. The densities of electrons and holes in the EHL are determined to be p ₀ ≈ 8.5 × 10¹¹ cm⁻² and n ₀ ≈ 4.8 × 10¹⁸ cm⁻³, respectively. It is demonstrated that the gas phase consists of excitons and excitonic molecules. The conditions on the band parameters of the structure under which the formation of the EHL of this kind and biexcitons is possible are formulated.     

Effective electron mass in high-mobility SiGe/Si/SiGe quantum wells

The effective mass m* of the electrons confined in high-mobility SiGe/Si/SiGe quantum wells has been measured by the analysis of the temperature dependence of the Shubnikov-de Haas oscillations. In the accessible range of electron densities, n _s , the effective mass has been found to grow with decreasing n _s , obeying the relation m*/m _b = n _s /(n _s ? n _c ), where m _b is the electron band mass and n _c ≈ 0.54 × 10¹¹ cm^?2. In samples with maximum mobilities ranging between 90 and 220 m²/(V s), the dependence of the effective mass on the electron density has been found to be identical suggesting that the effective mass is disorder-independent, at least in the most perfect samples.     

Layer Crystallization in PZT/LNO/Si Heterostructures

Physics of the Solid State - A Pb(Zr0.52Ti0.48)O3–LaNiO3–Si composition and LaNiO3 thin films are synthesized using chemical solution deposition and studied by transmission electron...     

Strain-induced anodization of SiGe/Si multiple layers to form high density SiGe/Si heterogeneous nanorods

SiGe/Si heterogeneous nanostructures are prepared by electrochemical anodization of SiGe/Si multiple layers grown by ultra-high vacuum chemical vapor deposition. Nanorods with densities up to ～2×10¹¹ cm^?2 have been observed with a relatively uniform distribution confirmed by scanning electron microscope images of both top and cross-sectional views. The samples show visible photoluminescence with multiple peaks and narrow widths which is related to the interference effect. Finally, a model is proposed to explain the role of strain during the anodization of SiGe/Si multiple layers.     

Phase transitions in nonequilibrium electron-hole systems of Si/SiGe/Si nanoheterostructures

The exciton condensation in a Si_1?x Ge _x solid solution layer of Si/Si_1?x Ge _x /Si heterostructures with the formation of electron-hole liquid has been investigated by low-temperature photoluminescence spectroscopy. In the temperature range above the critical temperature of the transition from an exciton gas to electron-hole liquid, a Mott transition from an exciton gas to electron-hole plasma has been found and investigated.     

Si/SiGe量子级联激光器研究进展

Si／SiGe量子级联激光器是一种新型的带内跃迁的红外光源，突破了Si基材料间接带隙特性对光跃迁的限制。Si/SiGe量子级联激光器的开发将为实现太赫兹有源器件的硅基集成产生深远影响。文章介绍了Si/SiGe量子级联激光器的工作原理，以及这类激光器在能带设计、材料生长和波导制作方面的最新进展。     

Free-standing Si/SiGe micro- and nano-objects

Free-standing SiGe/Si microtubes, microneedles, helical coils, bridges and submicron vertical rings have been fabricated from elastically strained SiGe/Si heterostructures grown by ultra-high vacuum chemical vapor deposition. Three-dimensional micro- and nano-objects have been formed by self-scrolling after electron beam lithography, reactive ion etching and wet selective etching. Vertical rings with very smooth sidewalls may have applications in hot embossing lithography as well as in microelectronics and micromechanics. By adjusting the SiGe/Si bilayer thickness or Ge concentration, the diameter of tube or ring could be decreased into the nanometer scale.     

Si/SiGe量子级联激光器研究进展

Si/SiGe量子级联激光器是一种新型的带内跃迁的红外光源,突破了Si基材料间接带隙特性对光跃迁的限制.Si/SiGe量子级联激光器的开发将为实现太赫兹有源器件的硅基集成产生深远影响.文章介绍了Si/SiGe量子级联激光器的工作原理,以及这类激光器在能带设计、材料生长和波导制作方面的最新进展.     

Simple Models of Lateral Heterostructures

Physics of the Solid State - General analytical expressions for densities of states of a lateral heterostructure, formed by the contact of two square semi-infinite lattices with single-band and...     

Infrared absorption in SiGe/Si multiple quantum wells

Infrared absorption has been used to investigate the subband structures in SiGe/Si quantum wells. The quantum wells are prepared using RRH/VLP-CVD and consist of 20 periods of and 60 periods of . The good periodical and interface sharpness of the SiGe/Si quantum wells have been shown by Auger Electron Spectroscopy (AES). The absorption peaks due to transitions between the hole subbands and the conduction band have been observed in infrared absorption spectra. The transverse photocurrent spectrum parallel to the growth plane have also shown absorption peaks due to transitions between the heavy and light hole band states and the conduction band states in quantum wells.     

Electric subbands in Si/SiGe strained layer superlattices

The subband structure for electrons in Si/SiGe strained layer superlattices along the (100) direction is calculated self-consistently including many-body effects in the local density approximation. The strain induced splitting of the six-fold degenerate conduction band results in different potential wells for different valleys. The charge distribution between the layers and valleys is calculated versus carrier concentration and conduction band offset for different strains. An estimate for the band offsets is obtained by comparison of experimental results with the calculations.     

Visible luminescence enhancement methods in SiGe/Si heterostructures

The possibility of increasing the photoluminescence signal of Si1?xGex/Si quantum wells in the visible spectral range due to a change in the conduction band structure and the interaction of many-body states with plasma oscillations of metal nanoparticles is studied. The sample band structure was controlled using a uniaxial strain of ～10?4. It is found that such an approach allows an increase in the emission intensity of biexcitons in the quantum well (x = 9%) by a factor of 2.4 at a temperature of 5 K. Metal nanoparticles deposited on the sample surface with a protective layer thickness of 20 nm allowed us to increase the luminescence intensity of quantum wells approximately by a factor of 2.7.     

Fractional Quantum Hall Effect in SiGe/Si/SiGe Quantum Wells in Weak Quantizing Magnetic Fields

We have experimentally studied the fractional quantum Hall effect in SiGe/Si/SiGe quantum wells in relatively weak magnetic fields, where the Coulomb interaction between electrons exceeds the cyclotron splitting by a factor of a few XX. Minima of the longitudinal resistance have been observed corresponding to the quantum Hall effect of composite fermions with quantum numbers p = 1, 2, 3, and 4. Minima with p = 3 disappear in magnetic fields below 7 T, which may be a consequence of the intersection or even merging of the quantum levels of the composite fermions with different orientations of the pseudo-spin, i.e., those belonging to different valleys. We have also observed minima of the longitudinal resistance at filling factors ν = 4/5 and 4/11, which may be due to the formation of the second generation of the composite fermions.     

Realization of silicon quantum wires based on Si/SiGe/Si heterostructure

We report on the successful fabrication of silicon quantum wires with SiO2 boundaries on SiGe/Si heterostructures by combining Si/SiGe/Si heteroepitaxy, selective chemical etching, and subsequent thermal oxidation. The observational result of scanning electron microscope is demonstrated. The present method provides a well-controllable way to fabricate silicon quantum wires.     

Electroluminescence from Si/SiGe quantum cascade emitters

Intersubband electroluminescence results are presented from Si/SiGe quantum cascade emitters at 3.2 THz and at temperatures up to 150 K. The effect of adding doping into the active quantum wells was studied in addition to reduced barrier widths from previous measurements. While the current through the sample is increased by the addition of doping, the emitted power is reduced through additional free carrier absorption and Coulombic scattering. Free electron laser measurements confirm the intersubband transitions in the quantum wells of the cascade devices and produce non-radiative lifetimes of 20 ps between 4 and 150 K.     

Nanomechanical characteristics of annealed Si/SiGe superlattices

In this study, the nanomechanical damage was investigated on the annealed Si/SiGe strained-layer superlattices (SLSs) deposited using an ultrahigh-vacuum chemical vapor deposition (UHVCVD). Nanoscratch, nanoindenter, atomic force microscopy (AFM), and transmission electron microscopy (TEM) techniques were used to determine the nanomechanical behavior of the SiGe films. With a constant force applied, greater hardness number and larger coefficients of friction (μ) were observed on the samples that had been annealed at 600 °C, suggesting that annealing of the Si/SiGe SLSs can induce greater shear resistance. AFM morphological studies of the Si/SiGe SLSs revealed that pile-up phenomena occurred on both sides of each scratch, with the formation of some pellets and microparticles. The Si/SiGe SLSs that had been subjected to annealing under various conditions exhibited significantly different features in their indentation results. Indeed, the TEM images reveal slight dislocation propagation in the microstructures. Thus, the hardness and elastic modulus can be increased slightly after annealing treatment because the existence of comparatively unstable microstructures. It is suggested that cracking phenomena dominate the damage cause of Si/SiGe SLSs.     

Impact of misfit dislocations on wavefront distortion in Si/SiGe/Si optical waveguides

Silicon-rich SiGe alloys represent a promising platform for the development of large-area single-mode optical waveguides to be integrated in silicon-based optical circuits. We find that SiGe layers epitaxially grown on Si successfully guide radiation with a 1.55 μm wavelength, but, beyond a critical core thickness, their optical properties are strongly affected by the clustering of misfit dislocations at the interface between Si and SiGe, leading to a significant perturbation of the local refractive index. Transmission electron microscopy and micro-Raman spectroscopy, together with finite-element simulations, provide a complete analysis of the impact of dislocations on optical propagation.     

氧化SiGe/Si多量子阱制备Si基SiGe弛豫衬底

SiGe弛豫衬底是制备高性能Si基SiGe光电子器件的基础平台。本文通过1050℃不同时间氧化SiGe/SiMQW材料,分析氧化过程中Ge组分、弛豫度的变化趋势,制备位错密度低、表面平整、弛豫度超过60%的Si基Si0.75Ge0.25缓冲层。