MBE生长InGaAs/GaAs(001)多层矩阵式量子点

用分子束外延(MBE)设备以Stranski-Krastanov(S-K)生长模式,通过间歇式源中断方式外延生长了多个周期垂直堆垛的InGaAs量子点,首次获得大小及密度可调的In0.43Ga0.57As/GaAs(001)矩阵式量子点DWELL结构。样品外延结构大致为500nm的GaAs、多个周期循环堆垛InGaAs量子点和60ML的GaAs隔离层等。生长过程中用反射式高能电子衍射仪(RHEED)实时监控,样品经退火后使用扫描隧道显微镜(STM)进行表面形貌的表征。     

InAs/GaAs nanostructures grown on patterned Si(001) by molecular beam epitaxy

The potential benefit from the combination of the optoelectronic and electronic functionality of III-V semiconductors with silicon technology is one of the most desired outcomes to date. Here we have systematically investigated the optical properties of InAs quantum structure embedded in GaAs grown on patterned sub-micron and nanosize holes on Si(001). III-V material tends to accumulate in the patterned sub-micron holes and a material depletion region is observed around holes when GaAs/InAs/GaAs is deposited directly on patterned Si(001). By use of a 60?nm SiO(2) layer and patterning sub-micron and nanosize holes through the oxide layer to the substrate, we demonstrate that high optical quality InAs nanostructures, both quantum dots and quantum wells, formed by a two-monolayer InAs layer embedded in GaAs can be epitaxially grown on Si(001). We also report the power-dependent and temperature-dependent photoluminescence spectra of these structures. The results show that hole diameter (sub-micron versus nanosize) has a strong effect on the structural and optical properties of GaAs/InAs/GaAs nanostructures.     

Methylthiolate adsorbed on as-rich GaAs (001) surface

The adsorption of the methylthiolate (MT) on the as-rich GaAs (001) surface has been studied by using density functional theory (DFT) calculations with a three-dimensional periodic boundary condition. A complete characterization of structures and binding energies of the system consisting of MT and As-rich GaAs (001) surface is obtained. It is found that the most reactive binding site is related to empty Ga dangling bonds located at the threefold-coordinated second-layer Ga atom. Moreover, electronic properties of these structures are also calculated to study the bonding characteristics of S–Ga and S–As bonding, which show that the covalent bonding of the former is stronger than that of the latter. The analysis for this shortest chain binding is helpful to realize the electrical passivation and chemical protection of GaAs surfaces.     

Electrical Properties of ZnSe Epilayers on GaAs(001)

The electrical properties (conductivity, mobility and concentration of majority carriers, and energy spectrum of deep-level defects) of ZnSe layers grown on GaAs(001) by molecular-beam epitaxy were investigated. The results were used to assess the effects of growth rate, ZnSe surface reconstruction, and Ga indiffusion from the substrate on the parameters of the epilayers.     

Dynamics of dysprosium silicide nanostructures on Si(001) and (111) surfaces

The growth and coarsening dynamics of dysprosium silicide nanostructures are observed in real-time using photoelectron emission microscopy. The annealing of a thin Dy film to temperatures in the range of 700–1050 °C results in the formation of epitaxial rectangular silicide islands and nanowires on Si(001) and triangular and hexagonal silicide islands on Si(111). During continuous annealing, individual islands are observed to coarsen via Ostwald ripening at different rates as a consequence of local variations in the size and relative location of the surrounding islands on the surface. A subsequent deposition of Dy onto the Si(001) surface at 1050 °C leads to the growth of the preexisting islands and to the formation of silicide nanowires at temperatures above where nanowire growth typically occurs. Immediately after the deposition is terminated, the nanowires begin to decay from the ends, apparently transferring atoms to the more stable rectangular islands. On Si(111), a low continuous flux of Dy at 1050 °C leads to the growth of kinked and jagged island structures, which ultimately form into nearly equilateral triangular shapes.     

Photoluminescence studies of InAs/GaAs quantum dots covered by InGaAs layers

Photoluminescence (PL), PL excitation (PLE), and time-resolved PL were used to study effects of InGaAs layers on the optical properties of InAs/GaAs quantum dots (QDs). A rich fine structure in the excited states of confined excitons (up to n = 4 quantum states) was observed, providing useful information to study the quantum states in the InAs/GaAs QDs. A significant redshift of the PL peak energy for the QDs covered by InGaAs layers was observed, attributing to the decrease of the QD strain and the lowing of the quantum confinement.     

Effect of thin intermediate-layer of InAs quantum dots on the physical properties of InSb films grown on (001) GaAs

In this study the formation of a semiconducting InSb layer, preceded by the growth of an intermediate layer of InAs quantum dots, is attempted on (001) GaAs substrate. From the analysis of atomic-force-microscopy and transmission-electron-microscopy images together with Raman spectra of the InSb films, it is found that there exists a particular layer-thickness of ~ 0.5 μm above which the structural and transport qualities of the film are considerably enhanced. The resultant 2.60-μm-thick InSb layer, grown at the substrate temperature of 400 °C and under the Sb flux of 1.5 × 10^− 6 Torr, shows the electron mobility as high as 67,890 cm²/Vs.     

Time-resolved photoluminescence of type-II Ga(As)Sb/GaAs quantum dots embedded in an InGaAs quantum well

Optical properties and carrier dynamics in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) are reported. A large blueshift of the photoluminescence (PL) peak is observed with increased excitation densities. This blueshift is due to the Coulomb interaction between physically separated electrons and holes characteristic of the type-II band alignment, along with a band-filling effect of electrons in the QW. Low-temperature (4?K) time-resolved PL measurements show a decay time of [Formula: see text]?ns from the transition between Ga(As)Sb QDs and InGaAs QW which is longer than that of the transition between Ga(As)Sb QDs and GaAs two-dimensional electron gas ([Formula: see text]?ns).     

Structure and thermodynamic stability of GaAs(001) surfaces

The surface energies for a set of structural models for the reconstructions occuring on GaAs(001) were calculated with the first principles pseudopotential method and the local density approximation. On the basis of these calculations we are able to rule out the single-dimer-vacancy model for the 2 × 4 surface as a possible equilibrium structure. In the As-rich limit we find the c(4 × 4) As addimer model to be energetically favorable. As the Ga chemical potential increases the surface is predicted to transform into the β2(2 × 4) structure having two As dimers in the top layer and a third As dimer in the third layer. The (2 × 4) structure, with two As dimers above a complete layer of Ga is found to be stable in a very narrow range. The β(4 × 2) structure and the model recently proposed by Skala et al. for the (4 × 2) reconstruction were determined to be energetically unfavorable. In the Ga-rich limit the lowest energy structure we have obtained is the β2(4 × 2) model.     

High extractive single-photon emissions from InGaAs quantum dots on a GaAs pyramid-like multifaceted structure

This work investigates the single-photon emissions from self-assembled InGaAs quantum dots that are grown on an apex plane of a GaAs pyramid-like multifaceted structure. The number of QDs on a multifaceted structure is estimated by scanning electron microscopy. Single-exciton emissions from individual quantum dots are examined by micro-photoluminescence and by making photon correlation measurements. This experiment demonstrates the improvement of the single-photon extraction efficiency as quantum dots are grown on a reduced apex plane of a multifaceted structure.     

Self-organization of quantum dots in multilayer InAs/GaAs and InGaAs/GaAs structures by submonolayer migration-stimulated epitaxy

Multilayer structures of InGaAs/GaAs quantum dots fabricated by submonolayer migrationstimulated epitaxy have been studied experimentally by scanning tunneling microscopy and results are presented. These results clearly show that in multilayer structures, ordering of nanoobjects into rows occurs in InAs and InGaAs heteroepitaxial layers. Pis#x2019;ma Zh. Tekh. Fiz. 23, 80–84 (November 26, 1997)     

Photoluminescence intermittency of InGaAs/GaAs quantum dots confined in a planar microcavity

Photoluminescence intermittency, or "blinking", was observed in semiconductor InGaAs/GaAs quantum dots (QDs) inside a planar microcavity. Most of the blinking QDs were found around defect sites such as dislocation lines naturally formed in the GaAs barrier layers, and the carrier traps responsible for blinking had an excitation threshold of approximately 1.53 eV. The blinking properties of epitaxial QDs and colloidal nanocrystal QDs were also compared by performing laser intensity dependent measurements and statistics of the "on" and "off" time distributions.     

Planar Hall Effect in Epitaxial Fe Layers on GaAs(001) and GaAs(113)A Substrates

For ferromagnetic layers with in-plane magnetic fields, the longitudinal and transverse resistivities probe the magnetization orientation and its reversal via a spin-orbit-related resistance anisotropy. In the planar Hall effect, we found new contributions in Fe films on GaAs(001) and GaAs(113)A substrates, which cannot be understood within the conventionally used model of the resistance anisotropy. To understand its origin, we adopted a method to determine the orientation of the magnetization from magnetoresistance data. As a result, we were able to identify a symmetric fourfold and a twofold saturated asymmetric in-plane Hall effect for the Fe/GaAs(001) and Fe/GaAs(113)A systems, respectively. Since these new contributions almost perfectly compensate the planar Hall effect based on the resistance anisotropy, we argue about an intrinsic origin of the planar Hall effect in terms of scattering at spin textures within the Fe films.     

MBE方法在GaAs(001)衬底上外延生长GaSb膜

利用分子束外延方法(MBE)在GaAs(001)衬底上外延生长了GaSb薄膜,利用高分辨透射电子显微镜(HRTEM)、原子力显微镜(AFM)、Hall效应(HallEffect)和低温光荧光谱(LTPL)等手段对薄膜的晶体质量、电学性能和光学质量进行了研究。发现直接生长的GaSb膜表面平整,空穴迁移率较高。引入GaSb/AlSb超晶格可有效阻断进入GaSb外延层的穿通位错,对应的PL谱强度增强,材料的光学质量变好。     

Nanopatterning of Si(001) for bottom-up fabrication of nanostructures

The epitaxial growth of Si on Si(001) under conditions at which the (2?×?n) superstructure is forming has been investigated by scanning tunneling microscopy and Monte Carlo simulations. Our experiments reveal a periodic change of the surface morphology with the surface coverage of Si. A regular (2?×?n) stripe pattern is observed at coverages of 0.7-0.9 monolayers that periodically alternates with less dense surface structures at lower Si surface coverages. The MC simulations show that the growth of Si is affected by step-edge barriers, which favors the formation of a rather uniform two-dimensional framework-like configuration. Subsequent deposition of Ge onto the (2?×?n) stripe pattern yields a dense array of small Ge nanostructures.     

Mechanism of photoluminescence quenching of InGaAs/GaAs quantum dots resulting from nanoprobe indentation

The low-temperature (10 K) photoluminescence (PL) of self-assembled InGaAs/GaAs quantum dots (QDs) was measured under the elastic indentation of a flat cylindrical nanoprobe that generates localized strain fields around itself. As the indentation force increases, the intensity of the PL fine peak from a single QD firstly increases, followed by a decrease, and is finally quenched. The observed force at which a PL peak disappears, i.e., the quenching force varies from QD to QD. This variation is ascribed to the diversely distributed strain fields in and around each QD and therefore can be related to the QD location with respect to the nanoprobe center. In order to clarify the mechanism of PL quenching, a numerical simulation of the strain distribution is carried out by a 3-dimensional finite element method. The modification of the energy band structure resulting from strain is then calculated based on the deformation potential theory. We concluded that the PL quenching observed experimentally can be attributed to the electron-repulsion resulting from the strain-induced potential gradient. Based on this mechanism, an indentation-induced shift of the electron-potential in bulk GaAs, at which the PL from QDs is quenched, was deduced to be 43.5-133.5 meV.     

InP(001)基衬底上自组织生长InAs量子点(线)的光学性质研究

在InP(001)基衬底上用分子柬外延方法生长InAs纳米结构材料，通过衬底的旋转与否及混合生长模式，得到了两种InAs量子点和量子线，并研究了量子点、线的光学性质，结果表明，两种方式都可生长出较强发光的量子点(线)；由量子点排列构成的量子线的光致发光光谱呈现出多峰结构，分析和理论计算表明这是InAs量子线上各量子点在垂直方向上不同高度分布和非连续性而造成的。     

Nucleation of Ge quantum dots on the C-alloyed Si(001) surface

Carbon pre-deposition onto the bare Si(001) surface has been shown to alter the (2×1) surface structure by formation of c(4×4) reconstructed domains containing a high C-concentration. Here we studied by ultra-high vacuum scanning tunneling microscopy the effect of this restructured surface on the initial stages of Ge nucleation by molecular beam epitaxy. Ge is found to form three-dimensional (3D) islands already at sub-monolayer coverage, resulting in a Volmer–Weber growth mode. Strain effects repel Ge adatoms from the C-rich domains, leading to enhanced Ge island formation on the C-free surface regions in between the c(4×4) areas. At a low growth temperature of 350°C, very small three-dimensional islands (3–5 nm in diameter, height 3–4 ML) with a density of nearly 1×10¹² cm⁻² are obtained for only 0.5 ML of Ge. At higher substrate temperatures of approximately 500°C this three-dimensional growth mode is less pronounced, but still evident. The initially nucleated three-dimensional islands define the positions of the larger quantum dots at higher Ge coverage, that exhibit enhanced photoluminescence (PL) properties.