The initial growth of Au on GaAs(001)-c(4 × 4)

The metal growth when depositing a monolayer (ML) of Au at 200° C on MBE-grown surfaces of GaAs(001)-c(4 × 4) was studied by AES and RHEED. The surface interaction can be characterized to proceed in two stages depending on the surface coverage of Au. At a coverage of less than 0.3 ML the gold atoms are mainly dispersed on the surface with a small in depth diffusion. Above 0.4 ML there is a rapid intermixing and a tendency of arsenic accumulation to the surface.     

Ferromagnetism of MnAs studied by heteroepitaxial films on GaAs(001)

Thin epitaxial films of MnAs--promising candidates for the spin injection into semiconductors--are well known to undergo simultaneously a first-order structural and magnetic phase transition at 10-40 degrees C. The evolution of stress and magnetization of MnAs/GaAs(001), both measured quantitatively with our cantilever beam magnetometer at the coexistence region of alpha-MnAs and beta-MnAs, reveal an orthorhombically distorted unit cell of the ferromagnetic phase, which provides important clues on the origin of ferromagnetism in MnAs.     

Variable-temperature micromagnetic study of epitaxially grown MnAs films on GaAs(001)

We present variable-temperature magnetic force microscopy (VT-MFM) studies of epitaxially grown MnAs layers on GaAs(001). In MnAs, a structural and magnetic phase transition occurs at T_c40 °C from the hexagonal, ferromagnetic -phase below T_c to the orthorhombic, paramagnetic -phase above T_c. In the investigated MnAs-GaAs system, both phases coexist over a temperature range of 30 °C below T_c due to the involved strain. Using MFM we are able to distinguish between the ferromagnetic and the paramagnetic phases by measuring topographic and magnetic contrast of the same sample area. For VT-MFM studies, we have employed a temperature stage that allows heating and cooling in a controlled atmosphere with small thermal drift (for this system, the temperature was varied from below 0 °C to above 45 °C). The ratio of the ferromagnetic to the paramagnetic phases shows a temperature hysteresis, i.e. the ratio is dependent on whether the sample was heated or cooled to reach the measurement temperature. Detailed studies of the domains and their arrangements over the hysteretic temperature cycle are shown and compared. Mainly three different domain types are found that are dominant in their respective temperature ranges. PACS 68.37.Rt; 68.35.Rh; 75.70.-i     

Preparation and characterization of epitaxial Fe(001) thin films on GaAs(001)-based LED for spin injection

We report on the successful fabrication and characterization of ferromagnetic Fe/Tb multilayer contacts with perpendicular magnetic anisotropy (PMA) on the clean As-terminated surface of a GaAs(001)-based light-emitting diode (LED) structure. PMA was inferred from magnetometry and ⁵⁷Fe conversion electron Mössbauer spectroscopy. Such contacts are a potential candidate for optical detection of electron spin injection from the remanent magnetic state into the semiconductor.     

Island formation in Ge films on GaAs(1 1 0)

The early stages of GaAs (1 1 0)/Ge heterojunction formation at room temperature have been investigated by Auger spectroscopy. Comparison between the experimental results and the predictions of simple deposition models indicates that the growth of the Ge film proceeds by island formation. A uniform overlayer starts to develop only in films thicker than 10 Å. Evidence is also found for As diffusion through the Ge film.     

Subsurface dimerization in III-V semiconductor (001) surfaces

We present the atomic structure of the c(8 x 2) reconstructions of InSb-, InAs-, and GaAs-(001) surfaces as determined by surface x-ray diffraction using direct methods. Contrary to common belief, group III dimers are not prominent on the surface, instead subsurface dimerization of group III atoms takes place in the second bilayer, accompanied by a major rearrangement of the surface atoms above the dimers to form linear arrays. By varying the occupancies of four surface sites the (001)-c(8 x 2) reconstructions of III-V semiconductors can be described in a unified model.     

Kinetics in surface reconstructions on GaAs(001)

We have successfully controlled the surface structures of GaAs(001) by changing incident As-molecular species. Under As4 fluxes, the c(4 x 4) reconstruction with Ga-As dimers [c(4 x 4)alpha structure] is obtained, but the formation of three As-As dimer structures [c(4 x 4)beta structure] is kinetically limited. On the other hand, the structure change from the (2 x 4), through c(4 x 4)alpha, to c(4 x 4)beta phases is observed under As2 fluxes. We found that the c(4 x 4)alpha structure is energetically metastable and provides a kinetic pathway for the structure change between the (2 x 4) and c(4 x 4)beta phases under As2 fluxes.     

GaAs(001)衬底上分子束外延生长InNSb单晶薄膜

利用射频氮等离子辅助分子束外延(RF-MBE)技术在GaAs(001)衬底上生长稀氮 InNSb半导体薄膜,并通过原子力显微镜(AFM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和拉曼散射光谱等测量手段对样品的微结构和N组分等进行了表征.结果显示样品有较好的晶体质量,N组分可高达0.84%(XRD的结果).本文还对样品的输运性质进行了表征,结果显示样品在室温下具有较低的载流子浓度和较高的迁移率.另外,初步研究表明在InSb中掺入N可导致其室温磁阻明显下降. 关键词： 分子束外延 稀氮半导体 X射线衍射 拉曼光谱     

Magnetic properties of thermally deposited Fe/GaAs(100) thin films

Thin (50–200 Å) films of iron have been prepared on (100) gallium arsenide substrates by thermal evaporation at a deposition rate of 3–30 Å/s and a pressure of ～10^?5 torr. Dependences of the saturation magnetization, cubic and uniaxial planar anisotropy constants, and the ferromagnetic resonance linewidth on the film thickness were studied by ferromagnetic resonance at 9.8 GHz. It has been found that the parameters of thermally deposited Fe/GaAs (001) films are comparable to those achieved with molecular-beam epitaxy.     

Immobilization of avidin on (001) GaAs surface

To reliably immobilize different biomoieties on surfaces of III-V semiconductors is one of the most critical issues in the development of biodetector devices based on the optical/electronic properties of these materials. Herein we demonstrate the successful immobilization of avidin, a robust and well-studied protein, on a (001) GaAs surface. The immobilization was investigated via specific binding to biotin, which was connected to the GaAs surface through commercially available long- or short-chain amino group terminated alkanethiols (HS(CH₂)₁₁NH₂ or HS(CH₂)₂NH₂), or through a biotinylated thiol synthesized in our laboratory. The immobilization performance was evaluated by photoluminescence and fluorescence microscopy measurements. We found that the biotinylated thiol mixed with a diluent thiol provides the highest avidin immobilization efficiency. PACS 81.05.Ea; 82.65.+r; 87.14.Ee     

Chemisorption of Au on Si（001） surface

The chemisorption of one monolayer of Au atoms on an ideal Si(001) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption system of a Au atom on different sites are calculated. It is found that the most stable position is A site (top site) for the adsorbed Au atoms above the Si(001) surface. It is possible for the adsorbed Au atoms to sit below the Si(001) surface at the B_1 site(bridge site), resulting in a Au－Si mixed layer. This is in agreement with the experiment results. The layer projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated.