The oxidation of the GaAs (110) surface

It is demonstrated that, contrary to previous proposals, Ga surface atoms are already involved in the oxidation process for the lowest observable oxygen coverages (0.01 monolayer). A similar involvement of As atoms could not be readily ascertained experimentally, although it is to be expected from energetic considerations. An oxidation model consisting of multiple bridge bonds to both Ga and As surface atoms is proposed, which is consistent with diverse experimental data for the GaAs(110) surface.     

The surface geometry of GaAs(110)

Results of a fully dynamical low-energy electron diffraction calculation show that the GaAs(110) surface reconstructs with a top-layer tilt-angle of 27° ≤ ω ≤ 31°. The smaller tilt angle 7° ≤ ω ≤ 10° reported earlier is outside the error limits of the analysis and can be clearly ruled out. The results are independent of which R-factor or which set of existing experimental data is used. Lateral shifts larger than 0.1 Å for the surface atoms are necessary to obtain acceptable agreement with the measured intensity spectra.     

Optical detection of surface states in GaAs(110) and GaP(110)

We present results on the optical detection of surface states in GaAs(110)and GaP(110)by the method of the fractional change of external reflectivity. Optical transitions are observed at ～3.1 eV m GaAs(110) and ～3.4 eV in GaP. A comparison with existing theories suggests a rotational relaxation model for the surface, with partial relaxation for GaAs(110) and full relaxation for GaP(110).     

Many-body calculations for the relaxed (110) surface of GaAs

Quantum Monte Carlo methods are a stochastic approach to directly tackle the manybody problem in solids. They have proven to describe virutually exactly the ground state of correlated bulk systems, like the homogeneous electron gas or solids of C, Ge, Si and GaAs. Especially Variational quantum Monte Carlo calculations using nonlocal ab initio pseudopotentials offer a way to study systematically many-body effects at solid surfaces, safely founded on the variational principle “the lower the energy, the better the wave function”. Here we report on first attempts for the relaxed (110) surface of GaAs, serving as a prototype of semiconductor surfaces. A finite layer geometry is chosen as the boundary condition of the multidimensional stochastic integration scheme. The exact many-body Hamiltonian is cast in a form allowing for rapid evaluation. New parameters in the correlated trial wave function increase the variational freedom necessary to take into account the influence of the surface. Their physical meaning and their statistical significance are discussed in detail. Presented at the VIII-th Symposium on Surface Physics, Třešt’ Castle, Czech Republic, June 28 – July 2, 1999. This work was supported by the Deutsche Forschungsgemeinschaft under Grant No. Scha 360/17-1. Our calculations were performed on the Cray-T3E at the Zentralinstitut für Angewandte Mathematik, Forschungszentrum Jülich, and on the Cray-T3E at the Konrad-Zuse-Zentrum für Informationstechnik, Berlin.     

Oxygen adsorption and the surface electronic structure of GaAs (110)

The surface electronic structure of cleaved GaAs (110) is found to be very sensitive to small amounts of adsorbed oxygen. For example, adsorbing oxygen on only a few percent of the surface Ga or As atomic sites can produce changes of a factor of two in the surface electronic structure. Thus, long range effects must be involved, and these are associated with rearrangement of the surface atoms.     

Surface states and metal overlayers on the (110) surface of GaAs

We have found new surface states related to Al overlayers on the (110) surface of GaAs. These states play a prominent role in the determination of the electronic structure for metal-semiconductor interfaces. The results are consistent with conjectures of Rowe, Christman and Margaritondo based upon recent experimental results for metal overlayers on semiconductor surfaces.     

The surface geometry of GaAs(110): A response

A brief survey of the various surface structure analyses for GaAs(110) is presented. The interplay between studies based on low-energy-electron diffraction (LEED), ion channeling, ion scattering, photoemission and isochromat spectroscopy leads to a structure in which a relaxation within the top layer (characterized by a perpendicular displacement of the As and Ga species by $\text{Δ}{}_{\mathrm{1,\; \perp }}\text{= 0.69±0.05}\text{A}\text{?}$ with the As species relaxing outward by $\text{0.21±0.05}\text{A}\text{?}$ and the Ga species inward by $\text{0.48±0.05}\text{A}\text{?}$) is accompanied by a uniform relaxation of the top layer by $\text{0.05±0.1}\text{A}\text{?}$ toward the substrate and a perpendicular displacement in the second layer in the opposite sense by $\text{0.06±0.1}\text{A}\text{?}$. The displacements of the top-layer Ga and As species parallel to the surface remain controversial. LEED and medium-energy ion-scattering analysis favor bond-length-conserving rotated top-layer structures (i.e., large $\text{(Δd}{}_{\mathrm{|}}\text{～ 0.3}\text{A}\text{?}\text{)}$ displacements parallel to the surface) whereas high-energy ion-channeling and isochromat spectroscopy experiments favor small displacements $\text{(Δd}{}_{\mathrm{|}}\text{? 0.1}\text{A}\text{?}\text{)}$ parallel to the surface.     

True atomic resolution imaging of surface structure and surface charge on the GaAs(110)

We demonstrated a novel method to detect the van der Waals and the electrostatic force interactions simultaneously on an atomic scale, which is based on frequency modulation detection method. For the first time, the surface structure and the surface charge at atomic-scale point defects on the GaAs(110) surface have been simultaneously resolved with true atomic resolution under ultra-high vacuum condition. From the bias voltage dependence of the image contrast, we can verify that the sign of the atomically resolved surface charge at the point defect was positive.     

Xe原子吸附对GaAs(110)表面重构的影响

基于第一性原理的自洽场密度泛函理论(DFT)和广义梯度近似(GGA),利用缀加平面波加局域轨道(APW+lo)近似方法，建立了五层层晶超原胞模型，模拟了GaAs(110)表面结构和单个Xe原子在其表面的吸附.利用牛顿动力学方法，对GaAs(110)表面原子构形的弛豫和Xe原子在GaAs(110)表面的吸附进行了计算.从三种不同的初始构形出发，即Xe原子分别在Ga原子的顶位，As原子的顶位以及桥位，都发现Xe原子位于桥位时体系能量最低.由此，认为Xe原子在GaAs(110)表面的吸附位置在桥位，并且发现吸附Xe原子后GaAs(110)表面有趋向于理想表面的趋势，表面重构现象趋于消失，表面原子间键长有一定的恢复,这与理论预言相符合. 关键词： 密度泛函理论 表面结构 APW 表面原子吸附     

Electronic states near the band gap for the GaAs(110) surface

The recent theoretical controversy regarding empty surface states at the GaAs cleavage plane is examined by the exact solution of several tight binding models applied to a semi-infinite crystal. We correlate the existence of an empty surface gap state with the anion p/cation p character of this state. This work isolates the specific properties of a Hamiltonian for GaAs which yield band gap states on a relaxed surface and clarifies the essential differences among current theoretical treatments.     

Constant final state measurements of surface core-level binding energy shifts: InP(110) and GaAs(110)

The surface core-level binding energy shifts have been obtained for the In 4d and the P2p core-levels on the InP(110) surface. In agreement with previous studies of core-level shifts on the cleavage face of III–V semiconductors, the anion and cation shifts are of almost equal magnitude and are of opposite polarity (−0.31 and +0.30 eV respectively). The results are compared with a similar investigation of the GaAs(110) surface and discussed in terms of a recent calculation of surface core-level shifts for the (110) cleavage face of III–V semiconductors.