用低能电子衍射研究GaAs(110)表面的弛豫

用低能电子衍射研究了GaAs(110)表面的弛豫。发现当理论与实验之间符合得最好时,得到的结构是,保持表面上As—Ga键长不变用一个27.32°±0.24°的旋转角(ω),使As原子向外移动0.10±0.02?,Ga原子向内移动0.55±0.02?,而从Ga到第二层时空间为d₂=1.45±0.01?,从第二层Ga到第三层的空间为d₃=2.01±0.01?。对此结构As的背键长l_As=2.43±0.01?(收缩0.56％),而Ga的背键长l_Ga=2.253±0.004?(收缩8.0％)。 关键词：     

金属铝在半导体表面的吸附

本文采用集团模型,用自洽的EHT方法计算金属Al在Si(111)和GaAs(110)面上吸附的稳定的几何构型和电子态,结果表明,Al在Si(111)面的三度开位上的离子吸附比顶位的共价吸附更稳定,态密度与实验符合也更好,Al吸附在GaAs(110)面上,将取代表面Ga原子,形成AlAs,此时GaAs(110)面将恢复到不弛豫的理想位置。 关键词：     

Cl在GaAs(110)面上的吸附

本文主要研究Cl是吸附在GaAs(110)理想表面还是弛豫表面,是与表面正离子成键还是与表面负离子成键。计算采用集团模型和密度自洽的EHT方法。结果表明Cl只能吸附在弛豫的GaAs(110)面上,与表面As原子成键。在这个位置上吸附Cl的态密度与实验符合较好。 关键词：     

碱金属在GaAs(110)表面上的吸附

本文讨论Li,Na,K,Cs在GaAs(110)表面上的吸附,考虑理想表面和弛豫表面两种情况。计算采用集团模型,用电荷自洽的ExtendedHucheltheory(缩写为EHT)方法进行。结果表明,吸附后表面原子趋向于理想位置,碱金属原子位于垂直于表面沿[001]方向横跨表面Ga原子的对称平面上。碱金属吸附后的费密能级在价带顶以上约0.7eV处,是由表面Ga原子与碱金属原子间的相互作用决定的。而在价带中碱金属原子主要与表面As原子成键。 关键词：     

GaAs(110)面的紧束缚计算

本文研究了GaAs(110)弛豫表面的紧束缚计算,采用了有饱和的slab(薄片)模型,来模拟半无限大的晶体。通常的slab模型有两个表面,本模型与其不同之处在于用类As和类Ga原子来饱和伸向体内的悬挂键,使之只保留一个表面,从而大大降低久期矩阵的阶数。从计算的表面定域态密度表明,采用五层的有饱和的Slab模型,就可以得到较好的结果。 关键词：     

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     

Si,GaAs(111)表面弛豫效应

本文将赝原子轨道的线性组合方法应用于计算半导体表面电子结构。除了赝势的形状因子以外,不引入任何可调参量。用这方法计算了Si和GaAs(111)理想表面和弛豫表面的电子态和波函数。Si的结果与Appelbaum和Hamann的自洽计算结果在表面能级位置和表面电荷分布两方面都符合得比较好。计算结果表明,当表面Si或Ga原子向内位移时,表面能级向上移动;表面As原子向外位移时,表面能级向下移动。同时,表面态波函数的性质往往也发生较大的变化。 关键词：     

GaAs中过渡金属深杂质能级的计算

本文采用41个原子的原子族模型来模拟晶体,用电荷-组态自洽(SCCC)的EHMO方法和在边界上用"类Ga"和"类As"原子来饱和悬挂键,计算了中性过渡金属原子Cr、Mn、Fe、Co、Ni在半导体GaAs中的深杂质态,所得杂质能级在带隙中的位置与实验结果相符。     

用HREELS研究氢在GaAs和InP的(111),(111)表面上的吸附

氢在GaAs和InP表面上的吸附可以用高分辨率电子能量损失谱(HREELS)来探测。Ga—H,As—H,In—H和P—H键的伸缩振动各自对应于不同的能量损失。但是As—H振动极容易和Ga—H振动追加声子损失相混淆,只有从损失峰的相对强度比较上来区别。实验得到吸附的氢与表面原子的成键情况取决于表面的原子结构及电子分布。对于GaAs(111)面,低暴露量时只形成Ga—H键,而高暴露量时还可以形成As—H键。而InP(111)表面由于是经过磷气氛退火处理的,在低暴露量下In—H与P—H键均可形成。InP(Ⅲ)面上只看到P—H损失峰,说明这个表面是完全以P原子结尾的。在(Ⅲ)面上出现小面的情形,则表面Ⅲ族和Ⅴ族原子均可同氢成键。 关键词：     

用HREELS研究氢在GaAs和InP的(111),()表面上的吸附

氢在GaAs和InP表面上的吸附可以用高分辨率电子能量损失谱(HREELS)来探测。Ga—H,As—H,In—H和P—H键的伸缩振动各自对应于不同的能量损失。但是As—H振动极容易和Ga—H振动追加声子损失相混淆,只有从损失峰的相对强度比较上来区别。实验得到吸附的氢与表面原子的成键情况取决于表面的原子结构及电子分布。对于GaAs(111)面,低暴露量时只形成Ga—H键,而高暴露量时还可以形成As—H键。而InP(111)表面由于是经过磷气氛退火处理的,在低暴露量下In—H与P—H键均可形成。InP(Ⅲ)面上只看到P—H损失峰,说明这个表面是完全以P原子结尾的。在(Ⅲ)面上出现小面的情形,则表面Ⅲ族和Ⅴ族原子均可同氢成键。     

Cluster model approach for electronic structure of Si and Ge(111) and GaAs(110) surfaces

For the purpose of exploring how realistic a cluster model can be for semiconductor surfaces, extended Huckel theory calculations are performed on clusters modeling Si and Ge(111) and GaAs(110) surfaces as prototypes. Boundary conditions of the clusters are devised to be reduced. The ideal, relaxed, and reconstructed Si and Ge(111) surfaces are dealt with. Hydrogen chemisorbed (111) clusters of Si and Ge are also investigated as prototypes of chemisorption systems. Some comparison of the results with finite slab calculations and experiments is presented. The cluster-size dependence of the calculated energy levels, local densities of states, and charge distributions is examined for Si and Ge(111) clusters. It is found that a 45-atom cluster which has seven layers along the [111] direction is large enough to identify basic surface states and study the hydrogen chemisorption on Si and Ge(111) surfaces. Also, it is presented that surface states on the clean Si and Ge(111) clusters exist independent of relaxation. Further, the calculation for the relaxed GaAs(110) cluster gives the empty and filled dangling-orbital surface states comparable to experimental data and results of finite slab calculations. The cluster approach is concluded to be a highly useful and economical one for semiconductor surface problems.     

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).     

THE ADSORPTION OF Ge ON GaAS(ll0)

In the present work, the chemisorption of Ge on GaAs(1lO) was studied by a cluster model using the charge self-consistent extended H ückel method (EHT) and the results thus obtained were compared with those derived from the experiments. It was shown from the calculation that after chemisorption, the substrate tends to relax back to the ideal unrelaxed state, after cleavage. The tilted angle of the As-Ga bond was reduced from the well khown 27° to 10°.The gap states which were driven into both the valence band and the conduction band due to relaxation will-be introduced into the gap after chemisorption. From the calculation of the total energy of the cluster, it was found that the Ge atom could bind to both Ga and As atoms although the binding of the latter was somewhat stronger. The gap states were derived from the p states of Ge and the s and p states of Ga and As atoms. The states will serve as donors and acceptors for p and n type materials respectively . From a comparison with the previous results concerning studies of group Ⅲ and Ⅴ metals on GaAs(110) surface, it seems that the change of surface relaxation after chemisorption might be the origin of gap states and the cause for Fermi level pinningr. The explanation was first put forward by Chen et al . from their experimental studies . The present calculation also gives the core shifts of Ga(3d) and As(3d) of the clean relaxation surfaces with respect to that of the bulk as well as the core shifts of Ga(3d) and As(3d) after the chemisorption of Ge atom. A chemisorption induced state which is attributed to a precursor state for a heterojunction interface state is also obtained at a binding energy near 7eV which is in fairly good agreement with the experimental result.     

Kinetics of the total cluster perimeter in thin film nucleation on solid surfaces

The time evolution of the total perimeter of clusters growing on a surface has been described on the basis of the JMAK (Johnson-Mehl-Avrami-Kolmogoroff) statistical theory. A general formula, which can be easily extended to any space dimension, is obtained. When particular nucleation functions and the cluster growth law are considered the kinetics of the perimeter can be explicitly calculated and moreover, it can be expressed as a function of the covered surface. Experimental data on the efficiency of a Cu/CuO_x model catalyst, towards imide formation, have been satisfactorily described by the model. Moreover, the growth of Ag on a GaAs(110) surface studied via photoelectron spectroscopy has been qualitatively explained by the proposed model. In the model case of cylindrical clusters the knowledge of the evolution of the total perimeter allows the entire area of the film to be evaluated.     

Alkali metal adsorption on the gallium arsenide surface: A change in the work function

A change in the work function when Cs atoms are adsorbed on the GaAs(100) surface and K, Rb, and Cs atoms are adsorbed on the GaAs(110) surface is calculated with a simple model. The model includes both dipole-dipole interaction of adatoms and broadening of their quasi-levels due to exchange effects. The results of calculation are in good agreement with experimental data.     

A CLUSTER MODEL METHOD AND ITS APPLICATIONS TO CHEMISORPTIONS ON SEMICONDUCTOR SURFACES

In the present paper the cluster model and charge self-consistent method are used to study the chemisorpti on Si(lll1), Ge(111), and GaAs(110) surfaces. The parameters in the calculations are selected to fit the respective bulk energy bands of Si, Ge, and GaAs. Some general rules of chemisorpti on Si(ll1) and Ge(ll1) are investigated and speculated. The three-fold hollow site geometry is favorable for group iii metals on Si(lll), whereas the one-fold top site is more stable for group vii elements, the reason being probably one of the favorable charge distribution. However, the situation for chemisorpti on Ge(ll1) is somewhat different. The adsorptions of group iii and v elements on GaAs(110) are also considered. The possible chemisorption geometries and the related electronic states for these systems are calculated and discussed.     

Dependence of the GaAs (110) surface electronic state dispersion curves on the surface relaxation angle

The surface state dispersion curves E($\text{k}$) of the dangling bond states near the fundamental band gap, C₃ and A₅, are computed for both the established θ?27° model and the recently proposed θ?7° model of the (110) surface relaxation of GaAs, where θ is the surface bond rotation angle. The two models produce surface state dispersion curves that are similar to one another and to the data.     

A virtual intersubband spin–flip spin–orbit coupling induced spin relaxation in GaAs (110) quantum wells

A spin relaxation mechanism is proposed based on a second-order spin–flip intersubband spin–orbit coupling together with the spin-conserving scattering. The corresponding spin relaxation time is calculated via the Fermi golden rule. It is shown that this mechanism is important in symmetric GaAs (110) quantum wells with high impurity density. The dependencies of the spin relaxation time on electron density, temperature and well width are studied with the underlying physics analyzed.