Growth of high-crystallinity uniform GaAs nanowire arrays by molecular beam epitaxy

The self-catalyzed growth of Ga As nanowires(NWs) on silicon(Si) is an effective way to achieve integration between group III–V elements and Si. High-crystallinity uniform Ga As NW arrays were grown by solid-source molecular beam epitaxy(MBE). In this paper, we describe systematic experiments which indicate that the substrate treatment is crucial to the highly crystalline and uniform growth of one-dimensional nanomaterials. The influence of natural oxidation time on the crystallinity and uniformity of Ga As NW arrays was investigated and is discussed in detail. The Ga As NW crystallinity and uniformity are maximized after 20 days of natural oxidation time. This work provides a new solution for producing high-crystallinity uniform III–V nanowire arrays on wafer-scale Si substrates. The highly crystalline uniform NW arrays are expected to be useful for NW-based optical interconnects and Si platform optoelectronic devices.     

GaAs(111)表面硅烯、锗烯的几何及电子性质研究

基于密度泛函理论的第一性原理计算方法, 系统研究了硅烯、锗烯在GaAs(111) 表面的几何及电子结构. 研究发现, 硅烯、锗烯均可在As-中断和Ga-中断的GaAs(111) 表面稳定存在, 并呈现蜂窝状六角几何构型. 形成能计算结果证明了其实验制备的可行性. 同时发现硅烯、锗烯与GaAs表面存在共价键作用, 这破坏了其Dirac电子性质. 进一步探索了利用氢插层恢复硅烯、锗烯Dirac电子性质的方法. 发现该方法可使As-中断面上硅烯、锗烯的Dirac电子性质得到很好恢复, 而在Ga-中断面上的效果不够理想. 此外, 基于原子轨道成键和杂化理论揭示了GaAs表面硅烯、锗烯能带变化的物理机理. 研究结果为硅烯、锗烯在半导体基底上的制备及应用奠定了理论基础.     

Surface structure of GaAs(211)

The atomic structures of the two inequivalent (211) surfaces of GaAs have been investigated by LEED. Both surfaces, prepared by etching and heat-cleaning or ion-sputtering and annealing, are unstable and develop large (110) facets which exhibit the atomic geometry of the (110) GaAs surface. These facets entirely cover the surface. Three sets of facets, making 30°, 30° and 54° angles with the (211) plane, are detected on one surface. Only two sets, making 30° angles with the (211) plane, are detected on the other. The reasons for this difference are not understood at this time. The LEED study of Si(211) and Ge(211) shows that the Si surface is flat whereas the Ge surface exhibits reconstructed (311) facets. The structural difference between the (211) surfaces of GaAs and Ge and the facetting of the compound are invoked to explain the problems encountered in the MBE growth of GaAs on Ge(211).     

Orientation-patterned templates GaAs/Ge/GaAs for nonlinear optical devices. I. Molecular beam epitaxy

GaAs/Ge/GaAs heterostructures in which the GaAs layer lattice on Ge is rotated at a right angle to the substrate plane are grown by molecular-beam epitaxy (MBE). Such heterostructures are grown in different epitaxial setups for GaAs and for Ge with wafer transfer through air tor the first time. It is proposed to use surfactants (Bi, Sb) to control GaAs layer nucleation on Ge.     

Molecular beam epitaxy growth of GaAs on an offcut Ge substrate

Molecular beam epitaxy growth of GaAs on an offcut Ge (100) substrate has been systemically investigated. A high quality GaAs/Ge interface and GaAs film on Ge have been achieved. High temperature annealing before GaAs deposition is found to be indispensable to avoid anti-phase domains. The quality of the GaAs film is found to strongly depend on the GaAs/Ge interface and the beginning of GaAs deposition. The reason why both high temperature annealing and GaAs growth temperature can affect epitaxial GaAs film quality is discussed. High quality In_0.17Ga_0.83As/GaAs strained quantum wells have also been achieved on a Ge substrate. Samples show flat surface morphology and narrow photoluminescence line width compared with the same structure sample grown on a GaAs substrate. These results indicate a large application potential for III--V compound semiconductor optoelectronic devices on Ge substrates.     

有源层掺杂剂对Ga1-xAlxAs/GaAs双异质结发光管特性的影响

本文研究了由液相外延技术生长的GaAIAs/GaAs双异质结材料制成的发光管,有源层掺杂剂对器件特性的影响结果表明,器件结构和器件制作工艺相同的GaAIAs/GaAs发光管,有源层掺Si可获得较大的光输出功率,而频响特性<15MHz,波长在8700Å以上;对有源层掺Ge器件,光输出功率低于掺Si器件,而频响特性则>15MHz,波长可控制在8200Å~8500Å.深能级测量表明二者有不同的深能级位置,对掺Si(氧沾污)器件,Ec-ET≈0.29eV,而掺Ge器件ET-Ev≈0.42eV.两种掺杂剂对有源层暗缺陷的影响尚无明显区别.     

GaAs/Ge/GaAs Heterostructures for Use in Nonlinear Optics

GaAs/Ge/GaAs heterostructures with sublattice reversed GaAs on Ge epilayers grown via molecular beam epitaxy (MBE) for periodic domain inverted structures are presented. For the first time, such structures are grown in separate MBE machines for GaAs and Ge with atmospheric wafer transfer. The high quality of the heterostructures is confirmed via X-ray diffraction and photoluminescence. It is proposed that the surfactants (Bi, Sb) be used to control the nucleation of GaAs epilayers on a Ge epilayer.     

Structure of heteroepitaxial GaAs on Si

The current interest in GaAs grown on nonpolar substrates such as Si has been stimulated by the potential technological advantages of this system. Although the two major obstacles impeding the progress of heteroepitaxial growth of GaAs on Si (100) substrates, the large lattice mismatch and the formation of antiphase boundaries, have recently been overcome, the understanding of the microstructural growth process is still not satisfactory. We are presenting new x-ray scattering results which indicate that thin GaAs films are compressed in the film plane at room temperature, while thicker films are under tensil stress, the cross-over region being at about 1000Å. In addition, we show that the GaAs lattice is translationally incommensurate with the Si substrate and that the in-plane [001] axes are misaligned by 3–5°. Thermal expansion measurements of the out-of-plane lattice parameters of the film and substrate indicate that the GaAs in-plane thermal expansion follows from the anharmonicity of the substrate.     

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.     

AFM morphological characterization and Raman study of germanium grown on (111)GaAs

In this communication we report on the growth of Ge heterolayers on (100), (111)Ga and (111)As surfaces of GaAs substrates. Arsenic can play a role as both dopant and surfactant, changing the growth mechanism for the Ge/GaAs growth on (001) oriented substrates. The use of substrates oriented in different directions can change the growth mode and produce different results, since surface polarity can induce different growth modes: we have compared the results on (111) substrates with respect to the non-polar surface case.The growth behavior on (001), (111)Ga and (111)As substrates is discussed. The layer morphology was investigated by Atomic Force Microscopy and Raman spectroscopy has been carried out as a function of the sample thickness.     

Studies of the promising material CoSi2 on GaAs substrates

The thermal stability of CoSi₂ thin films on GaAs substrates has been studied using a variety of techniques. The CoSi₂ thin films were formed by depositing Co(500 Å) and Si(1800 Å) layers on GaAs substrates by electron-beam evaporation followed by annealing processes, where the Si inter-layer was used as a diffusion/reaction barrier at the interface. The resistivity of CoSi₂ thin films formed is about 30 cm. The Schottky barrier height of CoSi₂/n-GaAs is 0.76 eV and the ideality factor is 1.14 after annealing at 750° C for 30 min. The CoSi₂/GaAs interface is determined to be thermally stable and the thin film morphologically uniform on GaAs after 900° C/30 s anneal. The CoSi₂ thin films fulfill the requirements in GaAs self-aligned gate technology.     

优质GaAs/Si和AlGaAs/Si材料的MOCVD生长研究

用自制常压MOCVD装置,在Si衬底上生长GaAs和AlGaAs外延层,在高温去除Si衬底表面氧化膜之后,采用两步法,即低温生长过渡层,再提高温度生长外延层。得到了表面镜面光亮的优质GaAs和AlGaAs外延层。X射线双晶衍射仪测试GaAs外延层,其回摆曲线半峰宽是200孤秒,GaAs和AlGaAs外延层在77K温度下,PL谱半峰宽分别是17meV和24meV。     

GaAs/AlAs super-flat interfaces in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells grown on (4 1 1)A GaAs substrates by MBE

Effectively atomically flat GaAs/AlAs interfaces over a macroscopic area (“super-flat interfaces”) have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells (QWs) grown on (4 1 1)A GaAs substrates by molecular beam epitaxy (MBE). A single and very sharp photoluminescence (PL) peak was observed at 4.2 K from each GaAs/AlAs or GaAs/(GaAs) (AlAs) QW grown on (4 1 1)A GaAs substrate. The full-width at half-maximum (FWHM) of a PL peak for GaAs/AlAs QW with a well width ( ) of 4.2 nm was 4.7 meV and that for GaAs/(GaAs) (AlAs) QW with a smaller well width of 2.8 nm (3.9 nm) was 7.6 meV (4.6 meV), which are as narrow as that for an individual splitted peak for conventional GaAs/AlAs QWs grown on (1 0 0) GaAs substrates with growth interruption. Furthermore, only one sharp peak was observed for each GaAs/(GaAs) (AlAs) QW on the (4 1 1)A GaAs substrate over the whole area of the wafer (7 7 mm ), in contrast with two- or three-splitted peaks reported for each GaAs/AlAs QW grown on the (1 0 0) GaAs substrate with growth interruption. These results indicate that GaAs/AlAs super-flat interfaces have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) QWs grown on the (4 1 1)A GaAs substrates.     

GaAs衬底上生长的GaInP_2外延单晶薄膜的杂质污染研究

各种外延技术已被用来在ＧａＡｓ衬底上生长ＧａｘＩｎ１－ｘＰ外延单晶薄膜（ＧａＩｎＰ２／ＧａＡｓ）．很多文献认为,在ＧａＩｎＰ２／ＧａＡｓ生长过程中会被Ｃ杂质污染．我们用高灵敏的ＣＡＭＥＣＡＩＭＳ４Ｆ型二次离子质谱仪直接测量的结果表明,污染ＧａＩｎＰ２／ＧａＡｓ的微量杂质是Ｓｉ,而不是Ｃ．由ＧａＩｎＰ２／ＧａＡｓ在１．１７ｅＶ附近的光致发光峰的峰值随激发强度的变化形状表明了它应属于施主－受主对复合发光．进一步分析表明,施主为处在Ｇａ格位上的Ｓｉ杂质（ＳｉＧａ）,受主为Ｇａ空位（ＶＧａ）．     

高温处理工艺对低压MOCVD外延GaAs/Ge太阳电池的影响

采用自制的低压金属有机化学汽相淀积LP-MOCVD设备,在Ge衬底(100)面向(111)偏9°外延生长出GaAs电池结构,对电池材料进行了X射线衍射分析另外,对由此材料制成的太阳电池进行了性能测试,测试结果表明,Ge衬底的高温处理工艺对GaAs/Ge太阳电池的电流电压特性有一定的影响试验表明,在600～700℃之间高温处理效果较好。     

Self-consistent tight-binding total energy calculations: Application to GaAs/Si and ZnSe/GaAs (100) interfaces

Self-consistent tight-binding total energy calculations are performed for various models of GaAs/Si and ZnSe/GaAs (100) interfaces. A graded GaAs/Si interface with the first monolayer on substrate having 1 As atom per 3 Si atoms followed by a second monolayer with 3 Ga atoms per 1 Si atom and continued with 2 bulk-like As and Ga monolayers is found to be structurally more stable than other interfaces. The instability of the abrupt interface is driven by elastic rather than electrostatic forces. Similar results are obtained for the ZnSe/GaAs (100) interface. The graded interface with Ga atoms exchanged against Zn atoms is found to be energetically most stable. Strong macroscopic electric fields are found in the surface and interface regions for both the GaAs/Si and ZnSe/GaAs interfaces.     

Electron diffraction on GaAs nanowhiskers grown on Si(100) and Si(111) substrates by molecular-beam epitaxy

The crystal structure of GaAs nanowhiskers grown by molecular-beam epitaxy on Si(111) and Si(100) substrates is investigated using reflection high-energy electron diffraction (RHEED). It is revealed that, in both cases, the electron diffraction images contain a combination (superposition) of systems of reflections characteristic of the hexagonal (wurtzite and/or 4H polytype) and cubic (sphalerite) phases of the GaAs compound. The growth on the Si(111) substrates leads to the formation of nanowhiskers with hexagonal (wurtzite and/or 4H polytype) and cubic (sphalerite) structures with one and two orientations, respectively. In the case of the Si(100) substrates, the grown array contains GaAs nanowhiskers that have a cubic structure with five different orientations and a hexagonal structure with eight orientations in the (110) planes of the substrate. The formation of the two-phase crystal structure in nanowhiskers is explained by the wurtzite—sphalerite phase transitions and/or twinning of crystallites.     

Pulsewidth-dependence of nonlinear energy deposition and redistribution in Si, GaAs and Ge during 1 μm picosecond irradiation

We have used 1 μm pulses ranging in duration from 4–260 ps to measure the pulsewidth dependence of the nonlinear absorption, melting threshold, and resolidification morphologies of Si, GaAs, and Ge. With these materials, we have been able to quantify a variety of nonlinear absorption processes with a single excitation wavelength. We find that the fluence required to melt Si and GaAs is roughly proportional to the square root of the pulsewidth while that required for Ge is nearly pulsewidth independent. A crystalline-to-amorphous transition is observed in Si for pulses less than 10 ps and in GaAs for all pulsewidths, but no such transition is observed in Ge. These observations are shown to be consistent with the various energy deposition and redistribution mechanisms present in each material. Finally, we have used the active nonlinearities in Si and GaAs to construct optical limiters designed to protect sensitive optical components from intense 1 μm radiation.     

GaAs/SiO_2超晶格的制备和Raman光谱研究

我们采用射频磁控溅射方法在 p- Si衬底上成功地制备出四周期的非晶 Ga As/Si O2超晶格 ,并取得其高分辨率电镜像。以 80 0℃快速退火方法使超晶格中非晶的 Ga As层局部晶化 ,利用 Raman散射谱研究了其结构变化。     

Electronic states of (2 × 1) and (1 × 1) (111) surfaces of Ge,Si, diamond,GaAs and Ge on Si

The “dangling-bond” surface state dispersion curves, E(k), have been calculated for the (2 × 1) and (1× 1) (111) surfaces of Ge, Si, and diamond, for (1 × 1) GaAs, and for (2 × 1) Ge on Si. The calculations employ the sp³s1 empirical tight-binding model of Vogl et al. and the atomic relaxation of Feder et al. The surface state band gaps are in good agreement with optical-absorption and electron-energy-loss measurements for Ge and Si. For the assumed epitaxial geometry, Ge on Si is predicted to shift the dangling-bond states downward by ≈0.1 to 0.4 eV.