摘要:

Rapid solidification phenomena have been studied in amorphous germanium films on silicon substrates by means of real time reflectivity measurements performed during irradiation with nanosecond laser pulses. The influence of the thermal response of the film/substrate system has been investigated by comparing the behavior of films with thicknesses in the range of 30–180 nm. Two different solidification scenarios are observed depending on the ratio between film thickness(d)and the thermal diffusion length(l)of amorphous germanium (l≈80 nmfor 12 ns laser pulses). In the thinner films(d<l),reamorphization occurs upon solidification. Recalescence is observed in the thicker ones(d⩾l)when the melt depth induced is above of≈80 nm.Above this threshold, crystalline phases are nucleated upon solidification. The origin of this melt depth threshold is discussed in terms of the heat flow into the substrate, the supercooling prior to solidification, and the need of a minimum amount of initially solidified material. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366095

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a detailed study of molecular beam epitaxial growth of ZnS films on bare and arsenic-passivated vicinal Si(100) surfaces. This study elucidates the initiation of microtwinning and stacking-fault defects on double-stepped substrate surfaces. The study also sheds light on the function of arsenic passivation in reducing crystal defects in ZnS epitaxial layers. Three substrate surfaces, Si(100)2×1,Si(100):As2×1,and Si(100):As1×2,were used for the ZnS epitaxial growth studies. Adsorption experiments were performed to demonstrate the chemical passivation effect of an arsenic overlayer. Reflection high-energy electron diffraction was used to study growth modes and the epitaxial relationship of the ZnS layers to the substrates. Transmission electron microscopy was used to study the crystal-defect structures. Secondary ion mass spectroscopy was used to determine the chemical profiles of the heteroepitaxial interfaces of ZnS layers grown on arsenic-passivated surfaces. One of the main results demonstrated by this work is that thin ZnS films can be grown epitaxially with much better crystal quality on As-passivated Si surfaces than on bare Si surfaces. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366031

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The mixed Group V ternary alloyGaAs1−yPy(y<0.17)has been grown by metal organic vapor phase epitaxy and doped with oxygen using the oxygen precursor, diethylaluminum ethoxide[C2H5OAl(C2H5)2].Controlled oxygen doping was accomplished over the range of0<y<0.17.Deep level transient spectroscopy measurements reveal the presence of several oxygen-related deep levels. These levels, previously found in GaAs:O, vary with alloy composition over the investigated range. An additional deep level, most probably associated with the presence of misfit-related defects, has been identified. Photoluminescence performed on the oxygen-doped samples indicates that band edge emission is reduced and lower energy emission features are introduced over the wavelength range of 1000–1200 nm as a result of oxygen incorporation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366032

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Period expansion of Co/C and CoN/CN soft x-ray multilayers has been investigated by x-ray diffraction and Raman spectroscopy. Below the anneal temperature of 400 °C, the period expansion (< 12&percent;) of Co/C multilayers is mainly caused by the graphitization of the amorphous carbon layers. By 500 °C, the crystallization and agglomeration of Co layers induce an enormous period expansion (∼40&percent;). The period expansion of CoN/CN multilayers is only 4&percent; at 400 °C, which is much smaller than that of Co/C multilayers. The interface patterns of the CoN/CN multilayers still exist even if they were annealed at 700 °C. The Raman spectroscopy analyses indicate that the formation of thesp3bonding can be suppressed effectively by doping N atoms, and thus the period expansion is decreased considerably at annealing temperatures below 600 °C. The significant suppression of grain growth above 600 °C is believed to be attributed to the coexistence of hcp and fcc Co structures induced by interstitial N atoms, which cause the high-temperature period expansion decrease. The results also imply that the structural stability of Co/C soft x-ray multilayers can be significantly improved through doping N atoms.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366033

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The lateral oxidation rate of AlAs layers decreases dramatically for layers thinner than about 500 Å, because the activation energies for the rate constant of the reaction at the oxidation front increases by an amount inversely proportional to the layer thickness. We derive a model for the thickness dependence of the lateral oxidation rate of AlAs based on the surface energy of the curvature observed at the oxide tip. From the model, we show that the linear oxidation rate has anexp(−&thgr;0/&thgr;)dependence on the AlAs layer thickness&thgr;, and we can predict the slowing of oxidation when the AlAs layer is cladded with AlGaAs barriers. Also, we estimate the surface energy of the AlAs/oxide interface to be 50 eV/nm2. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366034

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The surface and interface structures of ZnTe epilayers grown by molecular beam epitaxy on GaSb (001) substrates under different conditions have been investigated by high resolution x-ray diffraction and grazing incidence scattering. Reciprocal space mapping around the symmetrical diffraction reciprocal point 004 and asymmetrical diffraction point 1¯1¯5 showed that the ZnTe epilayers, in the samples investigated, were fully strained to the substrate. The crystalline quality of the ZnTe epilayer grown on a substrate annealed in a Zn flux was very good, while evidence for an interfacial layer, of thickness varying from 2–20 nm, was found when the substrate was annealed in a Te flux prior to growth. This is attributed toGa2Te3formation at the interface. The interfacial layer roughens the interface and surface, and both crystal truncation rod measurements and grazing incidence x-ray reflectivity show the surface roughness to be about 4 nm. Such a rough surface and interface is also inferred from the broader distribution along the transverse direction in reciprocal space maps. A shorter lateral correlation length is found for the roughness of the sample containing the interfacial layer. The disappearance of interference fringes is attributed to nonuniformity of the interfacial layer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366035

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

B-doped Si(001) films, with concentrationsCBup to1.7×1022 cm−3,were grown by gas-source molecular-beam epitaxy fromSi2H6andB2H6atTs=500–800 °C.D2temperature-programed desorption (TPD) spectra were then used to determine B coverages&thgr;Bas a function ofCBandTs.In these measurements, as-deposited films were flash heated to desorb surface hydrogen, cooled, and exposed to atomic deuterium until saturation coverage. Strong B surface segregation was observed with surface-to-bulk B concentration ratios ranging up to 1200. TPD spectra exhibited&bgr;2and&bgr;1peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced peaks&bgr;2*and&bgr;1*.Increasing&thgr;Bincreased the area under&bgr;2*and&bgr;1*at the expense of&bgr;2and&bgr;1and decreased the total D coverage&thgr;D.The TPD results were used to determine the B segregation enthalpy,−0.53 eV,and to explain and model the effects of high B coverages on Si(001) growth kinetics. Film deposition ratesRincrease by⩾50&percent;with increasingCB>˜1×1019 cm−3atTs⩽550 °C,due primarily to increased H desorption rates from B-backbonded Si adatoms, and decrease by corresponding amounts atTs⩾600 °Cdue to decreased adsorption site densities. AtTs⩾700 °C,high B coverages also induce {113} facetting. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.366036

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The observed binding energy shift for silicon oxide films grown on crystalline silicon varies as a function of film thickness. The physical basis of this shift has previously been ascribed to a variety of initial state effects (Si–O ring size, strain, stoichiometry, and crystallinity), final state effects (a variety of screening mechanisms), and extrinsic effects (charging). By constructing a structurally homogeneous silicon oxide film on silicon, initial state effects have been minimized and the magnitude of final state stabilization as a function of film thickness has been directly measured. In addition, questions regarding the charging of thin silicon oxide films on silicon have been addressed. From these studies, it is concluded that initial state effects play a negligible role in the thickness-dependent binding energy shift. For the first∼30 Åof oxide film, the thickness-dependent binding energy shift can be attributed to final state effects in the form of image charge induced stabilization. Beyond about 30 Å, charging of the film occurs. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366037

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A semiconducting GaN thin film with the 001 plane parallel to the surface grown by organometallic vapor phase epitaxy method on (110) sapphire was studied using x-ray diffraction. The line profiles of the GaN thin film along the [001] direction can be quantitatively reproduced assuming a strained lattice at the interface. The deformation and growth faults were determined to be equal and each is 0.2&percent;. Least-squares refinement on 42 independent peaks, after correcting for the first-order thermal diffuse scattering, gives the values of the Debye–Waller factor for Ga(B11=0.28,B33=0.26)and N(B11=0.38,B33=0.26)atoms. The wurtzite positional parameterufor this GaN thin film was found to be 0.3730, 1&percent; smaller than that in a strain-free single crystal(u=0.377),most probably resulting from the strain effects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366038

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Polycrystalline bccTixW1−xlayers with mixed 011 and 002 texture were grown on oxidized Si(001) substrates at 600 °C by ultrahigh-vacuum (UHV) magnetron sputter deposition from W andTi0.33W0.67targets using both pure Ar and Xe discharges. Ti concentrations in the 100-nm-thick layers were 0, 6, and 33 at. &percent; depending on target composition and sputtering gas. Al overlayers, 190 nm, thick with strong 111 preferred orientation, were then deposited in Ar at 100 °C with and without breaking vacuum. Changes in bilayer sheet resistanceRswere monitored as a function of timetaand temperatureTaduring subsequent UHV annealing. Thermal ramping of Al/W andAl/Ti0.06W0.94bilayers at 3 °Cmin−1resulted in large (>fourfold) increases inRsatTa≃550 °C,whereasRsin theAl/Ti0.33W0.67bilayers did not exhibit a similar increase until ≃610 °C. Area-averaged and local interfacial reactions and microstructural changes were also followed as a function of annealing conditions. The combined results indicate that Al/W andAl/Ti0.06W0.94bilayer reactions proceed along a very similar pathway in which monoclinicWAl4forms first as a discontinuous interfacial phase followed by the nucleation of bccWAl12whose growth is limited by the rate of W diffusion, with an activation energy of 2.7 eV, into Al. In contrast, the W diffusion rate during the early stages ofAl/Ti0.33W0.67annealing is significantly higher allowing the formation of a continuousWAl4interfacial blocking layer which increases the overall activation energyEa,still limited by W diffusion, to 3.4 eV and strongly inhibits further reaction. We attribute observed increases inWAl4nucleation and growth rates in interfacialAl/Ti0.33W0.67to a “vacancy wind” effect associated with the very rapid(Ea=1.7eV) diffusion of Ti into Al. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366039

出版商:AIP    

年代:1997

数据来源: AIP