摘要:

Reflection x-ray pole figure analysis techniques were used to study the heteroepitaxial relationships of the cobalt germanideCoGe2to GaAs(100). The alloy films were grown using the partially ionized beam deposition technique, in which low energyGe+ions are employed to alter the heteroepitaxial orientation of theCoGe2deposits. TheCoGe2[001](100)∥GaAs[100](001)orientation, which has the smallest lattice mismatch, was found to occur for depositions performed at a substrate temperature around 280 °C and with∼1200 eVGe+ions. Lowering the substrate temperature or reducing theGe+ion energy leads toCoGe2(100)orientation domination withCoGe2[100](010)∥GaAs[100](001)andCoGe2[100](001)∥GaAs[100](001).Substrate temperature alone was seen to produce only theCoGe2(100)orientation. ForCoGe2(001)films, additional energy was required fromGe+ions in the evaporant stream. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365323

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The initial stages of molecular beam epitaxy of GaSb on highly mismatched GaAs(001) substrates were investigated. Transmission electron microscopy was used to analyze the defect structure in GaSb islands and at their interfaces with GaAs(001) at different stages of growth. Based on experimental observations, we propose that the semiperiodic net of 90° misfit dislocations at the GaSb/GaAs(001) interface nucleate homogeneously at the leading edges of advancing {111} planes. After nucleation, they glide inwards along the interface plane to reach their equilibrium position. Threading dislocations in GaSb layers were directly correlated with the misfit dislocation net. We demonstrate that there are no threading defects in GaSb islands when their interfaces consist solely of 90° misfit dislocations, and that threading dislocations in the GaSb epilayer are all associated with minority 60° misfit dislocations nucleated in growing islands. The number of threading dislocations per unit area of the GaSb film is found to be independent of GaSb coverage, indicating that island coalescence does not substantially increase the number of 60° dislocations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365324

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Generation of extra facets on ridge-type triangles with (001)-, (110)-, and (201)-related equivalent slopes on GaAs (111) A substrates and stripes running in the [1¯10], [110], and [100] directions on (001) substrates during molecular beam epitaxy of GaAs/AlGaAs multilayers was investigated. By investigating local variation in layer thickness in the regions adjacent to extra (114)A, (110), and (1¯1¯1¯)B facets common to the (111)A and (001) patterned substrates and extra facets specific to the respective substrates and growth rates of the facets relative to the growth rate on the substrate plane, the orientation-dependent Ga surface diffusion length,&lgr;Ga,was elucidated as&lgr;Ga(001)≈&lgr;Ga(1¯1¯3¯)B<{&lgr;Ga(1¯1¯1 ¯)B,&lgr;Ga(3¯3¯1¯)B,&lgr;Ga(013),&lgr;Ga(113)A}<&lgr;Ga(159)≈&lgr;Ga(114)A≈&lgr;Ga(111)A<&lgr;Ga(110).That is,&lgr;Gaincreases in the order of the (001), (1¯1¯1¯)B-related, (111)A-related, and (110) surfaces.

ISSN:0021-8979    

DOI:10.1063/1.365548

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Intrinsic andn-type microcrystalline silicon thin films were deposited on intrinsic hydrogenated amorphous silicon by the layer-by-layer technique. The growth of the samples has been analyzedin situby kinetic ellipsometry, spectroscopic ellipsometry, and dark conductivity measurements. Thisin situanalysis has shown that the process of deposition can be divided into four phases: incubation, nucleation, growth, and steady state. Moreover we have found striking differences between the growth of undoped andn-type samples in both the kinetics of the formation of crystallites and the zone where the nucleation of crystallites takes place. According to ourin situconductivity measurements, the percolation threshold occurs for a crystalline volume fraction higher than 20&percent; in both cases. Moreover, we can produce very thin (6 nm) and highly conductive(&sgr;d≈0.2 S cm−1)n-type microcrystalline silicon films on intrinsic amorphous silicon. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365325

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

GaSe, a layered semiconductor, may be grown on the Si(111) surface by molecular beam epitaxy. The crystalline quality is relatively good, in the sense that the MeV4Heion minimum channeling yield(∼30&percent;)is as low as that of state-of-the-art bulk material, and the interface is atomically abrupt. The initial film deposits are epitaxial islands, and subsequent growth is in the Frank–van der Merwe mode. With the islands already relaxed at the nucleation stage and coalescing to essentially uniform coverage with the first monolayer of deposition, GaSe on Si(111) provides an example of van der Waals epitaxy. However, it is difficult to understand how epitaxy (crystallographic alignment with the substrate) can occur in such a case, where the film is incommensurate starting from the initial nuclei. A mechanism for alignment of the islands is proposed: they are aligned with the silicon substrate through the influence of dangling bonds at their perimeter, being “quasi-commensurate ” by virtue of their small lateral size. Although discommensurate regions are created as the islands grow laterally, there is simply no change in their orientation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365326

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structures and defects are studied in arsenic-ion-implantedGaAs(As+–GaAs)films annealed at temperatures higher than 600 °C by using transmission electron microscopy, deep level transient spectroscopy, temperature-dependent conductance, and photoluminescence. The estimated concentration of arsenic precipitates in films decreases from∼4×1016 cm−3to∼6×1015 cm−3and the corresponding size increases from∼3to∼10 nmas the annealing temperature increases from 600 to 800 °C. A defect with an energy level at about 0.3 eV from the band edge is found and its concentration increases with the increasing annealing temperatures. The electrical transport of free carriers is replaced by hopping conduction, through the defect band at about 0.26 eV below conduction band, when the film is annealed at temperature 800 °C. It indicates that during high-temperature annealing the defect of the arsenic and gallium vacancies due to the diffusion of As and Ga atoms is the dominant factor to change its electrical and structural properties. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365327

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The microstructural and magnetic properties of amorphous Co/Ti multilayer films and their variation with temperature are investigated by transmission electron microscopy (TEM) analysis and thermomagnetic measurements. Thermomagnetic curves showed two peaks at about 400 and 520 °C. The evolution of the structure monitored in the hot stage of the TEM was found to be consistent with the magnetic changes. The first peak of the saturation magnetizationMsat 400 °C was associated with the transformation from amorphous ferromagnetism to paramagnetism due to the amorphous Co existing in the film.Msbegan to increase corresponding to the crystallization point of the ferromagnetic Co phase, which decreased with increasing amounts of Co in the film.Msreached its maximum at 520 °C and then decreased because the phase transition occurred at a temperature greater than 520 °C and approached completion at 650 °C. The amorphous phase and crystalline phase formation and phase transition during annealing were observed in Co/Ti multilayer thin films and successfully explained the thermomagnetic properties of the film. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365328

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Molecular stacking structures in epitaxial crystals of oxotitanium and oxovanadium phthalocyanines (TiOPc and VOPc) prepared by physical vapor deposition (PVD) and molecular beam epitaxy (MBE), respectively, onto the (001) face of a KBr substrate were investigated by means of x-ray and electron diffraction studies. In thin epitaxial film of VOPc deposited by MBE at a substrate temperature of 20 °C, the flat-lying molecules oriented in the(3×3)commensurate square lattice(a=1.40 nm)were alternately stacked with body-centered head-to-head anda/4-slipped face-to-face dimeric bilayers. The crystal structure determined was the triclinic space groupP1¯witha=b=1.40,c=1.06 nm,&agr;=109.2,&bgr;=133.9,&ggr;=90.0°,Z=2.When TiOPc was thickly deposited by PVD at a substrate temperature of 200 °C, islandlike crystals epitaxially grew in a truncated pyramidal morphology and assumed the same orientation. In the pyramidal crystals the thick molecular layer stacking separate from the KBr surface was relaxed and had a square lattice with a shorter constant(a=1.33 nm).The three-dimensional stacking structure explained the observed grain boundary formation and asymmetric pyramidal morphology. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365329

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Interfaces between conducting polymer polypyrrole (PP) and transparent conductive materials such as indium tin oxide (ITO) andSnO2were investigated by x-ray photoemission spectroscopy (XPS). XPS lines ofIn 3d5/2,3/2andSn 3d5/2,3/2were observed in the XPS spectra of electrochemically reduced PP film sides of PP/ITO andPP/SnO2,respectively. The results indicate that electrochemical diffusion of substrate materials into conducting polymer films takes place by applying negative voltage to the substrate. The energy positions of the3dlines of the diffused In and Sn which are close to those of the metal oxides support the proposition that the diffused species are metal oxide ions. In the electrochemically diffused PP/ITO andPP/SnO2interfaces, XPS spectra of substrate sides exhibitIn 3dandSn 3dlines associated with satellite peaks, which indicates magnetic splitting of3dlevels or electron transfer typed shake-up. This indicates that electrochemical diffusion affects the substrate electronically. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365353

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The segregation of B fromSi1−xGexquantum wells grown using molecular beam epitaxy on Si(100) and Si(110) was investigated using secondary ion mass spectrometry. When a 3 nm B doping slab(n=1019/cm3)was placed in the center of a 6 nmSi1−xGexquantum well, the B profiles had two distinct exponential decay lengths,&Dgr;SiGe, the Ge-controlled B decay length and&Dgr;Si, the B decay length normally measured in Si.&Dgr;SiGewas the same for Si(100) and Si(110) and independent of Ge concentration in the well for0.1⩽x⩽0.5.As the Ge concentration was increased in the well, the location of the transition point, from&Dgr;SiGeto&Dgr;Si,which was always found far outside of the SiGe quantum well, increased in distance from the center of the well.

ISSN:0021-8979    

DOI:10.1063/1.365359

出版商:AIP    

年代:1997

数据来源: AIP