摘要:

Molecular‐beam epitaxy InAsySb1−ylayers were grown at temperatures ranging from 295 to 470 °C across the full composition range. Transmission electron microscopy and transmission electron diffraction (TED) examinations showed that for layers grown at and below 400 °C with nominal compositions 0.4<y<0.8, separation into two phases occurred resulting in a series of alternating plates approximately parallel to the layer surface. TED showed that the cubic lattices of the two phases were tetragonally distorted and their compositions were deduced to be typically InAs0.38Sb0.62and InAs0.72Sb0.28. The plates were larger and more regular along the [1¯10] direction than the [110] direction. As the growth temperature increased from 295 to 400 °C, for layers of nominal composition InAs0.5Sb0.5, the plate length increased from 0.1 to 2.0 &mgr;m and the plate thickness from 10 to 50 nm. Crystallographic defects were present in the layers and their occurrence was different in the phase‐separated and non‐phase‐separated layers. The plates formed spontaneously at the growing surface and were stable during subsequent annealing at 350 and 370 °C. It is suggested that they arise due to the presence of a miscibility gap at these growth temperatures. We have termed these spontaneously grown plate structures ‘‘natural’’ strained layer superlattices.

ISSN:0021-8979    

DOI:10.1063/1.353440

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two‐dimensional doping sheets (‘‘&dgr; doping’’) are integral parts of many novel semiconductor device concepts. Deep submicron design rules require junction depths significantly below 100 nm. This level of control is difficult to achieve with ion implantation. We discuss the application of thermal, coevaporative doping with Sb and elemental B during Si molecular beam epitaxy at growth temperatures below ≊300 °C to this problem. We show that it is possible to create structures with very high doping levels, yet with very sharp doping transitions. Delta‐doping spikes with a full width at half maximum of <2.7 nm and <4.0 nm have been obtained by secondary‐ion mass spectrometry for Sb and B, respectively, with corresponding up‐slopes of 2.5 and 0.94 nm/decade. Homogeneously doped films show full activation up toNSb≊6×1020cm−3andNB≳1×1021cm−3. Mobilities agree with bulk values at corresponding concentrations. Mesa‐isolatedpnjunctions exhibit ideality factors of 1.05.

ISSN:0021-8979    

DOI:10.1063/1.353441

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

350‐nm‐wavelength laser ablation of ceramic SiC targets has been used to deposit SiC films on fused silica and R‐cut sapphire at substrate temperatures from 300 to 1150 °C. The films deposited above 800 °C show (111) and (222) x‐ray‐diffraction bands from crystal planes parallel to the substrate. The bandwidths decrease and the integrated intensities increase with deposition temperature. The crystallite dimension for the highest‐temperature films is in the order of 50 nm. The diffraction peaks are absent for the films deposited at the lower temperatures. Analysis of optical transmission spectra of the high‐temperature films shows a lowest‐energy gap near 2.2 eV which is the value for cubic SiC. The low‐temperature films show smaller and variable gaps. The room‐temperature resistivities of the former are low, from 0.02 to 0.1 &OHgr; cm whereas the latter are insulating. Film thicknesses and deposition rates ranging from 0.2 to over 0.6 A˚/pulse are obtained from the spectra and by monitoring of the interference oscillations in the infrared emission through the film during deposition.

ISSN:0021-8979    

DOI:10.1063/1.353442

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

High‐quality, uniform, Si/NiSi2/Si(100) structures were demonstrated by a combination of molecular‐beam epitaxy and postgrowth, high‐temperature annealing. A Si template technique ensures the epitaxial orientation of the Si overlayer. The unusual inverse Volmer–Weber mode observed during the growth of Si on NiSi2(100) is shown to be a result of interface and surface energetics. The evolution of the interface morphology of the double‐heteroepitaxial structures is discussed in terms of thermodynamics.

ISSN:0021-8979    

DOI:10.1063/1.353443

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on atomically clean (111)Si at low temperatures have been studied by both conventional and high‐resolution transmission electron microscopy, Auger electron spectroscopy, and x‐ray diffraction. A 10‐nm‐thick yttrium thin film, deposited onto (111)Si at room temperature, was found to completely intermix with Si to form an 11‐nm‐thick amorphous interlayer. Crystalline Y5Si3and Si were observed to nucleate first within the amorphous interlayer in samples annealed at temperatures lower than 200 °C. Epitaxial YSi2−xwas found to be the only phase formed at the interface of amorphous interlayer and crystalline Si in samples annealed at temperatures higher than 250 °C. In as deposited 20‐ to 60‐nm‐thick Y thin films on silicon samples, crystalline Y5Si3, Si, and YSi and a 2.5‐nm‐thick amorphous layer were found to be present simultaneously. Good correlations were found among difference in atomic size between metal and Si atoms, the calculated free energy of mixing as well as the critical and maximum amorphous interlayer thickness for the Y/Si and a number of refractory metal/Si systems. The Y/Si system is the only system found up to date among all metal/Si systems that theainterlayer can be grown to a thickness exceeding 10 nm during deposition at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.353444

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An elastic continuum model is used to investigate distributions of misfit dislocations in a capped layer structure. Effects of the free surface at the top of the cap and of interactions between dislocations have been rigorously incorporated, making the study applicable to structures with caps of arbitrary thickness and to the process of strain relaxation in layers already containing misfit dislocations. Two dislocation types are considered in detail: single dislocations (singles) residing at the lower interface, between the strained layer and the substrate, and dislocation dipoles, i.e., pairs of parallel dislocations with opposite Burgers vectors, one at the lower interface and the other at the upper interface, between the strained layer and the cap. Although singles cause unwanted long‐range distortion in the cap, which is not caused by dipoles, dipoles give rise to increased localised distortion, due to the presence of the additional dislocation, at the upper interface. Hence singles and dipoles compete as misfit dislocation types in capped layers, with the dominant type being determined by the parameters of the layer structure. It is demonstrated that interactions between dislocations are crucial, and that experimental observations cannot be explained by consideration of an isolated single or dipole. Interactions between singles in an array at the lower interface result in a buildup of strain energy in the cap. The rapidity of this buildup with dislocation density demands a transition from relaxation by singles to relaxation by arrays of dipoles; such a transition would not be predicted by a consideration of isolated singles or dipoles. Energy evaluations are performed to incorporate such interactions between dislocations while providing a sequential view of strain relaxation, with singles and dipoles entering the structure one at a time. It is thus demonstrated that a mixture of singles and dipoles is expected in many capped layers of practical interest. An example calculation predicts a mixture that is consistent with experimental observation.

ISSN:0021-8979    

DOI:10.1063/1.353445

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nucleation and growth of isolated nickel disilicide precipitates in Ni‐implanted amorphous Si thin films and the subsequent low‐temperature silicide‐mediated crystallization of Si was studied usinginsitutransmission electron microscopy. Analysis of the spatial distribution of the NiSi2precipitates strongly suggested the occurrence of site saturation during nucleation. NiSi2precipitates were observedinsituto migrate through the amorphous Si thin films leaving a trail of crystalline Si at temperatures as low as ∼484 °C. Initially, a thin region of epitaxial Si formed on {111} faces of the octahedral NiSi2precipitates with a coherent interface which was shown by high‐resolution electron microscopy to be Type A. Migration of the NiSi2precipitates led to the growth of needles of Si which were parallel to ⟨111⟩ directions. The growth rate of the crystalline Si was limited by diffusion through the NiSi2precipitates, and an effective diffusivity was determined at 507 and 660 °C. A mechanism for the enhanced growth rate of crystalline Si is proposed.

ISSN:0021-8979    

DOI:10.1063/1.353446

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The laser ablation and deposition of FeSiGaRu is studied. The deposited thin films are analyzed with Auger electron spectroscopy and Rutherford backscattering spectrometry. It is found that the gallium and ruthenium content of the thin films is strongly dependent on the laser fluence. At high laser fluences (6 J/cm2) the thin films are depleted of gallium due to preferential sputtering of the gallium atoms from the thin film. Near the threshold fluence (1.9 J/cm2) the films contain an excess of gallium due to preferential evaporation of gallium from the target. The latter conclusions are based on time‐of‐flight studies of ablated atoms and ions and on measurements of the atoms that are sputtered from the substrate by the incoming flux.

ISSN:0021-8979    

DOI:10.1063/1.353447

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two aspects of the energetics of dislocation array stability in lattice‐mismatched strained layers are addressed. The first concerns criteria for determining equilibrium dislocation distributions in strained layers; the second concerns the difference between the energies of arrays of dislocations in which the Burgers vectors of all dislocations are identical, and those in which the screw components of the Burgers vectors alternate. The conclusions reached are at variance with those of recent work by Feng and Hirth on periodic arrays of dipoles in an infinite body [X. Feng and J. P. Hirth, J. Appl. Phys.72, 1386 (1992); J. P. Hirth and X. Feng, J. Appl. Phys.67, 3343 (1990)]. In particular, it is emphasized that if layers remain in equilibrium then there is always a residual mean strain; in other words, the mismatch strain is never completely relaxed. Also it is shown, via a direct calculation, that although alternating the screw components of the Burgers vectors of dislocations within asinglearray is energetically favorable, it is preferable to have all screw components of the same sign within an array iftwoorthogonalarrays are considered. Although for comparison with the work of Feng and Hirth arrays of dipoles in an infinite body are considered in more detail, the stated conclusions are also shown to hold for arrays of unpaired dislocations near a free surface.

ISSN:0021-8979    

DOI:10.1063/1.354087

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The composition of InxGa1−xAs and InyAl1−yAs epitaxial layers on InP substrates can be measured by high‐resolution x‐ray diffraction (HRXRD) in many cases. If layers are too thick, however, substantial lattice relaxation will occur, requiring multiple asymmetric scans to determine composition. If layers are too thin, they will not produce a distinct Bragg peak. Based upon measurements of both coherent and relaxed layers as well as simulations, we have determined the range of epilayer thickness over which a single HRXRD scan yields the composition of InxGa1−xAs and InyAl1−yAs layers to within 1%. Calibration layers grown within this range allow fast and accurate characterization.

ISSN:0021-8979    

DOI:10.1063/1.353448

出版商:AIP    

年代:1993

数据来源: AIP