Recent molecular dynamics simulations of the growth of $[{\mathrm{Ni}}_{0.8}{\mathrm{Fe}}_{0.2}/\mathrm{Au}]$ multilayers have revealed the formation of misfit-strain-reducing dislocation structures very similar to those observed experimentally. Here we report similar simulations showing the formation of edge dislocations near the interfaces of vapor-deposited (111) [NiFe/CoFe/Cu] multilayers. Unlike misfit dislocations that accommodate lattice mismatch, the dislocation structures observed here increase the mismatch strain energy. Stop-action observations of the dynamically evolving atomic structures indicate that during deposition on the (111) surface of a fcc lattice, adatoms may occupy either fcc sites or hcp sites. This results in the random formation of fcc and hcp domains, with dislocations at the domain boundaries. These dislocations enable atoms to undergo a shift from fcc to hcp sites, or vice versa. These shifts lead to missing atoms, and therefore a later deposited layer can have missing planes compared to a previously deposited layer. This dislocation formation mechanism can create tensile stress in fcc films. The probability that such dislocations are formed was found to quickly diminish under energetic deposition conditions.

Misfit-energy-increasing dislocations in vapor-deposited CoFe/NiFe multilayers

Semiconductor structures and devices including strained material layers having impurity-free zones, and methods for fabricating same. Certain regions of the strained material layers are kept free of impurities that can interdiffuse from adjacent portions of the semiconductor. When impurities are present in certain regions of the strained material layers, there is degradation in device performance. By employing semiconductor structures and devices (e.g., field effect transistors or “FETs”) that have the features described, or are fabricated in accordance with the steps described, device operation is enhanced.

Semiconductor structures employing strained material layers with defined impurity gradients and methods for fabricating same

Instabilities in crystal growth by atomic or molecular beams

Heterostructures in the form of thin layers of one material grown on a substrate have been the subject of intense study for several years. In the case of semiconductor systems the aim is to grow epitaxial layers of, for example, Si1-xGex on Si, and devices based on such structures are already in use. Much is known, as is summarized in this review, about the stability of such systems against the insertion of dislocations, and about the critical thicknesses up to which strained layer structures are stable. The effects of dislocation nucleation and the dynamics of dislocation motion which lead to strain relaxation in metastable systems are also reviewed. The present state of theoretical understanding is compared with what is known experimentally. For metallic systems, which often exhibit magnetic properties, the underlying problems of lattice mismatch and strain relief are similar, but much of the interest has been concentrated on the commensurate-incommensurate transition in both structurally and m...

Misfit strain and misfit dislocations in lattice mismatched epitaxial layers and other systems

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

An exact closed-form formula is given for the energy of an array of dislocations, arranged periodically on the interface between an epitaxial layer and its substrate, when these are modelled as elastically isotropic with the same elastic constants. In the course of the formulation, the exact equivalence of equilibrium theories originating in the work of Frank and van der Merwe and of Matthews and Blakeslee is established. The new formula allows the exact assessment of arrays of dislocations in equilibrium, for layers thicker than critical. This demonstrates that previous approximations may be seriously in error.

The energy of an array of dislocations: Implications for strain relaxation in semiconductor heterostructures

(1990). A review of theoretical and experimental work on the structure of Ge x Si1-x strained layers and superlattices, with extensive bibliography. Advances in Physics: Vol. 39, No. 2, pp. 127-190.

A review of theoretical and experimental work on the structure of GexSi1-x strained layers and superlattices, with extensive bibliography

The predicted energy of an array of dislocations in semiconductor epilayers is considerably reduced due to interactions between the dislocations. It is found that when the effects of interactions are taken into account, the existing expression for critical layer thickness hc becomes invalid. A method to calculate the correct critical layer thickness hci' taking into account the interactions, is given. Values of hci are always smaller than hc but the difference hc—hci is small. The concentration of dislocations present in thick epilayers (i.e. with hhci) in stable equilibrium increases considerably due to interactions. The rates of plastic flow and strain relaxation on annealing the metastable epilayers also increase. The values of phenomenological constants present in the plastic flow theories which are used to interpret experiments are much reduced when interactions are properly taken into account.

A new study of critical layer thickness, stability and strain relaxation in pseudomorphic gexsi1-x strained epilayers

Two guiding principles for the determination of stable configurations in strained epitaxial layers (epilayers) are considered. One states that dislocations will be introduced so that the epilayer attains the lowest-energy configuration. The other considers the force acting on a threading dislocation, tending to drive it across the epilayer, depositing a misfit dislocation as it moves: the Matthews-Blakeslee force balance model states that strain relaxation will occur via threading motion until the force due to the relaxed strain is insufficient to drive a dislocation across the epilayer. It is demonstrated in this work that previously neither of these principles has been correctly applied. An exact solution for the energy of a period array of misfit dislocations has recently become available, which makes a precise analysis possible. The correct application of the energy minimization and force balance principles is discussed and the relationship between the two approaches is clarified. An exact ex...

Stable configurations in strained epitaxial layers

An analysis is presented of the energy of a periodic array of pairs of dislocations in an infinite body It is then applied to the assessment of the energy changes induced by the introduction of a dipole-like array, on the upper and lower surfaces of a capped epitaxial layer The analysis is sufficiently simple that ‘compound arrays’ can also be assessed General formulae are presented and it is shown, in a particular case, that arrays generated by symmetrical slip from nuclei on one interface relax the mismatch with a smaller energy penalty than a simple array Other compound arrays will exist which display the same property It is concluded that mechanisms other than the introduction of threading dislocations are likely to be of relevance to the degradation of some semiconductor heterostructures

R. Bullough

Papers

The energy of an array of dislocations: Implications for strain relaxation in semiconductor heterostructures

A review of theoretical and experimental work on the structure of GexSi1-x strained layers and superlattices, with extensive bibliography

A new study of critical layer thickness, stability and strain relaxation in pseudomorphic gexsi1-x strained epilayers

Stable configurations in strained epitaxial layers

The energy of an array of dislocations. II, Consideration of a capped epitaxial layer