Nucleation mechanisms and the elimination of misfit dislocations at mismatched interfaces by reduction in growth area

Abstract

To investigate the effect of growth area on interface dislocation density in strained-layer epitaxy, we have fabricated 2-.um-high mesas of varying lateral dimensions and geometry in (001) GaAs substrates with dislocation densities of 1.5 X 10\ 10 4 , and 10 2 cm--2 • 3500-, 7000-, and 8250-A-thick In o (J5 Gao 95 As layers, corresponding to 5, to, and 11 times the experimental critical layer thickness as measured for large-area samples, were then deposited by molecularbeam epitaxy. For the 3500-A layers, the linear interface dislocation density, defined as the inverse of the average dislocation spacing, was reduced from greater than 5000 to less than 800 em -I for mesas as large as 100 pm. A pronounced difference in the linear interface dislocation densities along the two interface (110) directions indicates that a dislocations nucleate about twice as much as /3 dislocations. For samples grown on the highest dislocation density substrates, the linear interface-dislocation density was found to vary linearly with mesa width and to extrapolate to a zero linear interface-dislocation density for a mesa width of zero. This behavior excludes dislocation multiplication or the nucleation of surface half"loops as operative nucleation sources for misfit dislocations in these layers. Only nucleation sources that scale with area (termed fixed sources) are active. In specimens with lower substrate dislocation densities, the density of interface dislocations still varies linearly with mesa size, but the slope becomes independent of substrate dislocation density, indicating that surface inhomogeneities now act as the dominant source for misfit dislocations. Thus, in 3500-A-thick overlayers, substrate dislocations and substrate inhomogeneities are the active fixed nucleation sources. Since only fixed nucleation sources are active, a single strained layer wiH dramatically reduce the threading dislocation density in the epilayer. For the 7ooo-A layers, we observe a superlinear increase in linear interface-dislocation density with mesa size for mesas greater than 200,um, indicating that dislocation mUltiplication occurs in large mesas. For mesas less than 200 pm in width, linear interface-dislocation density decreases linearly with mesa size, but extrapolates to a nonzero linear interface-dislocation density for a mesa size of zero. This nonzero extrapolation suggests an additional active source which generates a dislocation density that cannot be decreased to zero by decreasing the mesa size. Cathodoluminescence eeL) images using radiative recombination indicate that the additional source is nucleation from the mesa edges. Despite a doubling in epilayer thickness from 3500 to 7000 A, the linear interface-dislocation density for mesas 100 [tm in width is stm very low, approximately 1500 cm --l. The 8250"A layers possess interface-dislocation densities too high to be accurately determined with CL. However, increases in CL intensity as mesa width is reduced indicate that the interface-dislocation density is decreasing and that growth...

Misfit Dislocations in Epitaxial Heterostructures: Mechanisms of Generation and Multiplication

“…A part of these mechanisms is concerned with heterogeneous dislocation nucleation at some particles (b-SiC precipitates [14] or oxide particles [15]) remaining at the substrate surface or so-called diamond defects [19]. We will not consider these mechanisms in detail.…”

“…1 for heterostructures with an alloy composition of 4 at% Ge. At the initial stage of misfit strain relaxation, MDs generate from sources of primary generation (dislocations propagating from the substrate into the layer [13], precipitates [14] or oxide particles [15] remaining at the substrate surface etc.) and a regular MD network forms (Fig.…”

Incorporation of Sb and As in MBE grown GaAsxSb1−x layers

“…At higher T g the reaction happens more frequently since the energy barrier for this reaction is more easily overcome. Since the imperfections such as particulates and impurities strongly influence the relaxation of strain in epitaxial layers, 22,23 the early relaxation of GaAs x Sb 1x layers grown at low growth rates can be linked to the presence of AsSb clusters originating from the As-for-Sb exchange reaction. Of the three mechanisms proposed in the literature to describe the incorporation of Sb into GaAs x Sb 1x layers, the As-for-Sb exchange reaction is the only one which can describe all aspects found in the experiments.…”

Threading dislocation removal from the near-surface region of epitaxial cadmium telluride on silicon by lithographic patterning of the substrate

“…Trenches in the material can be used as sinks for dislocations. This approach has been applied successfully to other materials systems, including GaAs on Si, 5 In x Ga 1-x As on GaAs, 6,7 10 To test this approach for CdTe on Si, we have patterned Si wafers into an array of mesas surrounded by trenches and then deposited CdTe on them. We anneal the epilayers during growth to set the dislocations in motion.…”