Atomic force microscope (AFM) imaging and cross-sectional analysis were used to document the shape evolution of Ge/Si(100) islands, grown by molecular beam epitaxy, as a function of growth conditions. Growth temperatures of 450, 550, 600, and 650 °C with Ge coverages between 3.5 and 14.0 monolayers (ML) were investigated for a deposition rate of 1.4 ML/min. Low coverages produced small hut clusters which then evolved into dome clusters at higher coverages. These dome clusters eventually dislocated after further growth. Higher growth temperatures activated additional pathways for the Ge islands to relieve their strain such as Ge/Si intermixing and the formation of trenches around the islands. Our detailed AFM cross-sectional analysis indicated that dome clusters form several crystal facets in addition to those previously reported.

Ge͞Si͑100͒ island size distributions were monitored for coverages between 3.5 and 14.0 monolayers at growth temperatures from 450 to 600 ± C. Features in these distributions are correlated with characteristic island morphologies. The mean dome cluster size increased and the onset of island dislocation was delayed as the growth temperature increased. At 600 ± C, very large hut clusters are formed. This behavior is attributed to strain-assisted alloying of the Ge clusters. Energy dispersive x-ray analysis confirms Si diffusion into the Ge clusters at 600 ± C. An atomistic elastic model supports the interpretation that alloying is driven by strain energy enhancement near the island perimeters.

Trenches formed at Ge/Si(100) island bases become an effective strain-relief mechanism at high growth temperatures. Trenches result from diffusion of the most highly strained material to regions of lower strain. The trench depth self-limits, scaling linearly with island diameter. A simple atomistic model of island elasticity indicates that this self-limiting behavior is of kinetic rather than energetic origin.

No abstract

No abstract

No abstract

The normalized width=standard deviation of island radius/mean island radius (σr/〈r〉) of molecular beam epitaxy grown Ge on Si(100) coherent island quantum dot size distributions is analyzed for various deposition conditions. It is found that this width decreases as substrate temperature increases independent of deposition flux. This result is interpreted in the context of models which suppose that the energy barrier for edge atom detachment decreases with island size. The faster diffusion kinetics at higher growth temperatures allow these detached edge atoms to more rapidly find the smaller islands producing sharper island size distributions.

The optimized growth conditions and evidence for type-II alignment in GaAsSb/InGaAs heterostructures are reported. The asymmetric GaAsSb/InGaAs bilayer quantum well grown on GaAs shows promising results for device applications around the wavelength of 1.3 m. Uncompensated type-II GaAs/GaAsSb/GaAs quantum-well systems and strain-compensated GaAsP/GaAs/GaAsSb/GaAs/GaAsP quantum-well systems are compared for 1.3 m applications. Inhomogeneous photoluminescence-linewidth broadening due to lateral composition and thickness variation is reduced from 74 to 40 meV when GaAsP strain-compensation layers are added to GaAsSb-based trilayer quantum-well systems.