Large energy shifts in the luminescence emission from strained InGaAs quantum dots are observed as a result of postgrowth annealing and also when raising the upper cladding layer growth temperatures. These blueshifts occur concurrently with narrowing (from 61 to 24 meV) of the full width at half-maxima for the emission from the quantum dot ensemble. These energy shifts can be explained by interdiffusion or intermixing of the interfaces rather than strain effects due to variations in capping layer thickness. Temperature behavior of the luminescence in annealed and nonannealed samples indicates a change in the shape and depth of the quantum dot confining potential. Quenching of the wetting layer luminescence after interdiffusion is also observed.

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We report significant differences in the temperature-dependent and time-resolved photoluminescence ͑PL͒ from low and high surface density In x Ga 1Ϫx As/GaAs quantum dots ͑QD's͒. QD's in high densities are found to exhibit an Arrhenius dependence of the PL intensity, while low-density ͑isolated͒ QD's display more complex temperature-dependent behavior. The PL temperature dependence of high density QD samples is attributed to carrier thermal emission and recapture into neighboring QD's. Conversely, in low density QD samples, thermal transfer of carriers between neighboring QD's plays no significant role in the PL temperature dependence. The efficiency of carrier transfer into isolated dots is found to be limited by the rate of carrier transport in the In x Ga 1Ϫx As wetting layer. These interpretations are consistent with time-resolved PL measurements of carrier transfer times in low and high density QD's. ͓S0163-1829͑99͒04748-7͔

Many of the structural elements of importance in materials applications (e.g., thin films, barrier layers, intergranular films in ceramics) are small in volume and amorphous. Although the characterization of the structure of amorphous materials by X-ray and neutron diffraction methods is well established, these techniques are not suitable for studies of nanovolumes of materials because of the relatively small scattering cross sections. This chapter reviews recent developments in electron techniques, and particularly electron diffraction, for overcoming this problem.