The deposition of InAs on GaAs proceeds first by two-dimensional (2D) growth and above a 1.75-monolayer coverage by the formation of single-crystal dots on a residual 2D wetting layer. By atomic force microscopy measurements, we show that the first dots formed are in the quantum size range (height 30 Å, half-base 120 Å), that the dispersion on their sizes is remarkably low (±10%), and that they are located fairly regularly (interdot distance 600 Å). Upon further growth, density and shapes do not change but sizes increase up to double values before coalescence occurs. Self-organized growth in strained structures is then shown to be a simple and efficient way of building regular quantum dots.

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We have investigated light propagation in optical devices by near-field scanning optical microscopy (NSOM) at the telecommunication wavelength of 1.55 μm. NSOM images obtained on the top of channel waveguides measure the mode profile perpendicular to the propagation direction and show a modulation of intensity along this direction. This modulation demonstrates the periodic variation of the mode size predicted for the propagation in small guides and marks the direction of propagation. We show that NSOM analysis can completely assess complex optical devices with subwavelength resolution: determination of the optical path, variation of the light intensity along this path, and measurement of local radiative losses.