6.5 INVERTED-PYRAMID QUANTUM DOTS

In the previous sections, it was shown that the self-limiting growth by OMCVD on V-grooved (100) GaAs substrates is useful for the preparation of high quality QWRs. In this section, an extension of this technique for the fabrication of QDs with comparable interface quality and structural control will be described.

Similar to the V-groove QWR case, the realization of such self-ordered QDs requires the identification of a suitable set of crystalline facets that exhibit the characteristic self-limiting growth. In addition, control of the self-limiting profile via the adjustment of the surface diffusion length is necessary in order to control the size and shape of the resulting 0D structure. However, different from the QWR case, where a self-limiting wedge between two (nearly) identical {111} A facets defines a 2D growth template, the formation of the QDs requires 3D self-limiting surface patterns. The simplest crystallographic configuration, which resembles most closely the V-groove QWR case, is the corner formed by three {111}A planes. Such a corner can be realized using a pyramidal recess etched into a GaAs (111)B-oriented wafer [72, 73]. Other 3D geometries utilized for the formation of nonplanar QD heterostructures are tetrahedral mesas grown on GaAs (111)B substrates [201], and square-based inverted pyramids grown on GaAs (100) wafers [202] using selective OMCVD growth on masked surfaces.

In the following, the approach using pyramidal recesses etched into GaAs (111)B substrates will be discussed in some detail. An array of such inverted pyramids, which is produced by optical lithography,...