Electronic coupling and structural ordering of quantum dots using InAs quantum dot columns

In this article, recent investigations of vertically aligned quantum dot columns conducted at Stanford University are reviewed. The quantum dots are InAs in a matrix of GaAs. Both the quantum dots and quantum dot columns are formed through strain-induced islanding, without lithography. Two aspects of these columns are discussed. First, the electronic coupling of quantum dots within columns of up to ten quantum dots is demonstrated. The coupling is adjusted and improvements to a simple light-emitting diode are shown. Second, increased uniformity of a surface quantum dot layer is shown when a subsurface layer of these columns are used. The most impressive results occur when the columns contain a large number of islands. Reduced variations in average ensemble height and diameter, called size uniformity, and average nearest neighbor distances, called structural uniformity, are shown. A surface unit cell of islands is demonstrated and the lack of a surface lattice is discussed.