Sparse-carrier devices and method of fabrication

A sparse-carrier device comprising:

• a crystal structure formed of a first material and having a crystallographic facet with a width and a length, the crystallographic facet having contact structures at opposite ends of the length;
• quantum dots formed of a second material and positioned in a plurality of rows on the crystallographic facet, each row extending along the length of the crystallographic facet and being approximately one quantum dot wide and a plurality of quantum dots long, the crystallographic facet being defined with a width to restrict formation of the second material thereon to the plurality of quantum dot wide rows of quantum dots, the quantum dots in a first row of the plurality of rows being separated from adjacent quantum dots in the first row by a first distance smaller than a second distance between the quantum dots in the first row and adjacent quantum dots in an adjacent row, and the quantum dots in the adjacent row being separated from adjacent quantum dots in the adjacent row by the first distance smaller than the second distance between the quantum dots in the adjacent row and adjacent quantum dots in the first row, the first distance being small enough to allow carrier tunneling between adjacent quantum dots and the second distance being large enough to substantially prevent tunneling between adjacent quantum dots and small enough to allow Coulombic interaction between adjacent quantum dots;
• and
• electrical contacts positioned on the contact structures at opposite ends of the length, the electrical contacts being spaced from the quantum dots in the plurality of rows a distance to allow tunneling of carriers into and out of quantum dots in the plurality of rows, wherein a first row of the plurality of rows of quantum dots is connected to receive input signals and a second parallel spaced apart row of the plurality of rows of quantum dots is connected to provide an output signal. and wherein quantum dots in the second row are charged oppositely to quantum dots in the first row by Coulombic interaction between adjacent quantum dots so that output signals from the second row are inverted from input signals supplied to the first row.