Growth of a three-dimensional anisotropic lattice of Ge quantum dots in an amorphous alumina matrix

Simple processes for the preparation of semiconductor quantum dot lattices embedded in dielectric amorphous matrices play an important role in various nanotechnology applications. Of particular interest are quantum dot lattices with properties that differ significantly in different directions parallel to the material surface. Here, a simple method is demonstrated for the fabrication of an anisotropic lattice of Ge quantum dots in an amorphous Al₂O₃ matrix by a self-assembly process. A specific deposition geometry with an oblique incidence of the Ge and Al₂O₃ adparticles was used during magnetron sputtering deposition to achieve the desired anisotropy. The observed Ge quantum dot ordering is explained by a combination of directional diffusion of adparticles from the Ge and Al₂O₃ targets and a shadowing process which occurs during deposition as a result of the specific surface morphology. The prepared material shows a strong anisotropy of the electrical conductivity in different directions parallel to the sample surface.