Percolation of quantum Hall droplets in intentionally disordered GaAs/GaAlAs heterojunctions

The transition of two-dimensional electron systems (2DES) with intentional disorder in form of a δ-layer doped with beryllium into quantum Hall insulators composed of separate electron droplets is examined by magnetotransport and far-infrared spectroscopy. We observe the percolation threshold at filling factors clearly below View the MathML source that is expected for statistical disorder. The far-infrared excitations bear strong resemblance to magnetoplasmons of density-modulated 2DES and antidot systems in regular arrays. Thus, a perceptible degree of short-range order between the sites of the beryllium acceptors is uncovered.