Semi-insulating properties of GaAs with artificially buried W discs

In this paper we review our experiments in which a controlled formation of semi-insulating GaAs by introduction of buried metal discs is demonstrated. A tungsten disc matrix is embedded in an epitaxial layer by epitaxial overgrowth and the current transport perpendicular to the lattice is studied. The discs form Schottky barriers to the surrounding GaAs, which is depleted from free carriers. The conductance is demonstrated to vary by 7 orders of magnitude in structures as a function of varying disc separation. Using such a semi-insulating structure with a high disc density, the buried contacts have been characterised by photo-conductivity measurements and space-charge spectroscopy. The experimental results are in excellent agreement with an analytical model for depletion and charging of nano-scale Schottky barriers.