We demonstrate the growth by molecular beam epitaxy of a metal/semiconductor composite consisting of epitaxial semimetallic ErSb particles in a GaSb matrix. The ErSb nucleates in an island growth mode leading to the spontaneous formation of nanometer-sized particles. These particles are found to preferentially grow along a  direction on a (100) GaSb surface. The particles can be overgrown with GaSb to form an epitaxial superlattice consisting of ErSb particles between GaSb spacer layers. The size of the ErSb particles increases monotonically with the deposition. The carrier concentrations in the superlattices are found to be dependent on both the size and density of the ErSb particles. Smaller particles and closer layer spacings reduce the hole concentration in the film. (C) 2004 American Institute of Physics.