Successful growth of ErSb(001) single crystal layers on GaSb(001) substrates has been demonstrated. The reflection high-energy electron diffraction patterns show a (4×4) surface reconstruction. Reflection high-energy electron diffraction oscillations, x-ray diffraction, and Rutherford backscattering with channeling indicate single crystal monolayer-by-monolayer growth and continuity of the Sb sublattice at the ErSb/GaSb interface. The ErSb has a low room temperature resistivity equal to 30 μΩ cm but may be used as a metallic reflector only for wavelengths greater than 2.4 μm. The overgrowth of GaSb on ErSb leads to mirrorlike surfaces but the overlayers contain symmetry-related defects. On the contrary, nearly perfect GaSb overlayers were grown on [ErSb,GaSb] superlattices which exhibit metallic behavior.