Heavy carbon doping of AlAs by elemental-source molecular beam epitaxy

Heavily carbon-doped AlAs films with free-hole concentrations in excess of 10¹⁹ cm^–3 have been grown by conventional molecular beam epitaxy using elemental sources. The hole concentration in AlAs:C saturates at 6×10¹⁹ cm^–3 without any detectable deterioration of the smooth surface morphology and of the structural properties. At very high carbon concentrations the lattice contraction due to the smaller covalent radius of carbon leads to an in-plane lattice constant of the AlAs:C films which is even smaller than that of the GaAs substrate. The high freehole concentration and the tunability of the lattice constant are important for application in p-type GaAs/AlAs Bragg reflectors in surface emitting lasers having a low series resistance and a significantly reduced lattice mismatch.