Effective constant doping in a graded compositional alloy

Abstract

Epitaxial growth of a chirped superlattice with constant dopings is achieved with minimal growth interruption time. This is done by doping only one of the two compositions during growth of its layer. For example, in the growth of a plurality of alternating layers of InP and GaInAs to form the superlattice, either the InP layers are doped with an n-type dopant, such as silicon, or the GaInAs layers are doped with a p-type dopant, such as beryllium. Alternatively, InP can equally be doped p-type (with beryllium) and GaInAs can be doped n-type (with silicon). In either case, the doping scheme described herein is easily done during molecular beam epitaxial growth by opening and closing the shutter of the dopant (silicon or beryllium) source cell at the appropriate times. To the electrical carriers, the doping superlattice scheme of the present invention presents a uniform doping without any need to change the doping cell temperature. This in turn allows improved controllability and minimal interface contamination.