Techniques for realizing linearly graded composition or doping profiles in MBE materials.

Linear grading of alloy composition in MBE materials is more complex than it first appears because of the effect of changing beam flux on the growth rate and the nonlinear dependence of beam flux on the effusion-cell temperature. In this paper, mathematical relations between the effusion-cell temperature and time that must be followed during MBE growth to produce a linearly graded depth profile of alloy composition or doping concentration are derived. Implementation of this relation in a programmable controller using a novel dual timer technique for effusion-cell temperature control is also described. The validity of this technique is demonstrated experimentally for compositional grading as well as doping concentration grading.