Differences between the In_yGa_1-yAs/GaAs interface and GaAs/In_yGa_1-yAs interface in superlattice over a In_xGa_1-xAs (x<y) buffer layer

The In_yGa_1-yAs/GaAs superlattice on In_xGa_1-xAs (x<y) buffer layer was grown by MOCVD. The well layer is under compressive strain and the barrier layer is under tensile strain. However, both layers do not exceed the calculated critical value based on the M&B equilibrium theory. According to the measuring results of TEM, SIMS, we found that: the GaAs/In_yGa_1-yAs interface was smoother than the In_yGa_1-yAs/GaAs interface; the Indium composition gradual region at the GaAs/In_yGa_1-yAs interface was narrower than that at the In_yGa_1-yAs/GaAs interface; in In_yGa_1-yAs alloy layer, the Indium composition near the GaAs/In_yGa_1-yAs interface was higher than that near another interface. For the first time, we explained the composition profile in this kind of superlattice based on the indium segregation theory. A new strain relaxation model, in which the 30-degree and 90-degree shockley partial dislocations were taken into account under both tensile and compressive strains, was presented to explain the difference of the smoothness between the GaAs/In_yGa_1-yAs interface and the In_yGa_1-yAs/GaAs interface.