Vertical composition fluctuations in (Ga,In)(N,As) quantum wells grown on vicinal (1Â 1Â 1)B GaAs

In this work, we present a detailed transmission electron microscopy analysis of the interfacial structure and composition uniformity of (Ga,In)(N,As) quantum wells grown by molecular beam epitaxy on vicinal GaAs(1 1 1)B substrates. Vertical composition fluctuations inside the (Ga,In)(N,As) quantum well are detected depending on the growth conditions, in particular the V/III flux ratio and the growth rate. This vertical composition fluctuation due to the phase separation tendency is in contrast to the (0 0 1) case, where the fluctuations proceed in the lateral direction. The specific character of the phase instabilities is discussed with respect to the spinodal decomposition of the (Ga,In)(N,As) alloy grown by step-flow on the misoriented (1 1 1)B substrates. The vertical composition fluctuations are explained by the formation of step bunches of alternating composition as a consequence of the different propagation velocity of steps with different atom terminations.