Transmission electron microscopy of Ga(Sb, Bi)/GaSb quantum wells with varying Bi content and quantum well thickness

We analyze the microstructure of a series of Ga(Sb, Bi)/GaSb quantum wells (QW) with varying Bi content and QW thicknesses using transmission electron microscopy. The structures are grown on GaSb(001) substrates by low-temperature molecular beam epitaxy. Although Ga(Sb, Bi) is regarded as a highly-mismatched alloy, the material is of remarkable quality and no extended defects or nanoclusters are detected in the pseudomorphic layers. Regardless their different Bi content (ranging from 4% to 11%) all QW samples seem to be homogeneous in composition and no composition fluctuations are detected. The QW/barriers are nevertheless affected by thickness fluctuations, where the thickness slightly varies from QW to QW but also laterally. Despite the samples exhibit well-defined QW/barrier interfaces, we note that the Ga(Sb, Bi)-on-GaSb interface is rougher than the GaSb-on-Ga(Sb, Bi) one. The morphological smoothing effect at the GaSb-on-Ga(Sb, Bi) interface is attributed to the well-known surfactant behavior of Bi in connection with Bi surface segregation, as evidenced from experimental Bi distribution profiles. (paper)