Using atomic force microscopy (AFM) imaging, transmission electron microscopy (TEM) and photoluminescence (PL), we have studied InAs stacked islands on InP(001) versus the InAlAs spacer layer thickness (SLT). We have found that first wire-libe island shape is strongly favored by such a stacking process and second in the 10-25 nm SLT range, the wire size and height are dependent on the SLT. TEM images show off a new surprising staggered vertical island organization that can be explained by the phase separation appearing in the InAlAs spacer layers.