BOND-LENGTH ANOMALY IN INP1-XASX MONOLAYERS ON INP(001) STUDIED BY EXTENDED X-RAY ABSORPTION FINE STRUCTURE

The bond-length relaxation in InP1−xAsx monolayers epitaxially grown by metalorganic vapor-phase epitaxy on an InP(001) substrate has been investigated using the extended x-ray absorption fine structures on the As K edge. The In–As bond lengths in InP1−xAsx monolayers were determined over a wide range of As composition x (0.08bond length RIn–As in InP1−xAsx monolayer shows an anomaly at x∼0.5; RIn–As is compressed at x∼0.5, deviating from the linear interpolation between the values in a dilute limit (x<<1, As:InP) and the strained InAs monolayer (x=1). The As composition dependence of RIn–As coincides with that observed for As atoms incorporated by a surface As–P exchange reaction. The mechanism of anomalous bond-length variation, associated with the change of local structure from the dilute limit to the strained monolayer, is discussed in terms of the elastic energy confined in a strained heterointerface.