An atomistic study of the GaAs-Pd interface

The interface of GaAs-Pd was investigated on an atomic scale by a time-of-flight (TOF) atom-probe field ion microscope (FIM). It was found that Pd reacts strongly with Ga even at room temperature to form a stable PdGa compound. Depending upon heat treatment conditions, several types of Pd-(Ga, As) ternary compounds were also formed. A thin layer (less than a few monolayers) of As was quite often detected at the outermost surface layer when the interface was heated up to 400°C. Above 400°C only the most stable PdGa phase was observed at the interface. At a temperature range between 200 and 400°C, the segregated Ga phase was also found beneath the As layer. The interfacial reactions can be understood by the following two processes: (1) Pd atoms diffuse into the GaAs substrate to form a stable Pd-Ga bond and (2) As, whose bonding with Ga is broken, becomes loose and migrates to the surface and desorbs.