Adatom aggregation, reaction, and chemical trapping at the Sm/GaAs(110) interface

Synchrotron radiation photoemission has been used to study the room-temperature formation of the Sm/GaAs(110) interface. Valence-band, 4f emission, and high-resolution core-level results show the existence of distinct stages corresponding to chemisorption and agglomeration of Sm atoms (coverage CTHETA≲1 Å), reactive interdiffusion (1≲CTHETA≤6–8 Å), and growth of metallic Sm. The final value of the Schottky barrier (0.63 eV) is also attained by CTHETA=1 Å even though Sm is present only in the divalent or unreacted atomic configuration. Heterogeneous intermixing and reaction occur above CTHETA∼1 Å and the trivalent configuration of Sm dominates. Large chemical shifts of the As 3d (1.02±0.05 eV) and Sm 4f (1.55±0.10 eV) cores demonstrate the formation of Sm–As bonds with substantial charge transfer in the intermediate-coverage range. This is confirmed by the appearance of a prominent As p–derived valence-band peak at -2.4 eV and the low emission at the Fermi level. Above CTHETA=6–8 Å, the increasing emission near $E_F$ and the decrease of the trivalent to divalent 4f intensity ratio shows the growth of a Sm-rich layer. Convergence to bulk Sm occurs above CTHETA=20 Å. The extremely rapid attenuation of both As and Ga core-line intensities indicates exceptionally strong anion and cation trapping in the thin reacted layer.