Etching of the InP(001) Surface by Halogens:  Reaction Mechanisms Obtained by Density-Functional Calculations

Reaction energies and related barrier heights of halogenated InP(001) surface structures are calculated using the density functional theory and molecular models for typical local surface structures. The obtained data show how the elementary mechanisms of the chemical etching depend on the applied halogen (X = F, Cl, Br, I). Two reaction regimes are determined, which are consistent with the α and β state discussed for the Cl2+InP(001) system: Under low halogenation (β-state) the In atoms leave the surface as InX (19−35 kcal/mol). The P atoms are removed as P2 (32−37 kcal/mol) or after combination as P4 independently of the used halogen. Formed PF, PCl, PBr, and InX2 surface groups require a higher energy expense (> 50 kcal/mol) or a higher halogenation for the desorption. A smaller energy is necessary for the PI removal (37 kcal/mol). Under high halogenation (α-state), In atoms could leave the surface as InX3 (F: 21 kcal/mol; Cl, Br, I: 7−10 kcal/mol). However, a relatively stable corrosion phase composed of bound InX3 molecules is formed on the surface. P atoms can be removed as PX3 (20−24 kcal/mol) or PX2 (26−31 kcal/mol). The rate-limiting steps are the P2 and the PX3 (InF3) desorption for low and high halogenation, respectively. Practically, a higher temperature has to be used for obtaining a high etch rate by reason of the transport of the etch gas to and the products from the surface.