Atomic structure of the "non-polar" (110) surface of some III-V compound semiconductors. (a) The ideal, bulk-like, unrelaxed surface of GaAs(110). (b) The actual structure involves a relaxation which results in almost planar arangement of the first three atomic planes. The gallium atoms have sp2 bonding configuration while the arsenic atoms have filled dangling bond states. This configuration leaves no surface states in the middle of the band gap.