Excitonic positronium emission fromn-Si(111)

Recently it was found that energetic positronium (Ps) emission from both n- and p-type Si(100) occurs primarily via an exciton-like surface state PsX. The underlying Ps production mechanism was deduced from the observed Ps emission yield and kinetic energy, using laser and thermally generated electrons to populate the PsX state, but not all of the observed effects have been explained. In this brief report we show that excitonic Ps emission also occurs from n-Si(111), but with characteristics that more closely resemble p-Si(100) than n-Si(100). Considering both (100) and (111) crystal orientations may help in the formulation of a more complete theoretical description of the excitonic Ps production mechanism. © 2012 American Physical Society.