Location of the H1⁄2þ= level: Experimental limits for muonium

The defect energy levels for muonium, a light pseudo-isotope of hydrogen, are investigated to define the equivalent of the H1⁄2þ= level which is predicted to be fixed at a universal energy. Existing results for Mu at donor and acceptor sites in silicon tentatively place Mu1⁄2þ= approximately 0.5 eV above the predicted hydrogen level. Measured donor ionization energies in other materials in which two neutral Mu centers are observed define a range for the Mu acceptor energies. We discuss possible reinterpretation of known energies and the current state of investigations to obtain these muonium acceptor levels in order to further refine a determination of the Mu1⁄2þ= energy. r 2006 Elsevier B.V. All rights reserved. PACS: 71.55. i; 76.75.+i