The electronic structure and the location of muonium centers in single-crystalline ZnO were determined for the first time. Two species of Mu centers with extremely small hyperfine parameters were observed below 40K. Both Mu centers had an axial-symmetric hyperfine structure along with a <00•1> axis, indicating that they were located at the antibonding (ABO,||) and bond-center (BC||) sites. It was inferred from their small ionization energy (about 0.006 and 0.050eV) and hyperfine parameters (some 10–4 times the vacuum value) that these centers behaved as shallow donors, strongly suggesting that H was one of the primary origins of n type conductivity in as-grown ZnO.

Electronic Structure of the Muonium Center as a Shallow Donor in ZnO. K.Shimomura, K.Nishiyama, R.Kadono: Physical Review Letters, 2002, 89[25], 255505 (4pp)