THEORIGIN OF THE LOW RESISTIVITY IN Ge-ION IMPLANTED ZnO BULK SINGLE CRYSTALS

The origins of low resistivity in Ge ion-implanted ZnO bulk single crystals are studied by Van der Pauw methods, photoluminescence (PL), Rutherford backscattering spectroscopy (RBS) and Nuclear reaction analysis (NRA). The resistivity decreases from ~103 Ωcm for un-implanted samples to 1.45 × 10-2 Ωcm for as-implanted, and 6.26 × 10-1 Ωcm for 1000 ºC annealed samples. In RBS and NRA measurements, the Zn interstitial acts as shallow donor and the O interstitial acts as acceptor are observed. A new PL emission appears at around 372 nm (3.33 eV) after annealing at 1000 ºC, suggesting Ge donors with an activation energy of 100 meV. This value corresponds to the activation energy (102 meV) of Ge donors estimated from the temperature dependence of carrier concentration. The origin of the low resistivity in as-implanted samples is attributed to the Zni (~30 meV). In contrast, the origins of the low resistivity in 1000 ºC annealed samples are assigned to both the Zni related defects and the electrically activated Ge donor