Origins of low resistivity in Ai ion-implanted ZnO bulk single crystals

摘要

The origins of low resistivity in Al ion-implanted ZnO bulk single crystals are studied by combining Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), photoluminescence (PL), and Van der Pauw methods. The Al-ion implantation (peak concentration: 2.6 × 10~(20)cm~(-3)) into ZnO is performed using a multiple-step energy. The resistivity decreases from ～104 Q cm for un-implanted ZnO to 1.4 × 10~(-1) Ω cm for as-implanted, and reaches 6.0 × 10~(-4) Ω cm for samples annealed at 1000 ℃. RBS and NRA measurements for as-implanted ZnO suggest the existence of the lattice displacement of Zn (Zn_i) and O (O_i), respectively. After annealing at 1000 ℃, the Zn_i related defects remain and the O_i related defects disappear. The origin of the low resistivity in the as-implanted sample is attributed to the Zn_i (～30 meV [Look et al., Phys. Rev. Lett. 82, 2552 (1999)]). In contrast, the origin of the low resistivity in the sample annealed at 1000 ℃ is assigned to both of the Zn_i related defects and the electrically activated Al donor. A new PL emission appears at around 3.32 eV after annealing at 1000 ℃, suggesting electrically activated Al donors.