562015-03-24 , 法政大学大学院理工学・工学研究科
The origins of low resistivity in H ion-implanted ZnO bulk single crystals are studied by Rutherford backscattering spectroscopy (RBS), photoluminescence (PL), Nuclear reaction analysis (NRA), elastic recoil detection analysis (ERDA), and Van der Pauw methods. The resistivity decreases from ~103 Ωcm for un implanted ZnO to 6.5 Ωcm for as-implanted, 2.3 × 10-1 Ωcm for 200 ℃ annealed, and 3.2× 10-1 Ωcm for 400 ℃ annealed samples. RBS measurements show that Zn interstitial as a shallow donor is not recognized in as-implanted samples. From photoluminescence measurements, the broad green band emission is observed in as-implanted samples. NRA measurements for as-implanted ZnO suggest the existence of the oxygen interstitial. The origins of the low resistivity in the as-implanted sample are attributed to both the H interstitial as a shallow donor and complex donor between H and disordered O. In 200 ℃ and 400 ℃ annealed samples, hydrogen evaluated from ERDA measurements is observed more than that in as-implanted samples, suggesting that hydrogen is out diffused by annealing. From EPR measurements, the oxygen vacancy of + charge state (Vo+) is observed in as-implanted samples. The activation energy of as-implanted, 200 ℃ annealed, and 400 ℃ annealed samples estimated from the temperature dependence of carrier concentration lies between 29 meV and 23 meV, suggesting the existence of H interstitial as a shallow donor level.