Beta-NMR study on impurity diffusion in semiconductors.

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The beta-NMR measurements of the boron impurity in germanium were performed. The obtained results are as follows. Three resonances were found : a sharp resonance and a broad one around the Larmor frequency, a resonance at vqSplit=190 kHz. In the same manner as silicon, these three resonances were expected to correspond to the substitutional site (Bs), the site which shows polycrystal pattern (Bx), and the <111> axial symmetrical site (Bns), respectively. While the fraction of Bns is almost constant of 30 % below the temperature of 250 K, above 300 K the resonance disappears. This disappearance is also similar with the case of silicon, i.e., the spin-lattice relaxation should be caused by the fluctuation of the internal field due to the atomic jumps. The temperature dependence of the Bs+Bx was slightly different to the silicon case. Around the room temperature it decreases and makes a depression. One explanation for it may be that the chance for the interaction of Bs or Bx with the vacancy created by the implantation increases with the temperature, and it follows destruction of the polarization.In order to confirm the model of the atomic jump, the temperature dependence of the fractions of each site were measured under the different external magnetic fields. As a result, the temperature at which the NMR signal disappears agreed with the expected value by our model. This supports the validity of the atomic jump model.The nitrogen impurity in the compound semiconductor TiO2 and ZnO was also investigated. The electric field gradient at the nitrogen impurity in ZnO was measured. The nitrogen impurity in TiO2 locates at oxygen substitutional site and interstitial lattice site. While the substitutional nitrogen seems to be immobile, the defect around the substitutional nitrogen and the interstitial nitrogen seems to be mobile thermally.