Ion Induced Damage and their Annealing in LiTaO 3 Single Crystal
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SULTS AND DISCUSSION Radiation damage in the as - implanted sample Figure. 1 shows the 2 Mev He ion RBS-channeling spectra taken along the c-axis on the implanted area and on the un-implanted area (virgin spectrum) before annealing. As a comparison, spectrum taken along random direction (random spectrum) is also included. For the samples implanted with high doses (1.2x10 15 /cm 2 and above), the backscattering yield has reached random level. TEM diffraction pattern taken on the sample implanted with 2x10 16 /cm 2 of oxygen ions shows a diffused ring, indicating that the implanted layer was amorphized. The interface (around channel 195) between the amorphized layer and the underlying portion of the sample is quite sharp as indicated by the sharp drop in the channeling yield. The thickness of the amorphized layer increases with the implantation dose, to about 190 mn for the dose of 2xl0 16 /cm 2 . On the other hand, for the samples implanted with low doses ( 1x10 14 /cm 2 and 6x10 14 /cm 2 ), the backscattering yield is much lower than the random level, indicating that only little damage is present after implantation. From the TRIM calculation, for the LiTaO 3 implanted with 100 keV oxygen ions, the DPA (displacement per atom) in the center region of the implanted layer is higher than in the near surface region. It is expected that the damage density should be lower near the surface region. This appears to be the case in the sample implanted with 6x10 14 /cm 2 oxygen, as evidenced by the channeling yield (Figure 1). However, this is not the case for the sample
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Chanmel Fig. 1. 2 MeV He ion RBS-channeling spectra. (X) Random spectrum. Aligned spectium taken before annealing(as-imp.spectrum) on sample implanted with ( * ) 2x10 16 /cm 2 oxygen ions; (0) 6x1015 /cm 2 oxygen ions; ( 0) 1.2x1015 /cm 2 oxygen ions; ( ) 6x10 14 /cm 2 oxygen ions; (+) lxlO14 /cm 2 oxygen ions; and ( v ) Aligned spectrum taken on virgin sample ( virgin spectrum).
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implanted with a dose of IxI0 14 /cm 2 . In this sample, the damage density near the surface region is much higher than that in the center region as the RBS-channeling spectrum shows lower counts in the center region and much higher counts at the surface (Figure. 1). It seems that the lattice has the ability of self-heeling when the damage density is low. Annealing of partially damaged samples RBS-channeling spectra taken on partially damaged samples before and after annealing are 14 0 presented in Fig.2. After annealing at 550 C for 30 min, the backscattering counts of both lx10 14 2 2 /cm and 6x10 /cm implanted samples has reduced to virgin level, indicating complete recovery of the crystalline structure. LiTaO3 single crystal has a Curie temperature around 6050C. Such low Tc may prohibit the application of ion implantation for doping of impurities in LiTaO
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