Nitrogen Doping Effect on Phase Change Optical Disks

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Abstract
The nitrogen doping effect on the Ge–Sb–Te recording layer was quantitatively examined. We succeeded in the quantitative analysis of the nitrogen concentration in the Ge–Sb–Te–(N) recording layer by secondary ion mass spectrometry (SIMS) observation. The nitrogen concentration could be finely controlled at a high deposition rate of 4.7 nm/s. The addition of a small amount of nitrogen remarkably improved the overwrite cycle numbers. We found that the most suitable nitrogen concentration was from 2 to 3 at%. We proposed a model to explain the nitrogen atom function in the recording layer. The nitrogen atoms produced nitrides, which are condensed near the grain boundaries of Ge–Sb–Te microcrystals. This resulted in the formation of very thin wrappings, which wrap the crystal grain in a manner similar to that of the peel of a peach and suppressed the micro-material flow. We achieved 8×105 overwrite cycles at λ=790 nm, N A=0.50 and using the pit position modulation (PPM) recording method where the minimum bit length is 0.87 µm.

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