Nitrogen doping effect on phase change optical disks

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 7 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 x 10(5) overwrite cycles at lambda=790 nm, N A=0.50 and using the pit position modulation (PPM) recording method where the minimum bit length is 0.87 mu m.