Lateral spreading of dopants

The short-channel effect is closely related to the lateral spreading of dopants from the source and drain areas to the gate region, which is contributed by two effects ... 

Researchers in microelectronics have found that a slight scratch on the surface of gallium arsenide causes a zinc dopant to diffuse into the arsenide. Apparently, this occurs because the scratch increases crystal defects and hence the local diffusion coefficient. When these devices are later baked at 850 °C, the small pulse may spread, for its diffusion coefficient at this high temperature is about 10 cm /sec. If it spreads enough to increase the zinc concentration to 10 percent of the maximum at... 

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