Can refractive index of a substance be increased?

[aditya23456]

or is it possible to create a material with very high refractive index(order of 100's or more)

 

[DrDu]

Yes, the index of refraction becomes very high near an absorption line. If the absorption line is very narrow, the index of refraction becomes very high. There are other possibilities as well, e.g. using nonlinear optics the refractive index at one frequency can be tuned by a laser operating at another frequency.
See also
http://en.wikipedia.org/wiki/Slow_light