Re: why MOBILITY of HOLE is less than ELECTRON?

Hello, Durga.

Your question is an excellent one – it made me go right back to the basics 
of how we describe electrons and holes in semiconductors.

The short answer is that conduction electrons live in the conduction band 
and holes live in the valence band, and the behavior of electrons in each 
of these bands is different.   One of the things that is different is the 
mobility – so it makes sense that conduction electron mobilities are 
different than the hole mobilities, where the electrons that have to get 
out of the way of the hole are in a different band.

A longer answer would wind up being too long – there are just too many 
issues involved in describing why different electronic bands behave 
differently.  Even the concept of a “energy band” could take a long time 
to explain, so I’ll have to assume that if you’ve been introduced to holes 
and mobility, you can access your own sources to flesh out the details.  
Good luck.