why 'beta' of transistor increases with temperature?

Can anyone explain why β of a transistor increases with temperature and base-emitter voltage decreases with increase in temperature?
Regards

It because of the fact that base transport factor(which constitute mobility and recombination lifetime) reduces with temperature, in turn causing decrease in base current, and therefore an increase in β.

I would attribute increased beta to the increase in thermal injection

BJT's are formed from doped semiconductors. Semiconductor properties can be quite sensitive to temperature. For a conductor, resistance increases with temperature. In a simple model, this can be thought of as due to the increased motion of the atomic cores that inhibit the flow of conduction electrons.

However, the resistance of a semiconductor decreases with temperature. To understand this fully requires some advanced knowledge, but is because though the atomic cores of the semiconducting material are moving about more, extra charge carriers are also being generated. The extra generation outweighs the increased motion of the atomic cores.

A reasonable explanation of this is given in an old book:
"Analogue and Digital Electronics", Ahmed and Spreadbury, Cambridge University Press (1984)

Quite informative theory at

http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/transtemp.html