Plot a graph showing variation of current versus voltage for the material GaAs. Explain the graph.

The variation of current versus voltage for a material GaAs is shown below,

According to Ohm's Law, the current passing through a conductor is directly proportional to the voltage applied across it.

Thus V ∝ I

V ​= IR

R is the resistance of the conductor.

Hence for Ohm's law to obeyed, the slope of I vs V curve is constant and positive. 

Hence region BC obeys Ohm's law.

For R to be negative, slope of I vs V curve should be negative, which is there for region DE.