is proportional to the electric field for all values of electric field

is independent of the electric field

increases at low values of electric field and decreases at high values of electric field exhibiting negative differential resistance.

increases linearly with electric field at low values of electric field and gradually saturates at higher values of electric field.

both the junctions are reverse biased

base-emitter junction is reverse biased and base-collector junction is forward biased.

base-emitter junction is forward biased and base-collector junction reverse biased

both the junctions are forward biased

tunneling of charge carriers across the junction

thermo ionic emission

diffusion of charge carriers across the junction

hopping of charge carriers across the junction

C_J $$\propto$$ V_R

C_J $$\propto$$ V_R^-1

C_J $$\propto$$ V_R^-1/2

C_J $$\propto$$ V_R^-1/3