I've learnt that under the forward biased condition in PN junction, the diffusion current increases slowly and after surpassing the cut-in voltage, the diffusion current increases exponentially, and under reverse biased condition, the diffusion current approaches zero. In either of the conditions, the drift current is said to remain almost constant.
Why is it so? Why is the drift current independent of the electric field (by the battery)? Why did my textbook emphasized on the word "almost" when talking about the drift current to be constant? Shouldn't the movement of minority charge carriers (drift current) increase under the reverse biased condition in PN junction?