Question

EB 2 0 W Active Saturation 0 CB 0 W Cutoff Inverted

These are the four modes for the bipolar junction transistors (PNP type).

FOR THE ACTIVE CASE: I am having trouble understanding why the minority carriers (electrons) increase in the emitter region as you approach the depletion region. Similarly, why is there so much minority carriers in the base (and why does it decrease as it approaches the base collector junction). Also why are the minority carriers (n) in the collector region initially very low, the increases?

Can you explain how the minority carrier distributions are impacted by the applied voltages?

Answer 1

The BJT has three separately doped regions and two p-n junctions, which are sufficiently close together that they interact with each other. Let us consider the ACTIVE case - In this B-E junction is forward biased and B-C junction is reversed biased. Large concentration of minority carriers to appear in the base near the B-E junction due to injection of electrons from the emitter. A concentration gradient will be created within the base region in terms of minority carriers, this will generate a diffusion current through the base The B-C junction is reverse biased, so majority carriers (holes) from the base do not enter the collector in large concentrations: however, the minority carriers that diffuse to the B-C junction will be readily swept across. If the base region is very narrow, comparable to electrons diffusion lengths, few electrons will be lost through recombination \r\n The MINORITY carrier concentration will look like - The number of electrons per unit