You have two regions, A and B, of differently doped silicon, with the regions joined together to make a continuous silicon crystal. When the positive terminal of a battery is connected to region \(\mathrm{A}\) and the negative terminal is connected to region B, no charge carriers flow. When the terminal connections are switched, charge carriers flow.

(a) When there is a current, in which direction-A to B or B to A-do the positive charge carriers move?

(b) In which direction do the electrons move?

(c) Which region is \(p\)-type and which is \(n\)-type?

(d) Which region may contain boron, and which may contain phosphorus?