CBSE Class 12 · 2016 · All India · SemiconductorsShort Answer

(i) During junction formation the two processes are diffusion of majority carriers across the junction and drift of minority carriers under the junction field; equilibrium is reached when these balance.
(ii) In a full-wave rectifier the ac is applied to the primary of a centre-tapped transformer; each diode is connected to one end of the secondary with the load between the centre tap and the junction of the diodes.
In one half-cycle diode $D_1$ is forward biased and conducts; in the next half-cycle $D_2$ conducts.
In both cases the current flows through the load in the same direction, so the output is unidirectional for both halves of the input.
$\boxed{\text{Diffusion \& drift; two diodes conduct alternately, same load direction.}}$