CBSE Class 12 · 2006 · All India · SemiconductorsShort Answer

(i) In forward bias the p-side is connected to the positive terminal and the n-side to the negative terminal; the applied field opposes the barrier field, the depletion layer narrows, and a large forward current flows once the knee voltage is crossed.
(ii) In reverse bias the p-side is negative and the n-side positive; the barrier widens and only a tiny minority-carrier current flows.
Half-wave rectifier: the ac source feeds a diode in series with a load $R_L$. During the half-cycle that forward biases the diode it conducts and gives an output across $R_L$; during the other half-cycle it is reverse biased and blocks current, so the output is unidirectional pulsating dc.
$\boxed{\text{Diode conducts one half-cycle}\Rightarrow \text{half-wave rectification.}}$