Question: Q. 2. Mention the important considerations required while fabricating a $p-n$ junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED if it is required to emit light in the visible range?
R [Delhi I, II, III 2013]
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Solution:
Ans. (i) It is a heavily doped $p-n$ junction diode.
(ii) The reverse breakdown voltages of LEDs are very low.
(iii) The semiconductor used for fabrication of visible LEDs must at least have a band gap of $1.8 \mathrm{eV}$.
(Any two) $1 / 2+1 / 2$
The order of band gap is about $3 \mathrm{eV}$ to $1.8 \mathrm{eV} . \quad \mathbf{1}$
[CBSE Marking Scheme 2013]
