First slide

Diodes

Question

Three photodiodes $D_{1}, D_{2} a n d D_{3}$ are made of semiconductors having band gaps of 2.5 eV, 2 eV and 3 eV respectively. Which one will be able to detect of wavelength of $6000 \overset{o}{A}$

Easy

A

$D_{1}$
B

$D_{2}$
C

$D_{3}$
D

None

Solution

$F o r t h e i n c i d e n t r a d i a t i o n t o b e d e t e c t e d b y t h e p h o t o d i o d e, e n e r g y o f i n c i d e n t r a d i a t i o n s h o u l d b e g r e a t e r t h a n t h e b a n d g a p .$
$E n e r g y o f p h o t o n = E = \frac{h c}{e λ} = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{1.6 \times 10^{- 19} \times 6 \times 10^{- 7}} = 2.06 e V$
$T h i s i s t r u e o n l y f o r D_{2} .$

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