First slide

Opto electronic juction devices

Question

A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV. It can detect a signal of wavelength

Moderate

A

6000 $\overset{o}{A}$
B

4000 nm
C

6000 nm
D

4000 $\overset{o}{A}$

Solution

Only signals having wavelength less than threshold wavelength will be detected.
$Energy E = hv = h \frac{c}{λ} \Rightarrow λ = \frac{hc}{E}$
Substituting the values of h, c and E in the above equation
$λ = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{2.5 \times 1.6 \times 10^{- 19}} = 5000 \overset{0}{A} As 4000 \overset{0}{A} < 5000 \overset{0}{A}$

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