You are given three semiconductors —A, B and C with respective bandgaps of 3 eV, 2 eV and 1 eV for use in a photodetector to detect λ = 1400 nm. Select the suitable semiconductor. Give reasons.

Solution

Given that,
Energy band gap of semiconductors are 3 eV, 2 eV and 1 eV respectively.
Wavelength, λ = 1400 nm

Energy of the photon,

E = \frac{hc}{λ}

= \frac{6.63 \times 10^{- 34} \times 3 \times 10^{8}}{1400 \times 10^{- 9}} J = \frac{6.63 \times 10^{- 34} \times 3 \times 10^{8}}{1400 \times 10^{- 9} \times 1.6 \times 10^{- 19}} eV = 0.89 eV

E_{g}

has to be less than hv or

\frac{hc}{λ} .

None of the semiconductor is suitable since E_g for 1400 nm is 0.89 eV which is less than the band gap E_g of the given semiconductors.

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