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The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap in (eV) for the semiconductor is

  • Option 1)

    0.5 eV

  • Option 2)

    0.7 eV

  • Option 3)

    1.1 eV

  • Option 4)

    2.5 eV


Answers (1)

As we learnt in

Photo diode -

A special type of photo detector.

- wherein

By measuring the change in the conductance of the semicondutors one can measure the intensity of the optical signal


 Electrical conductivity increases when more electrons jump from valence band to conductioin band. Hence the light must provide energy equal to or more than band gap.

Band gap \frac{hc}{\lambda}=\frac{12400}{24800}=0.5\ eV

Correct option is 1.


Option 1)

0.5 eV

This is the correct option.

Option 2)

0.7 eV

This is an incorrect option.

Option 3)

1.1 eV

This is an incorrect option.

Option 4)

2.5 eV

This is an incorrect option.

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