In a photodiode, the conductivity increases when the material is exposed to light. It is found that conductivity changes only if the wavelength is less than 600 nm. What is the bandgap?
Question
In a photodiode, the conductivity increases when the material is exposed to light. It is found that conductivity changes only if the wavelength is less than 600 nm. What is the bandgap?
Solution
The bandgap of a material in a photodiode can be calculated using the formula:
E = hc/λ
where: E is the energy of the photon (which is equal to the bandgap for the minimum energy required to create a charge carrier), h is Planck's constant (6.626 x 10^-34 Joule seconds), c is the speed of light (3.00 x 10^8 meters/second), and λ is the wavelength of the light.
Given that the wavelength (λ) that causes a change in conductivity is 600 nm or 600 x 10^-9 meters, we can substitute these values into the formula:
E = (6.626 x 10^-34 J.s)(3.00 x 10^8 m/s) / (600 x 10^-9 m) E = 3.31 x 10^-19 Joules
However, the energy of a photon is usually expressed in electron volts (eV). To convert from Joules to eV, use the conversion factor 1 eV = 1.602 x 10^-19 Joules:
E = (3.31 x 10^-19 Joules) / (1.602 x 10^-19 Joules/eV) E = 2.07 eV
Therefore, the bandgap of the material in the photodiode is approximately 2.07 eV.
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