Question
Physics Question on Photoelectric Effect
In a p - type semiconductor the donor level is at 50meV above the valence band. To produce one electron, the maximum wavelength of light photon required is (Planck's constant, h=6.6×10−34Js and speed of light in vacuum, c=3×108ms−1 )
0.0248μm
0.248μm
2.48μm
24.8μm
24.8μm
Solution
Given,
p -type semiconductor donor energy level,
E=50meV=50×10−3×1.6×10−19V
Planck's constant, h=6.6×10−34Js
speed of light in vacuum, c=3×108m/s
Now, for the maximum wavelength of light photon's required (p).
According to the Planck's quantum theory,
∴E=hv
⇒E=λhc
[∵v=λc]
Putting the given values, we get
50×10−3×1.6×10−19=λ6.6×10−34×3×108
λ=50×10−3×1.6×10−196.6×10−34×3×108
=5×16×10−226.6×3×10−34×108=5×166.6×3×10−4
=2.475×10−5m
or λ=24.75×10−6=24.75μm
Hence. the maximum wavelength of light photon required is 24.8μm