A doped semiconductor has impurity levels 20 meV below the conduction band. Is the material n-type or p-type? What is the wavelength of light so that the electron of impurity level is just able to jump into conduction band?
Use `h=6.63xx10^(-34)Js, c=3xx10^(8)m//s`.

Explanation

Here, `E=20 meV=20xx10^(-3)xx1.6xx10^(-19)J`
`=20xx1.6xx10^(-22)J`
When electron from impurity levels, due to excitation, jumps to conduction band, increases the number density of electrons in conduction band as compared to number density of holes in valence band. Thus the material is n-type.
`lambda_(max)=(hc)/E=((6.63xx10^(-34))xx(3xx10^(8)))/(20xx1.6xx10^(-22))`
`=6.22xx10^(-5)m`