Question
Consider a situation in which reverse biased current of a particular $P-N$ junction increases when it is exposed to a light of wavelength $\le 621\, {nm}$. During this process, enhancement in carrier concentration takes place due to generation of hole-electron pairs. The value of band gap is nearly. (In ${eV}$)

Answer

Band gap $=\frac{h c}{\lambda_{0}}$

Where $\lambda_{0}=$ threshold wavelength

Band gap $=\frac{1242\, {ev}-\,{nm}}{621\, {nm}}=2\, {ev}$

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