Question

An LED is constructed from a pn junction based on a certain semi-conducting material whose energy gap is 1.9 eV. Then the wavelength of the emitted light is

• A. 6.5 $\times$ ${10}^{-7}$ m
• B. 2.9 $\times$ ${10}^{-9}$ m
• C. 9.1 $\times$ ${10}^{-5}$ m
• D. 1.6 $\times$ ${10}^{-8}$ m

Answer 1

The correct option is A

6.5 $\times$ ${10}^{-7}$ m

$E_g=\frac{hc}{\lambda }\Rightarrow \lambda =\frac{hc}{E_g}=\frac{1240}{1.9}eVnm\approx 650nm$