Question

(i). In an unbiased p-n junction, why holes diffuse from the p- region to n- region?

(ii). A p-n junction is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 600 nm?

Answer 1

(i). In an unbiased p-n junction, 

Holes diffuse from the p- region to n- region because hole concentration in p-region is more as compared to n- region.

(ii). Energy, 

E = \(\frac{hc}{\lambda}\)

= \(\frac{6.6\times10^{-34}\times 3 \times 10^8}{600\times 10{-9}\times 10^{-19}}\)eV

= 2.06 eV

As E< Eg (2.8 eV),

So p-n junction cannot detect the radiation of given wavelength.