Bandgap and photodetection Determine the maximum value of the energy gap that a

Question

Bandgap and photodetection Determine the maximum value of the energy gap that a semiconductor, used as a photoconductor, can have if it is to be sensitive to yellow light (600nm) A photdetector whose area is 5 times 10-2 cm2 is irradiated with yellow light whose intensity is 2mW cm-2. Assuming that each photon generates one electron-hole pair, calculate the number of pairs generated per second. From the know energy gap of the semiconductor GaAs (Eg = 1. 42eV), calculate the primary wavelength of photons emitted from this crystal as a result of electron-hole recombination. Is the above wavelength visible? Will a silicon photodetector be sensitive to the radiation from a GaAs laser? Why?

Explanation / Answer

a.Eg = hf = hc/λ 

= 1.24 / 0.6 = 2.066 eV

b. intensity = E/A

E = IA = 0.002 X 0.05 =  10^-4 J

nX 2.066 X 1.6 X 10^-19 J = 10^-4

n= 3.02 X 10^14 photons.

hence same no po electron hole pairs are created.

c. λ = 1.24 /Eg μm = 873.23 nm

d . no it is not in visible range.

e. Eg of silicon = 1.122 eV .  yes a silicon photodetector can be a photodetector because , as Si is an indirect band gap material , some energy of incient photon is lost which makes its energy equal to 1.122 and hence it is sensitivs.

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