Solution Manual For Fundamentals of Photonics,ELECTRONIC 11241SM-Ch5.pdf

Solutions Manual for Optoelectronics and Photonics: Principles and Practices S.O. Kasap 5 . 1 23 April 2001 Chapter 5 5.1 Bandgap and photodetection a Determine the maximum value of the energy gap which a semiconductor, used as a photoconductor, can have if it is to be sensitive to yellow light (600 nm). b A photodetector whose area is 5×10-2 cm2 is irradiated with yellow light whose intensity is 2 mW cm−2 . Assuming that each photon generates one electron-hole pair, calculate the number of pairs generated per second. c From the known energy gap of the semiconductor GaAs (Eg = 1.42 eV), calculate the primary wavelength of photons emitted from this crystal as a result of electron-hole recombination. Is this wavelength in the visible? d Will a silicon photodetector be sensitive to the radiation from a GaAs laser? Why? Solution a Given, λ = 600 nm, we need Eph = hυ = Eg so that, Eg = hc/λ = (6.626×10-34 J s)(3×108 m s-1)/(600×10-9 m) = 2.07 eV b A = 5×10-2 cm2 and Ilight = 20×10-3 W/cm2 . The received power is P = AIlight = (5×10-2 cm2 )(20×10-3 W/cm2 ) = 10-3 W Nph = number of photons arriving per second = P/Eph = (10-3 W)/(2.07×1.60218 ×10-19 J/eV) = 2.9787×1015 Photons s-1.