光电子学与光子学原理与实践第五章答案.pdf

Preliminary Solutions to Problems and Questions Chapter 5 Note: Printing errors and corrections are indicated in dark red in Questions 5.4, 5.21 and 5.32. 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 (600nm). -2 2 (b) A photodetector whose area is 510 cm is irradiated with yellow light whose intensity is 2 –2 mW cm . 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,  = 600 nm, we need E = h = E so that, ph g -34 8 -1 -9 Eg = hc/ = (6.62610 J s)(310 m s )/(60010 m) = 2.07 eV -2 2 -3 2 (b) A = 510 cm and Ilight = 2010 W/cm . The received optical power is -2 2 -3 2 -3 P = AI = (510 cm )(2010 W/cm ) = 10 W o light and N = number of photons arriving per second = P /E ph o ph -3