a) Define Define the quantum quantum efficiency efficiency and and the responsiv responsivity ity of a photodete photodetector. ctor.Deriv Derivee an expression for the responsivity of an intrinsic photodetector in terms of the quantum efficiency of the device and the wavelength of the incident radiation. Determine the wavelength at which the quantum efficiency and the responsivity are equal. b) A silicon silicon p-i-n p-i-n photodiode photodiode with an area area of 1.5 mm2 mm2 is to be used used in conjunction conjunction with a load resistor of 100 Ω. If the requirement for the device is a fast response time, estimate the thickness of the intrinsic region that should be provided. It may be assumed that the permittivity for silicon is 1.04 x 10-10 Fm-1 and that the electron saturation velocity is 107 ms-1 c) A silicon silicon p-i-n p-i-n photodiode photodiode with active active dimension dimensionss 10 μm. has a specif specific ic 10 -1 detectivity of 7 x 10 m HzW when operating at a wavelength of 0.85 μm. The device quantum efficiency at this wavelength is 64%. Assuming that it is the dominant noise source, calculate the dark current over a 1 Hz bandwidth in the device. d) Compare Compare and contrast contrast the structure structure and performa performance nce characteris characteristics tics of germaniu germanium m and III—V semiconductor alloy APDs for operation in the wavelength range 1.1 to 1.6 μm. e) Discuss Discuss the operati operation on of the silicon silicon RAPD, RAPD, describi describing ng how it differ differss from the p-i-n photodiode. Outline the advantages and drawbacks with the use of the RAPD as a detector for optical fiber communications.
f) Outline the reasons for the adoption of the materials and devices used for photo detection in optical fiber communications Discuss in detail the p-i-n photodiode with regard to performance and compatibility requirements in photo detector. g) A p-i-n photodiode ceases to operate when photons with energy greater than 0.886 eV are incident upon it; of which material is it fabricated? h) The specific detectivity of a wide area silicon photodiode at its operating wavelength is 1011m Hz W-1 . Estimate the smallest detectable signal power at this wavelength when the sensitive area of the-device is 25 mm2 and the signal bandwidth is I kHz. i) An APD with a multiplication factor of 20 operates at a wavelength of 1.5 μm. Calculate the quantum efficiency and the output photocurrent from the device if its responsivity at this wavelength is 0.6 A /W and 1010 photons of wavelength 1.5 μm are incident upon it per second. j) An lnGaAsP heterojunction phototransistor has a common emitter current gain of 170 when operating at a wavelength of 1.3 μm with an incident optical power of 80 μW. The base collector quantum efficiency at this wavelength is 65%. Estimate the collector current in the device. k) Describe the basic detection process in a photoconductive detector. The maximum 3 dB bandwidth allowed by an InGaAs photoconductive detector 380MHz when the electron transit time through the device is 7. 6 ps. Calculate the photocurrent obtained from the device when 10 μW of optical power at a wavelength of 1.32 μm is incident upon it and the device quantum efficiency is 75%. l) An APD has a-quantum efficiency of 45% at 0.85 μm. When illuminated with radiation wavelength it produces an output photocurrent of 10 μA after avalanche gain multiplication factor of 250. Calculate the received optical power to the device. How many photons per second does this correspond to? m) A germanium photodiode incorporated into an optical fiber receiver working at a wavelength of 1 .55 μm has a dark current of 500 nA at the operating temperature. the incident optical power at this wavelength is 10-6 W and the responsivity of is 0.6 A /W , shot noise dominates in the receiver. Determine the SNR in dB at the receiver when the post detection bandwidth is 100 MHz.
