P/N Junctions and Avalanche Photodiodes (APDs) Quiz Answers

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P/N Junctions and Avalanche Photodiodes (APDs) Quiz Answers

Question 1)
Using Shockley’s lucky electron thoery, consider a conventional APD made of a GaAs p-i-n junction. The device was illuminated on the p-side with an incident light whose energy was 1.42 eV and power was 1.0 μW. Assume the quantum efficiency η=0.8 and note the charge on the electron, q=1.6×10⁻¹⁹ C, and ℎ  ,Planck’s constant, is 6.63 × 1 0^{− 34}  m ² kg/s.

If the output current was 10 μA, what is the gain? Your answer should be unitless.

Answer: 16

Question 5)
Consider a conventional APD made of a GaAs p-i-n junction. The device was illuminated on the p-side with an incident light whose energy was 1.42 eV and power was 1.0 μW. Assume the quantum efficiency η=0.8 and note the charge on the electron, q=1.6×10⁻¹⁹ C, and ℎ, Planck’s constant, is 6.63×10⁻³⁴ m²kg/s.

The reverse bias voltage is 5 V. For simplicity, assume that the electric field is zero in p- and n-type regions and that the applied voltage and the built-in potential produce a constant electric field throughout the intrinsic layer whose thickness was 1.0μm.

• Useful parameters:  threshold energy for impact ionization Eth = 3.0eV
• ​electron effective mass m_e=0.067mo, electron rest mass mo​=9.11×10⁻³¹kg
• Inverse of phonon scattering rate (relaxation time) τ=1.0×10⁻¹³ s
• Built-in potential V_bi ​ =1V. If this is less than the breakdown voltage value, enter 1. Otherwise, enter 0.

Answer: 1