Excess Noise Factor
APD excess noise vs gain — McIntyre model for different semiconductor materials.
Excess Noise F
3.9502
Noise Figure 10·log₁₀F
5.97 dB
Shot-Limited SNR vs p-i-n
×0.503
amplitude ratio 1/√F
Excess Noise Index x
0.298
datasheet form F = M^x
F(M) = k·M + (1 − k)·(2 − 1/M) [McIntyre 1966]
Si: k = 0.02 (range 0.02–0.05), InGaAs/InP: k = 0.5 (range 0.5–0.7), Ge: k = 0.85 (range 0.7–1)
x = ln F / ln M, so F = M^x holds exactly at the entered gain only
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
McIntyre's F for a uniform field and pure injection of the more ionising carrier, with the k presets of the avalanche-gain page. The SNR chart is shot-noise limited (no amplifier noise), and x = ln F/ln M matches the datasheet form F = M^x only at the entered gain. Local model; dead space in thin (sub-µm) multiplication layers lowers F.
- McIntyre R. J. (1966). Multiplication noise in uniform avalanche diodes. IEEE Trans. Electron Devices ED-13, 164–168. F = kM + (1 − k)(2 − 1/M). doi:10.1109/T-ED.1966.15651
- Agrawal G. P. (2010). Fiber-Optic Communication Systems, 4th ed. Wiley. §4.4 (APD receiver noise, optimum gain) and Table 4.2 (k: Si 0.02–0.05, InGaAs 0.5–0.7, Ge 0.7–1.0). doi:10.1002/9780470918524
- Excelitas Technologies. C30902EH and C30921EH avalanche photodiodes, datasheet Rev. 2022.02. k_eff = 0.02; V_br = 225 V at 22 °C, 0.7 V/°C; M = 150; dark current 7 nA. excelitas.com