Silicon Photodiode

Si photodiode parameters: bandgap, QE, responsivity, dark current, and spectral response.

Temperature (K)Depletion Width W (μm)Diffusion Length L (μm, 0 = none)Active Area (mm²)Surface ReflectivityGeneration Lifetime τ_g (ms)

Results

Bandgap E_g

1.1263 eV

h·c/E_g = 1101 nm

Peak Responsivity

0.592 A/W

at 840 nm

QE @ 700 nm

94.3%

Responsivity @ 900 nm

0.563 A/W

QE 77.6%

Dark Current (generation)

8.57 pA

Junction Capacitance

10.54 pF

Spectral Response (absorption at 300 K)

QE vs Depletion Width

Dark Current vs Temperature

Formulas

E_g(T) = 1.170 − 4.73×10⁻⁴·T²/(T + 636) eV (Varshni, Sze)

η(λ) = (1 − R)·[1 − e^(−αW)/(1 + αL)] (Gärtner: depletion region plus diffusion from the substrate)

ℛ(λ) = η·q·λ/(h·c)

I_dark = q·n_i·W·A/τ_g, n_i(300 K) = 9.65×10⁹ cm⁻³ ∝ T^(3/2)·e^(−E_g/2kT)

C_j = ε₀·11.9·A/W

α(λ) is Green's 2008 table for silicon at 300 K at every temperature: the band-gap shift moves the long-wavelength edge by about 0.25 nm/K, which this page does not apply. Silicon is an indirect absorber, so some response remains beyond h·c/E_g.

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

QE from Green's 300 K silicon absorption with Gärtner's depletion-plus-diffusion collection; the absorption edge does not shift with temperature. Dark current is depletion generation q·n_i·W·A/τ_g only (no diffusion or surface leakage); n_i = 9.65e9 cm⁻³ at 300 K scaled with T^(3/2) and the Varshni gap. Capacitance is a parallel plate with ε_r = 11.9. τ_g is an independent input, not tied to L: a midgap trap would give τ_g ≈ 2τ_r = 2L²/D, far shorter than 1 ms.

Green M. A. (2008). Self-consistent optical parameters of intrinsic silicon at 300 K including temperature coefficients. Sol. Energy Mater. Sol. Cells 92, 1305–1310. Table 1, n and k at 250–1450 nm (α = 4πk/λ). doi:10.1016/j.solmat.2008.06.009
Gärtner W. W. (1959). Depletion-layer photoeffects in semiconductors. Phys. Rev. 116, 84–87. Collection efficiency 1 − e^(−αW)/(1 + αL). doi:10.1103/PhysRev.116.84
Altermatt P. P., Schenk A., Geelhaar F., Heiser G. (2003). Reassessment of the intrinsic carrier density in crystalline silicon in view of band-gap narrowing. J. Appl. Phys. 93, 1598–1604. n_i = 9.65e9 cm⁻³ at 300 K. doi:10.1063/1.1529297
Sze S. M., Ng K. K. (2007). Physics of Semiconductor Devices, 3rd ed. Wiley. Generation current q·n_i·W/τ_g, n_i(T), Varshni E_g(T) coefficients for Si, ε_r = 11.9. doi:10.1002/0470068329

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