Full interactive photodiode datasheet
Change the reverse bias, temperature, wavelength or load, and the curves and the spec table recalculate from device physics. Both devices are fictional examples built from textbook physics.
Device model
- Responsivity R
- 0.641A/W
- Dark current ID
- 148pA
- Capacitance Cj
- 14.1pF
- Bandwidth f−3 dB
- 8.09MHz
- Shot noise, dark current6.9 × 10⁻¹⁵ A/√Hz
- Johnson noise, shunt4.0 × 10⁻¹⁵ A/√Hz
- Johnson noise, 1.00 kΩ load4.1 × 10⁻¹² A/√Hz
Dark current vs reverse bias
Junction capacitance vs reverse bias
Spectral responsivity
Frequency response
| Parameter | Conditions | Value |
|---|---|---|
| Responsivity Rλ = 850 nm, VR = 10.0 V | λ = 850 nm, VR = 10.0 V | 0.641 A/W |
| Quantum efficiency ηλ = 850 nm, VR = 10.0 V | λ = 850 nm, VR = 10.0 V | 93.5 % |
| Dark current IDVR = 10.0 V, T = 25 °C | VR = 10.0 V, T = 25 °C | 148 pA |
| Shunt resistance RshV = ±10 mV, T = 25 °C | V = ±10 mV, T = 25 °C | 1.02 GΩ |
| Junction capacitance CjVR = 10.0 V, f = 1 MHz | VR = 10.0 V, f = 1 MHz | 14.1 pF |
| Depletion width WVR = 10.0 V | VR = 10.0 V | 36.8 µm |
| Bandwidth f−3 dBVR = 10.0 V, RL = 1.00 kΩ, λ = 850 nm | VR = 10.0 V, RL = 1.00 kΩ, λ = 850 nm | 8.09 MHz |
| Rise time, 10 % to 90 % trVR = 10.0 V, RL = 1.00 kΩ, λ = 850 nm | VR = 10.0 V, RL = 1.00 kΩ, λ = 850 nm | 60.7 ns |
| RC limit fRCRL + Rs = 1.01 kΩ | RL + Rs = 1.01 kΩ | 11.2 MHz |
| Transit limit ftrVR = 10.0 V | VR = 10.0 V | 138 MHz |
| Diffusion tail, share of signal pdiffλ = 850 nm, VR = 10.0 V, below 1.25 MHz | λ = 850 nm, VR = 10.0 V, below 1.25 MHz | 13.0 % |
| NEP, diode alone NEPλ = 850 nm, VR = 10.0 V, T = 25 °C | λ = 850 nm, VR = 10.0 V, T = 25 °C | 1.24 × 10⁻¹⁴ W/√Hz |
| NEP with the load NEPRL = 1.00 kΩ at 25 °C | RL = 1.00 kΩ at 25 °C | 6.33 × 10⁻¹² W/√Hz |
| Specific detectivity D*Diode alone | Diode alone | 1.80 × 10¹³ cm·√Hz/W |
| Linear range, load-line limit PmaxRL = 1.00 kΩ, VR = 10.0 V, λ = 850 nm | RL = 1.00 kΩ, VR = 10.0 V, λ = 850 nm | > 10 mW |
| Breakdown voltage VBRIR = 10 µA, 25 °C | IR = 10 µA, 25 °C | 120 V |
| Active area A5.0 mm² active area | 5.0 mm² active area | 5.0 mm² |
Equation: R = η λ / 1239.84. = 0.935 × 850 / 1239.84. Result 0.641 A/W. 1239.84 is hc/q in eV nm, so λ goes in nanometers and R comes out in amps per watt.Equation: η = (1 − r) (ηfront + ηdrift + ηdiff). = (1 − 0.05) × (0.002 + 0.855 + 0.128). ηdrift ∝ 1 − e to the power (−α W), α = 533 cm⁻¹ at 850 nm, W = 36.8 µm. Result 93.5 %. Light absorbed inside the depletion width is collected at once. Carriers made below it diffuse in, and some recombine on the way.Equation: ID = M I0 2 to the power ((T − 25)/Td) (W/W0) (1 − e to the power (−VR/VT)) + VR/Rleak. = 1.0006 × 25.0 pA × 2 to the power ((25 − 25)/9) × 3.91 × 1.000 + 10.0 V / 200 GΩ. VT = kT/q = 25.7 mV, W = 36.8 µm, W0 = 9.42 µm. Result 148 pA. Generation current in the depleted volume, which doubles every 9 °C, times the gain M that creeps in before breakdown, plus surface leakage through Rleak.Equation: Rsh = 1 / (I0(T)/VT + 1/Rleak). = 1 / (25.0 pA / 25.7 mV + 1 / 200 GΩ). Result 1.02 GΩ. The slope of the dark current at 0 V: generation current over the thermal voltage, in parallel with the leakage resistor. It falls as the diode warms.Equation: Cj = C0 / (1 + VR/Vbi) to the power m. = 55.0 pF / (1 + 10.0 / 0.70) to the power (0.5). Result 14.1 pF. Abrupt junction, m = 0.5. The 300.0 µm layer is still not fully depleted at the 30 V rating, so Cj keeps falling with bias.Equation: W = εr ε0 A / Cj. = 11.7 × 8.854 pF/m × 5.00 mm² / 14.1 pF. Result 36.8 µm. The parallel-plate relation, solved for the plate gap.Equation: |H(f)| squared = D(f) / ((1 + (f/fRC) squared) (1 + (f/ftr) squared)) = 1/2. fRC = 11.2 MHz, ftr = 138 MHz, fD = 1.25 MHz, p = 13.0 %. D(f) = (1 + (1 − p) squared (f/fD) squared) / (1 + (f/fD) squared). Result 8.09 MHz. Solved numerically for the frequency where the response is down 3 dB. D(f) is the slow diffusion share rolling off first.Equation: tr = t(90 %) − t(10 %) of the step response. τRC = 14.2 ns, τtr = 1.15 ns, τD = 127 ns, p = 13.0 %. each τ = 1/(2π f) of its limit, poles in cascade. Result 60.7 ns. The single-pole rule, 0.35 over the bandwidth, would give 43.3 ns. The diffusion tail stretches the edge well past it.Equation: fRC = 1 / (2π (Rs + RL in parallel with Rsh) Cj). = 1 / (2π × 1.01 kΩ × 14.1 pF). Rs + RL in parallel with Rsh = 10.0 Ω + 1.00 kΩ in parallel with 1.02 GΩ. Result 11.2 MHz. The junction capacitance charging through the series and load resistance. The shunt resistance is so large that it barely counts.Equation: ftr ≈ 0.44 v / W. = 0.44 × 1.16 × 10⁶ cm/s / 36.8 µm. v = μE / (1 + μE/vsat), E = (VR + Vbi)/W = 2.91 kV/cm. Result 138 MHz. Holes are the slower carrier: μ = 450 cm²/V s, vsat = 1.0 × 10⁷ cm/s. The 0.44 assumes light absorbed evenly across W.Equation: pdiff = ηdiff / (ηfront + ηdrift + ηdiff). = 0.128 / (0.002 + 0.855 + 0.128). τD = x squared / (2D) = 127 ns, x = 17.1 µm, D = μ kT/q = 11.6 cm²/s. Result 13.0 %. Carriers made below the depletion region diffuse up slowly. This share of the signal arrives late and rolls off above fD = 1.25 MHz.Equation: NEP = square root of (2q ID + 4kT/Rsh) / R. = square root of (2q × 148 pA + 4kT / 1.02 GΩ) / 0.641 A/W. = 7.97 × 10⁻¹⁵ A/square root of Hz / 0.641 A/W. Result 1.24 × 10⁻¹⁴ W/√Hz. Shot noise of the dark current and Johnson noise of the shunt resistance, with the diode at 25 °C. The shot noise is the larger here.Equation: NEP = square root of (2q ID + 4kT/Rsh + 4kT0/RL) / R. = 4.06 × 10⁻¹² A/square root of Hz / 0.641 A/W. shot 6.9 × 10⁻¹⁵, shunt 4.0 × 10⁻¹⁵, load 4.1 × 10⁻¹² A/square root of Hz; T0 = 25 °C. Result 6.33 × 10⁻¹² W/√Hz. The load sits on the board at 25 °C. At 1.00 kΩ its Johnson noise is the largest term by far.Equation: D* = square root of A / NEP. = square root of (0.0500 cm²) / 1.24 × 10⁻¹⁴ W/square root of Hz. Result 1.80 × 10¹³ cm·√Hz/W. NEP scaled by the square root of the area, so parts of different sizes compare on one scale. Diode alone, without the load.Equation: Pmax = (VR + Vbi) / ((RL + Rs) R). = (10.0 V + 0.70 V) / ((1.00 kΩ + 10.0 Ω) × 0.641 A/W). Result 16.5 mW. Above this power the voltage across the load eats into the bias and the response compresses. The table lists anything over 10 mW as > 10 mW.Equation: M = 1 / (1 − (VR/VBR) to the power n). = 1 / (1 − (10.0 / 120) to the power (3)). Result 1.0006. VBR is a property of the device. The model uses it for the gain M that multiplies the dark current near breakdown; the bias stops at 30 V.Equation: Cj = εr ε0 A / W. = 11.7 × 8.854 pF/m × 5.00 mm² / 36.8 µm. Result 14.1 pF. Area is a design choice. Capacitance grows with it, so a part with twice the area has half the RC bandwidth.
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