PIN Photodetector
This structure requires a wide depletion region wherein absorption and generation can take place. In reverse bias the depletion extends across the whole intrinsic region.
Table showing a possible PIN layer sequence
| Repeats | Thickness/mm | Material | Ts/C | Dopant | Type | concentration/cm3 |
| 1 | 0.05 | GaAs | 601 | Silicon | n | 4.0E18 |
| 1 | 1.00 | GaAs | 596 | Silicon | n | 1.0E18 |
| 1 | 1.00 | GaAs | 600 | undoped | ||
| 1 | 1.00 | GaAs | 569 | Beryllium | p | 1.0E18 |
| 1 | 0.20 | GaAs | 577 | Beryllium | p | 4.0E18 |
| 1 | 500.00 | GaAs | p+ |
PIN
Photodiode circuit model
The figure shows and
equivalent circuit for a PIN photodiode, which is connected to an external load
feeding an amplifier. In this diagram, the photoconductive current has been
modelled as a current source, Is, whose magnitude depends on the incident
optical power. The constant current source, Id, models the dark current, that
is, the leakage current and any photoconductive current due to background
radiation. The shunt resistance, Rj, represents the slope of the reverse bias
characteristic, and the series reistance, Rs, is that of the bulk semiconductor
and the contact resistance. The load resistor, RL, shunts the total
diode capacitance, Cd, and this time constant usually limits the speed of
response.
Optical
Communications,Chapter 4 Photodiodes,page 77, M.J.N.Sibley
Macmillan
New Electronics 1990
