University of Essex Nanofab

These pages provide an overview of the semiconductor device research and teaching nanofabrication facilities

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

 These pages are written & maintained by Adrian Boland-Thoms