A theoretical assessment of low and high bandwidth gallium arsenide, germanium and silicon avalanche photodiodes for optical communication systems

A comparison is made of the relative properties of avalanche photodetectors for use in optical communication systems operating up to 1 GHz bandwidth over the wavelength range 730-1130 nm. Detectors for optical communications systems may have to operate at voltages limited by the electrical feeds to repeaters, hence the present comparison is for the specific case of diodes with a maximum operating voltage. The voltage used is generally 100V, but the analysis is also extended to 200V. The speed of the diodes is considered briefly then the main analysis compares the signal to noise performance of gallium arsenide, germanium and silicon diodes. The most recent noise theory is used incorporating the frequency dependence of multiplication and a detailed comparison is made of the results and their differences for the three materials analysed. In addition comparison is made with results using less accurate theories. The optimum diode material, for the simple uniformly doped 100V diodes considered, varies with wavelength and frequency. However the results show that there is no clear-cut choice and that, for instance, at long wavelengths (i.e. greater than 1·05 nm) germanium diodes, despite their high dark current, have comparable or better performance than silicon diodes for operation at 100V. Similarly in the conditions considered gallium arsenide photodiodes might provide an alternative detector for high frequency systems using gallium aluminium arsenide lasers.