The influence of photodiode design on receiver sensitivity

High bit rate communications systems require detectors with fast response, low noise and high responsivity in the wavelength range 1.3-1.55 μm. Historically this need has been met by using InP/InGaAs PIN photodiodes but increasingly InP/InGaAs avalanche photodiodes (APDs) have been used. However conventional III-V APDs (CAPDs) are inherently noisy and this has led to a search for material systems or device designs that will allow an APD to exhibit dramatically less noise while still absorbing in the 1.3-1.55 μm region. The author briefly describes theoretical work carried out to systematically compare the performance of several PIN and APD receivers and predict the probable performance of future APD receivers. For a comprehensive analysis two extremes of receiver amplifier quality are used-a low noise, high cost, transimpedance FET front end; and a higher noise, low cost, high impedance amplifier using a Si BJT. The work also uses three detector types-an `idealised´ InGaAs PIN photodiode with no significant dark-current; a conventional InP/InGaAs SAGM APD; and an advanced multilayer APD