Extremely low-noise avalanche photodiodes based on AlAs0.56Sb0.44

This paper presents the electron and hole avalanche multiplication and excess noise characteristics based on bulk AlAs0.56Sb0.44 p-i-n and n-i-p homojunction diodes lattice matched to InP, with nominal avalanche region thicknesses of 0.6 -1.5 mu m. From these, the bulk electron and hole impact ionization coefficients (alpha and beta respectively), have been determined over an electric field range of 220-1250 kV/cm for alpha and from 360- 1250 kV/cm for beta for the first time. Excess noise characteristics suggest an beta/alpha ratio as low as 0.005 for an avalanche region of 1.5 mu m in this material, close to the theoretical minimum and significantly lower than AlInAs, InP, or even silicon. This material can be easily integrated with InGaAs for networking and sensing applications, with modeling suggesting that a sensitivity of -32.1 dBm at a bit-error rate (BER) of 1x10(-12) at 10 Gb/s at 1550 nm can be realized. This sensitivity can be improved even further by optimizing the dark currents and by using a lower noise transimpedance amplifier.