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Abstract-A systematic study of impact ionization, avalanche multiplication, and excess noise in InAs diodes has been carried out, confirming that avalanche multiplication is dominated by the impact ionization of electrons. This results in highly desirable "electron avalanche photodiode" characteristics previously only demonstrated in HgCdTe diodes, which are discussed in detail. The suppression of excess noise by nonlocal effects, to levels below the local model minimum of F = 2, is explained. An electron ionization coefficient is calculated and shown to be capable of modeling the electron impact ionization, which differs characteristically from that in wider bandgap III-V materials.Index Terms-Avalanche photodiode (APD), electron avalanche photodiode (e-APD), impact ionization, InAs, ionization coefficient.

We report a versatile system for measuring excess noise and multiplication in avalanche photodiodes, using a transimpedance amplifier front-end and based on phase-sensitive detection, which permits accurate measurement in the presence of a high dark current. The system, which we have used successfully on a wide variety of materials and device structures, can measure reliably the excess noise factor of devices with a capacitance of up to ∼50 pF.

An experimental investigation into impact ionization in InAs photodiodes is presented. Photomultiplication measurements on p-i-n and n-i-p diodes show that while high avalanche gains can be obtained for electron initiated multiplication, there is virtually no gain with hole initiated multiplication. This indicates that the electron ionization coefficient is significantly greater than the hole ionization coefficient raising the possibility of extremely low noise InAs avalanche photodiodes when gain is initiated by electrons. The onset of electron initiated impact ionization was detectable at electric fields below 10kVcm−1 with useful gain observed at biases below 10V.

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