Study on dark current suppression of HgCdTe avalanche photodiodes for low flux photon detection

Mid-wavelength infrared HgCdTe electron-initiated avalanche photodiodes (e-APDs) have presented excellent performances on resolving and counting photons. Aiming at low flux, the readout integrated circuit noise can be significantly reduced by certain device gain, and very low excess noise of HgCdTe e-APDs gives the opportunity for noise equivalent photon (NEPh) to be 1. Therefore, the main issue for signal-to-noise ratio of HgCdTe APD is gain normalized dark current density (GNDCD) at high reverse bias. In this work, the electric field distribution is optimized by designing the mesa device structure to suppress the tunneling current at high operating voltage. Furthermore, etching technology combining dry etching and wet etching and passivation technology based on plasma enhanced atomic layer deposition were used to reduce surface leakage current. Finally, 20 μm pitch 128 × 128 array HgCdTe APDs for cutoff wavelength 4.32 μm at 80 K corresponding to compositions xCd = 0.326 were fabricated, the measured GNDCD of the test unit is about 1.5–10 × 10−9 A/cm2 at 0–13 V, and very low excess noise guaranteed the NEPh to be 2.0 at gain = 93 and 1.6 at gain = 193.