Design and fabrication of HgCdTe linear avalanche devices with low gain normalized dark current density

Abstract

Mid-Wavelength Infrared (MWIR) HgCdTe electron-initiated avalanche photodiodes (e-APDs) have presented excellent performances to resolve and count photons. Aiming at low flux, the Readout Integrated Circuit (ROIC) noise can be extremely reduced by certain device gain, and very low excess noise of HgCdTe e-APDs makes opportunity for noise equivalent photon (NEPh) to be one. Therefore, the main issue for Signal-to-Noise Ratio (SNR) 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, new combining dry/wet etching technology and passivation technology based on Plasma Atomic Enhanced Layer Deposition (PEALD) were used to reduce surface leakage current. Finally, 20 μm pitch 128×128 array HgCdTe APDs for cut-off wavelengths 4.32 μm @80K corresponding to compositions xcd 0.326 were fabricated, the measured GNDCD of test unit is about 1.5~50×10-9 A/cm2 at 0~13V