HgCdTe APD- focal plane array development at CEA Leti-Minatec

Abstract

We report the latest developments of MW HgCdTe electron initiated avalanche photo-diodes (e-APDs) focal plane arrays (FPAs) at CEA-LETI. The MW e-APD FPAs are developed in view of ultra-sensitive high dynamic range passive starring arrays, active 2D/3D and dual-mode passive-active imaging, which is why both the passive imaging performance and the gain characteristics of the APDs are of interest. A passive mode responsivity operability of 99.9% was measured in LPE and MBE e-APDs FPAs associated with an average <i>NETD</i>=12mK, demonstrating that dual mode passive-active imaging can be achieved with LETI e-APDs without degradation in the passive imaging performance. The gain and sensitivity performances were measured in test arrays and using a low voltage technology (3.3V) CTIA test pixel designed for 3D active imaging. The CTIA and test arrays measurements yielded comparable results in terms of bias gain dependence (<i>M</i>=100 at <i>V_b</i>=-7V), low excess noise factor (<i><F></i>=1.2) and low equivalent input current (<i>I</i>_{eq_in}<1pA). These results validated the low voltage CTIA approach for integrating the current from a HgCdTe e-APD under high bias. The test array measurements demonstrated a relative dispersion below 2% in both MBE and LPE e- APDs for gains higher than <i>M</i>>100, associated with an operability of 99%. The operability at <i>I</i>_{eq_in}<1pA at <i>M</i>=30 was 95%. A record low value of Ieq_in=1fA was estimated in the MBE e-APDs at <i>M</i>=100, indicating the potential for using the MW e-APDs for very low flux applications. The high potential of the MW e-APDS for active imaging was demonstrated by impulse response measurements which yielded a typical rise time lower than 100ps and diffusion limited fall time of 900ps to 5ns, depending on the pixel pitch. This potential was confirmed by the demonstration of a 2ns time of flight (TOF) resolution in the CTIA e-APD 3D pixel. The combined photon and dark current induced equivalent back ground noise at <i>f/</i>8 with a cold band pass filter at &lambda;=1.55&mu;m was 2 electrons rms for an integration time of 50ns.