Avalanche Photodiodes With Dual Multiplication Layers and Ultra-High Responsivity-Bandwidth Products for FMCW Lidar System Applications

In this work, we demonstrate a novel In _0.52 Al _0.48 As based top-illuminated avalanche photodiode (APD), designed to circumvent the problem of serious bandwidth degradation under high gain (>100) and high power operation and significantly enhance the dynamic range in the established frequency modulated continuous wave (FMCW) lidar system. In our APD design, the carriers transiting through the dual multiplication (M-)layers are subjected to a stepped-up electric field profile, so they can be energized by the first step and propagate to the second step to trigger the avalanche processes. Such a cascade avalanche process leads to an ultra-high gain bandwidth product (460 GHz) with a 1 A/W responsivity at unit gain. Compared to the high-performance and commercial p-i-n PD and photo-receiver (PD + trans-impedance amplifier (TIA)) installed in the same lidar test bed, our demonstrated APD receiver (without TIA) has a larger S/N ratio under high operation gain (33 A/W) with less optical local-oscillator (LO) power required (0.25 vs. 0.5 mW), while exhibiting a wider dynamic range in each pixel. These advantages in turn lead to the construction of a better quality of 3-D lidar image by using the demonstrated APD.