| dc.description.abstract | So far, avalanche photodiodes(APD) operating at near Geiger-mode have played a vital role for detecting extremely weak light (single or a small number of photons) in variety of applications. For example, single-photon detectors(SPAD), time-of-flight(ToF) or frequency modulated continuous wave(FMCW) Lidar systems and optical time domain reflectormeters(OTDR). To satisfy the requirements of such applications, we need APDs with large window size, moderate bandwidth, high responsivity. However, it’s difficult to design APDs capable of meeting the afore-mentioned performance requirements due to the limitation of gain-bandwidth product(GBP). In this paper, we conquer the GBP bottleneck by using thick absorption layer(2μm) and triple In0.52Al0.48As based multiplication layer. Moreover, the characteristic invariant 3-dB bandwidth in our APDs, from low to an extremely high operation gain, becomes more pronounced with an increase of its active window diameter (40 to 200 μm). This characteristic makes it very attractive for the receiver detecting the extremely weak light in FMCW Lidar applications. Comparison shows that the 200 μm APD exhibits a higher 0.9 Vbr responsivity (15 vs. 7 A/W), larger maximum gain (460 vs. 110), and higher GBP (468 vs. 131 GHz) than does the 40 μm reference sample and can sustain a constant 3-dB bandwidth (1.4 GHz) over a wide range of operation gains (10 to 460). The dependence of the APD performance on the window size can be attributed to the influence of the surface states on the edge of the etched mesa. In this paper, we further demonstrate a backside-illuminated structure with a flip-chip bonding package which minimizes this phenomenon in small APDs ensuring high-speed performance. Compared with the top-illuminated reference samples, the flip-chip bonding packaged device shows a further enhancement of the responsivity (10.7 vs. 7 A/W), 3-dB bandwidth (4.1 vs. 3.9 GHz), and saturation current (4.25 vs. 3.6 mA). The excellent static and dynamic performance of our flip-chip APD in turn leads to an unprecedented high velocity sensitivity (5 μm/sec) and superior quality 4-D FMCW LiDAR images compared to that obtainable with p-i-n-based or top-illuminated reference devices with the same small active window size (40 μm). | en_US |