Ultra-Fast/THz, High-Power Photodiode

To date there are two major commercially available lidar systems. One is direct detection (DD) time-of-flight (ToF) lidar and the other is frequency-modulated continuous-wave (FMCW) lidar system. In these two technologies, two different receiver end schemes are adopted to handle the weak reflected light. The ToF system usually adopts single-photon APDs operated at Geiger mode with infinite gain for direct-detection (D-D). With respect to FMCW lidar, the high-linearity p-i-n photodiode (PD) integrated with the self-heterodyne beating detecting setup is usually preferred for serving as its receiver-end. In this work, we review our recent progress about a In0.52Al0.48A based vertically-illuminated APD with a novel design of dual multiplication (M-) layer, which can attain remarkable static and dynamic performances at both linear and Geiger mode operations. High output photocurrent (~12 mA) with high-responsivity (6.3 A/W) and high single-photon detection efficiency (61% @ 200K) with short jitter (65 ps) have been successfully demonstrated under 0.9 Vbr and Geiger-mode operation, respectively. These measurement results create new possibilities in the next generation lidar systems.

Fig. 1. Conceptual cross-sectional view of the demonstrated APDs with quadruple mesa structure. Inset shows the top-view photo of fabricated devices with 60 and 200 Micrometer active optical window diameter.

Fig. 2. The measured dark current, photocurrent, and operation gain versus bias voltages under different optical pumping powers for the demonstrated APD operating at a wavelength of 1.55 μm for (a) Device A and (b) Device B, respectively.

Fig. 3. The measured DC output photocurrent versus input optical input power for (a) device A and (b) device B at 1.55μm wavelength and under different reverse bias voltages.

Fig. 4. Conceptual diagram of our established FMCW lidar system with APD Rx (Device A). FG: function generator. EDFA: erbium-doped fiber amplifier. ESA: electrical spectrum analyzer. Solid line: optical path along the fiber. Dashed line: optical path in free space.

Fig. 5. (a) The captured lidar images based on the measured IF power of each pixel from device B. (b) The captured lidar 3D images based on the measured IF frequency and depth information of each pixel from the device B.

Fig. 6. DCR per area versus the SPDE for triple and quadruple mesa devices at different gate width operations and the temperature of 200 K and 300 K. The inset shows the Arrhenius plot of DCR for the gate width of 1.5 ns (solid symbol) and 5 ns (open symbol). The activation energy can be calculated from the slope of the Arrhenius plot.

Fig. 7. (a) Timing jitter versus excess bias for triple and quadruple mesa devices at different gate width operations and the temperature of 200 K and 300 K. (b) Gaussian-like temporal responses measured at Vex= 4.1 %, 5ns gate width and T= 200 K for quadruple and triple mesa device.