High-speed PiN photodiode design space exploration to break the speed-efficiency trade-off

Ever-evolving imaging and low-to-single photon-count detection applications demand high-speed, efficient, and complementary metal oxide semiconductor (CMOS) compatible photodetectors. Due to the non-overlapping research and development in the CMOS logic and optoelectronic industry, holistic system optimization is lacking. We propose a PiN device design method addressing the speed-efficiency trade-off and enabling an independent optimization of both speed and absorption efficiency. We present a hybrid device structure combining lateral and vertical PiN architectures. We introduce a highly doped buried P+- region connecting the top P+- contact doping and separating the N+-contact doping by a critical width. The top P+- and N+- contacts are laterally separated by an i-layer for absorption. The use of a lateral i-layer enables a larger volume for efficient photon absorption, and the presence of a highly doped P+- region enables an efficient collection of slow-moving holes after the illumination is turned off. The critical i-layer width sandwiched between the buried P+- region and the N+- contact doping facilitates an efficient conduction path. We optimize the critical width (optimized width = 200 nm) for device capacitance and the admittance to maximize the response time (rise time, fall time, and full-width half maxima). The optimization is performed using ATLAS Silvaco technology computer-aided design software. The optimized device structure possesses 22 GHz 3 dB bandwidth (BW = 0.35/Fall-time) at 850 nm illumination wavelength as against 0.6-10 GHz 3 dB bandwidth range for conventional PiN devices. We also show that reducing the critical width to zero results in impact ionization drive avalanche phenomenon at similar to 6 V applied bias, making these devices suitable for low-power and low-photon count detection. With a large absorber width, an optimized critical conduction path, and a low-bias trigger avalanche process, the proposed photodiodes result in high-speed, high-bandwidth, low-photon count detection, essential for state-of-the-art light detection and ranging systems and the single-photon detectors for quantum communications.