Dual Mode operation of High Gain Low Noise InGaAs APD

Indium Gallium Arsenide (InGaAs) photodetectors lattice-matched to InP substrates are widely employed for near-infrared detection due to their high quantum efficiency, low noise, and manufacturability. Conventional p-i-n (PIN) photodiodes provide excellent linearity and low dark current but lack internal gain, whereas avalanche photodiodes (APDs) offer enhanced sensitivity through impact ionization at the cost of excess noise, higher bias voltages, and temperature-dependent breakdown behavior. 

This work presents the design principles, device physics, and experimental performance of a dual-mode InGaAs photodetector derived from a PIN architecture that operates at unity gain at zero bias and transitions into controlled avalanche multiplication under reverse bias. By engineering the electric-field distribution such that the absorption region remains in a low-field regime, while avalanche multiplication is confined to a designated region, the detector enables low-noise radiometric measurements at gain = 1 and high signal-to-noise ratio operation at gains exceeding 10 using the same device and receiver electronics. 

Electrical, optical, noise, capacitance, and temperature-dependent characteristics are analyzed in the context of established InGaAs PIN and APD theory. The dual-mode approach offers system-level advantages for LiDAR, time-of-flight ranging, spectroscopy, and optical communication receivers requiring a wide dynamic range.