High-Performance Long-Wavelength Infrared Avalanche Photodiode with Composition Gradient Layers

Long-wavelength infrared (LWIR) avalanche photodiodes (APDs) serve as the better choice for long-range detection and low-temperature object imaging due to the multiplication gain further enhancing the response sensitivity. However, the tunneling issue occurs in narrow-bandgap devices, and the surface leakage current significantly impacts the device available performance. In this work, we propose a novelty multilayer composition gradient LWIR APD device with a cutoff wavelength of 8 μm to address this series of problems. This design demonstrates high avalanche performance and effectively reduces surface leakage current and suppresses the tunnelling current. At 80 K, the unity-gain dark current of the device is of 7.16 × 10–7 A/cm2 and external quantum efficiency attains a peak of 78% (3.93 A/W) at 6.31 μm. This APD also displays a gain of 280 and low excess noise factor of 1.1. At a gain of 280, the device has a gain-normalized dark current density of 0.09 A/cm2. Furthermore, when the temperature increases to 160 K, the dark current remains relatively lower at 8 × 10–2 A/cm2, with a gain of 37 and an excess noise factor of less than 1.28. Thus, the composition gradient layers enable state-of-the-art performance in dark current, gain, and excess noise among LWIR APDs. This makes it highly promising for weak signal detection, imaging, and free-space optical communication applications.