Gain–Bandwidth Product Optimization of Short-Wavelength Infrared HgCdTe e-Avalanche Photodiodes

The short-wave infrared (SWIR) HgCdTe avalanche photodiodes (APDs) have demonstrated promising applications in low-flux and high-speed optical communication systems at high temperatures. However, the big gap between the theoretical highest gain-bandwidth product (GBP) and the reported performances indicates that there is still room for device optimization. In this work, numerical models were established for the 3-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m cutoff wavelength SWIR HgCdTe electron-initiated APDs (e-APDs) working at 140 K. The absorption and multiplication layer thickness dependence of the impulse response and multiplication gain has been characterized. Our results show that a thinner absorption and multiplication layer will enhance the bandwidth performance, and a mesa structure device can achieve a higher bandwidth compared to a planar one. The tradeoff between the bandwidth and multiplication gain was analyzed to optimize the GBP of the device. The structural optimization increases the device bandwidth from 300 to 750 MHz and achieved a 21-GHz GBP at 16 V bias. Specially, the high GBP and ability to maintain a low excess noise factor make HgCdTe APDs extremely valuable for high-quality signal transmission applications.