High-Speed Planar InGaAs/InAlAs Avalanche Photodiode

This letter describes a planar avalanche photodiode (APD) with 3dB bandwidth of 40 GHz at gain of 2.5, which is the highest bandwidth among reported vertical planar InAlAs APD. The APD adopts selective Zn diffusion to form the planar structure. Scale of the APD can be easily reduced to meet the needs of high-speed operation. The added p/n double charge layers can accurately adjust the electric field distribution inside the APD. By optimizing the thickness of the absorption and the transit layers, a compromise can be determined between carrier transport time and capacitance to achieve high bandwidth. An equivalent circuit of planar APD was established, laying the foundation for characteristics performance optimization. The fabricated APD uses 90 nm InAlAs as the multiplication layer and the dark current is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~{\mu } $ </tex-math></inline-formula>A. The responsivity of the top-incidence APD without anti-reflection is 0.15 A/W at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.55~{\mu } $ </tex-math></inline-formula>m. The gain reaches 45 when the incident light intensity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~{\mu } $ </tex-math></inline-formula>W.