A low-voltage high-speed silicon photodiode with buried isolation region for short-haul optical-fiber communications

A new epitaxial silicon p-i-n photodiode has been developed for short-haul optical-fiber communications that can be operated at biases as low as 4 V. The device has a heavily doped 5-µm-thick p⁺⁺isolation-region between the p⁺substrate and the π-epitaxial layer. Fast rise and fall times (2 ns), and low leakage current (40 pA) result from the recombination and trapping of the minority-carrier electrons in the substrate. Experimental results on such an n⁺-π-p⁺⁺-p⁺device with 1.1-mm²photosensitive area and 25-µm epi-layer thickness show quantum efficiency of 80 percent at 825-nm wavelength.