Evaluation of the transit time and frequency response of multifinger PIN SOI photodiodes at IR and UV wavelenghts

This paper addresses a simultaneous analysis of the intrinsic length (L_I) variation and substrate doping concentration on the AC operation of multifinger SOI PIN photodiodes, in order to investigate the best performance for each application. The results showed that the best frequency response was achieved for devices with smaller L₁ values and higher substrate doping concentrations, reaching a 3 dB frequency of 10 GHz with 400nm of wavelength. However this configuration causes an efficiency reduction, decreasing the photogenerated current and consequently the responsitivy of the device, due to the smaller photosensitive area. The performance of the diodes was analyzed in the UV and IR range. In the first case, SOI photodiodes demonstrated excellent responsivity and high speed operation because the influence of the capacitive effect of BOX can be neglected, since most of the light radiation is absorbed before reaching the substrate, which proves the excellent SOI device performance for applications that requires higher current levels (greater responsivity) in the UV range. However, in applications for short distance optical communication, which require the use of wavelengths in the IR range, the SOI device has demonstrated low responsivity, but also presents excellent speed of response.