p-i-n Photodiode with a p+ Guard Ring

This paper presents the development and analysis of a silicon single-element p-i-n photodiode with a p+-type guard ring that is isotopically identical to the substrate. The proposed structural solution facilitates the fabrication process, ensures better parameter stability, and reduces the effect of surface inversion channels on dark current and device sensitivity. The base material was high-resistivity (18–22kΩ·cm), dislocation-free, monocrystalline p-type silicon with a 111 orientation. The device manufacturing process followed diffusion–planar technology, including consecutive formation of the p+ guard ring and the n+ light-sensitive region. Preliminary modeling of diffusion processes confirmed the absence of cross-doping between regions, revealed the dependence of dopant concentration profiles on depth, and also estimated the redistribution of dopant at the interface between materials during thermal-oxidative annealing and its subsequent changes during the diffusion stage. Measurements included both dark-current and photocurrent I-V characteristics, obtained at various wavelengths, in addition to the spectral response. The investigated photodiode demonstrated peak sensitivity around 950–970nm with a quantum efficiency approaching 0.9, while at the YAG laser wavelength the QE was reduced to about 0.4. Full depletion of the space-charge region across the substrate thickness was observed at Ubias−100V. At this voltage, the signal rise and fall times saturate at their minimum values (rise35–45ns, fall40–45ns), with no additional reduction at higher biases. The results obtained emphasize the strong potential of the developed photodiode for practical implementation in optoelectronic devices. Its combination of high quantum efficiency, fast response time, and operational stability makes it suitable for laser detection, precision measurement, and telecommunication systems.