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This paper constitutes the analysis of the impact of low doped intrinsic p-type EPI thickness (20 µm and 30 µm) and bottom anti-reflective coating on the electrical and optical performance of various PIN photodiodes designs. The intrinsic p-type layer with a target resistivity of 400 Ω cm is an epitaxial layer (iEPI) grown on a low resistive substrate of 20 mΩ cm. Optimization of the photodiode’s spectral responsivity (for a specific wavelength) includes a Bottom Anti-Reflective Coating (BARC) layer deposited over the silicon surface. BARC thickness is optimized for λ = 425 nm, λ = 750 nm and λ = 900 nm wavelengths. With respective BARC in place, the photodiode’s quantum efficiency (QE) approaches 100% for λ = 750 nm with 20 µm and 30 µm iEPI thickness and for λ = 900 nm with 30 µm iEPI reaching also a maximum spectral response of 0.63 A/W at 800 nm. QE of 72% could be achieved at 425 nm. The leakage current varies from 3.5 pA for 20 µm iEPI thickness to 10 pA for 30 µm at 1 V reverse biasing for 365 µm circular PIN photodiode.

Many imaging applications, like medical or space applications, require radiation-hard sensors. Generally, during radiation, many different defects are created, depending on the type of the radiation. With TCAD software, cross-section of a radiation-hard photodiode was simulated, and afterwards the impact of different physical parameters was simulated. Physical parameters like epitaxial layer thickness or the trap density in the bulk, play a huge role towards the responsivity of the photodiode. This paper presents a variation experiment, where relevant physical parameters are varied and analysis of the spectral responsivity and dark current of the photodiode is discussed.