Three-dimensional numerical analysis of diffusion current and quantum efficiency of small area Hg1-xCdxTe photodiodes

Numerical techniques were used to solve the 3-dimensional diffusion equation for planar circular n⁺on p Hg1-xCdxTe photodiodes of radius "a". This is the first time that both the lateral contributions to the p-side diffusion current (limiting zero bias impedance Ro) and the photoresponse have been calculated for small area photodiodes. Our analysis reveals the saturation current ISATis conspicuously independent of both lifetime τeand diffusion length Lefor diode dimensions small compared with diffusion length, whereas for larger diode dimensions we find . Hence no additional reduction in ISATnor increase in Rooccurs for improvement in Lebeyond about 4a for all p-side thicknesses. The lateral contributions to photocurrent for front side diode illumination were used to determine the performance tradeoffs from choice of photodiode junction area for fixed optical area.