Dependence of zero-bias resistance-area product and quantum efficiency on perimeter-to-area ratio in a variable-area diode array

The dependence of the zero-bias resistance-area (RA) product and the quantu m efficiency (eta) of variable-area diode arrays is numerically calculated by solving the diffusion equation in a cylindrical, three-dimensional geome try in the thick base approximation. The calculation is done for long-wavel ength IR HgCdTe n(+)-on-p diffusion-limited photodiodes at 77 K. The invers e resistance-area product 1/(RA) and the square root of the quantum efficie ncy, eta (1/2), are plotted against the perimeter-to-area (P/A) ratio. The 1/RA results are fitted to a quadratic dependence on the P/A ratio. The dep endence of the 1/RA on the minority carrier diffusion length, the junction depth and the surface recombination velocity (SRV) is evaluated. An empiric al expression is proposed that largely accounts for the dependence of the c oefficients of the quadratic on these parameters and is more general than t hose used in previous studies. The results are also in reasonable agreement with the results of Briggs, expressed in terms of the parameter f(3D), tha t are valid for zero junction depth and zero SRV. The slope of the quantum efficiency versus P/A plot, which is approximately a straight line, is rela ted to an effective length L-opt, that also depends on the diffusion length , junction depth, SRV and the absorption coefficient alpha. The parameter L -opt varies as alpha (1/2).