The performance of an IR detector in an area array is studied by numerically solving the 2-D diffusion equation for thermal and photogenerated carriers. The zero-bias resistance area product R0A, quantum efficiency ?, and the noise equivalent temperature difference NETD for diodes of different size and junction depth are calculated for long wavelength infrared (LWIR) HgCdTe n+-on-p diffusion-limited diodes in the backside illuminated configuration. The 2-D calculations incorporate thermally generated- and photocarriers that originate under the junction (the ‘‘normal’’ current), as well as those that originate from around the junction (the lateral current). The calculation of the diffusion currents— both optical and thermally generated carriers—is made using a trapezoidal grid, which better fits the symmetry of diodes in an area array. The present results are compared with previous calculations in which a uniform grid was used. The results of R0A and ? calculated by the uniform and trapezoidal grids differ significantly, especially for diodes with deep junctions or diodes that are small compared to the center-to-center distance between diodes. Both the uniform and trapezoidal grid calculations have been compared with spot scan measurements and Semicad simulation in a stripe diode array in the literature.