This paper analyses the spatial homogeneity of a large-diameter (100 mm) photodetector surface realized by recording the spatial distribution of the gas discharge light emission (DLE) in an ionization-type infrared image converter (ITIIC) with a GaAs photodetector. Analysis of the surface homogeneity is determined by the fractal dimension of the gas DLE when a current is passed through a converter cell. A fractal dimension estimation is found to be a powerful method because it enables both a non-destructive testing facility and use of the whole surface area of the photodetector surface in three dimensions. The effect on the roughness of the photodetector surface through plasmachemical processes at different experimental conditions was established. The effectiveness of the desorption process is proportional to the densities of bombarding particles as well as the stream of desorpted particles leaving the cathode surface. The surface images of the etched photodetector are analysed using both the profile and spatial distribution DLE intensity data showing the surface inhomogencity in the photodetector plate. It is quantitatively concluded that plasma etching at certain experimental conditions can cause an improvement in surface homogeneity of the photodetector and spatial distribution DLE in an ITIIC.