The detector window thicknesses for carrier gas diffusions have been found to be very close to 1/2 the diffusion depths. This result is interpreted in terms of the concentration profile of the diffusant. In the surface region, where the impurity concentration is greater than 1018 per c.c., the carrier lifetime becomes so small that ionized charges recombine before they can diffuse to the junction. With reduced surface concentrations, window thicknesses of less than 1/2 the diffusion depth have been fabricated, but good voltage rating diodes with a window thickness of less than 0.1 micron (.025 mg/cm2) are yet to be realized. For all diffusion depths a non-noise resolution limit of devices has been observed which corresponds to approximately 1/3 the energy loss of an incident particle in the window layer of diodes. For paint-on diffusion detectors, the nominal 900Â°C - 10 minutes - 0.1 microns diffusion units have measured window thicknesses of about 0.3 microns. For the process studied it appears that an excessive amount of phosphorus is incorporated into the surface layer.