Surface effects of radiation on semiconductor devices

A brief review of surface physics is given as background for the subsequent discussion on the role of surfaces in the behavior of semiconductor devices. The effects of channels and surface generation-recombination on p-n junctions and transistor characteristics are discussed. The observed effects of ionizing radiation on nonpassivated, gas-filled transistors are interpreted in terms of a model in which ions formed in the gas ambient deposit charge on the device surface. The resultant surface charge buildup creates channels on the device surface which cause a decrease in hFE and increase in ICBO. Saturation, recovery, and the effects of dose rate and bias are also discussed. Degradation of planar passivated transistors and other devices employing SiO2 layers due to radiation is similar to that observed for nonpassivated devices. Surface charge buildup affects the device surface and leads to degradation. The bulk of experimental evidence points to accumulation of positive charge at the SiO2–Si interface as the cause of degradation. Several possible means of charge buildup at the interface are discussed. However, the process responsible has not, as yet, been identified. The direction of future experiments is discussed, particularly of those experiments which may yield information about the part played by radiation in positive charge accumulation at the SiO2–Si interface.