Surface Effects of Radiation on Transistors

Observation of surface effects of ionizing radiation on several types of transistors indicates that in reverse-biased devices these effects occur at much lower radiation dosage than in unbiased devices or bulk semiconductor material. Further, the total radiation dose rather than dose rate seems often to be the more important factor in the effect. The type of particle used in irradiation is unimportant; the significant factor is the ionization it produces. The effects seem to arise from ionization of gases within a transistor encapsulation and interaction between the ionized gas and residual semiconductor surface contaminants. This results in inversion layers at the device surface and thus in alteration of junction characteristics. The changes in device properties are not permanent, but the recovery after removal from radiation is complex and proceeds with characteristic times between seconds and days. Different types of devices may respond quite differently to exposure, and the response is different even between different batches and individuals, indicating a dependence upon device processing. I. INTRODUCTION1 A wide variety of effects of high-energy radiation on semiconductor materials and devices has been recognized and studied for a number of years. The major emphasis in this field has been on effects that involve the bulk properties of semiconductors. A great deal of progress has been made in understanding the processes that control bulk radiation phenomena 1 and in understanding the implications of these phenomena for semiconductor devices.