Design of Neutron Radiation Tolerant High Effitciency Microwave Avalanche Diode Sources (Trapatt Oscillators)

The effects of permanent neutron damage on the operation of high efficiency avalanche microwave sources are explained. The resulting design criteria for increasing the neutron radiation tolerance of these devices are verified by comparing experimental results for two different device doping profiles. In terms of RF failure, the device with the narrower space-charge region is more radiation resistant. This is because RF failure is related to recombination of carriers as they transit the space-charge region. A theoretical curve predicting neutron damage failure versus frequency of operation is presented and shown to agree with the experimental data taken from the two different TRAPATT oscillators. The DC failure of the devices takes the form of a negative temperature coefficient at large reverse breakdown currents which is related to carrier removal at the edges of the space-charge region. In terms of this DC failure mechanism the device with the more abrupt doping profile is more radiation tolerant.