Transient Response of MOS Capacitors to High-Energy Electron Irradiation

The response of Al-SiO2-Si (n-type) MOS capacitors to pulsed 30-MeV electron irradiation has been investigated for both positive and negative bias on the field plate. For samples under positive bias, the charge-transfer signal consists of two components. The first is due to carrier pairs generated in the oxide, which are swept at sufficiently high applied oxide fields to the electrodes before they can be trapped or can recombine, and consequently saturates at high fields. This component has been previously observed for low-energy irradiation which essentially did not penetrate completely through the oxide. The second component is approximately linear in applied field and is interpreted as being due to electron injection from the silicon substrate. Under negative bias, for which the interface of the silicon substrate is inverted, an entirely different transient behavior is seen. A large charge-transfer signal is observed during a 1-¿sec irradiating pulse. The magnitude of the total charge transferred is independent of bias voltage for sufficiently large biases and has only a very weak dependence on dose. The source of this signal, which for 100-rad(Si) pulses is over an order of magnitude greater than that observed under positive bias conditions, has been shown to be due to motion of hole-electron pairs generated in the depletion region of the silicon.