JFET/SOS (Junction Field-Effect Transistor/Silicon-on-Sapphire) Devices: Gamma-Radiation-Induced Effects.

Abstract : Enhancement and depletion mode JFETs have been fabricated on silicon-on-sapphire substrates. When these devices are irradiated under bias with a 60Co source, their drain currents increase, and their threshold voltages shift in such a way that the devices become more difficult to pinch off. These effects can be explained by positive charge trapping at the silicon/sapphire interface. Gate to drain leakage currents also increase, and can be traced to interface effects at the gate edges rather than to the passivating oxide. These effects were studied as a function of dose rate and postirradiation annealing. Deep-level transient spectroscopy (DLTS) was performed prior to and following both irradiation and anneal on both the gate-drain and gate-source p-n junctions. DLTS trap bands were observed whose characteristics depended on the depth of the depletion layer and on the total gamma dose received. The DLTS spectra suggest that a continuum of levels is responsible for the bands, and that the emission kinetics are influenced by band bending at the Si/sapphire interface. The major bands corresponded in temperature with steps in capacitance-temperature curves. A correlation of these steps with the transistor characteristics suggests that channel pinch off can be influenced by capture and emission at deep centers. Keywords: Cobalt 60; Deep level transient spectroscopy; Junction field effect transistor; Radiation effects; Silicon on insulator; Silicon on sapphire; Transistor; Semiconductors devices.