IRRADIATION EFFECTS OF HIGH-ENERGY HEAVY-IONS ON THE SWITCHING CHARACTERISTICS OF P-N-JUNCTION DIODES

The switching time of silicon diodes has been reduced from 1000 ns to less than 200 ns by introducing ion induced defects into the n-region of silicon junction diodes. These diodes were made on 250 mu m thick s ilicon wafers without adopting a gold diffusion process. The junction was located at a distance of around 60 mu m from the surface of the p- region. In these diodes since the thickness of the p-side is relativel y small as compared to that of the n-region, the switching characteris tics of the diodes are controlled mainly by the charge carriers of the n-region. In the present work, the lifetime of minority carriers in t he n-region has been reduced by creating defects through heavy ion irr adiation. The diodes were irradiated from the n-side with 100 MeV sili con ions, 70 and 80 MeV oxygen ions and 65 MeV boron ions covering a f luence range from 10(10) to 10(14) ions/cm(2). In this way, defects co uld be induced at different locations in the n-side covering a range f rom 35 to 140 mu away from the surface of the n-side. It has been obse rved that the defects produced near the junction are more effective in reducing the turn-off time t(rr) as compared to those produced near t he surface. On comparing the values of t(rr) for different diodes, it has been found that the defects induced by 65 MeV boron ions are most effective because even for a large decrement in the t(rr) the correspo nding increment in the forward voltage drop, V-f, was marginal. For ot her ions, though the decrease in t(rr) was effective, it was followed by a large increment in the V-f. In all the ion irradiated diodes, the increase in the forward voltage drop could be recovered partially aft er annealing the diodes at 450 degrees C, which however was followed b y a small increment in t(rr). Furthermore, almost all the ion induced defects could be annealed out at 600 degrees C. Results of this study indicate that heavy ions can be used effectively to control switching parameters of diodes with a much better trade-off between V-f and t(rr ) as compared to those exposed to Co-60 gamma rays or made with gold d iffusion.