Silicon Based Schottky Diodes and MOS Capacitors for Sensing Singly and Multiply Charged Ions with Low Kinetic Energy

This study provides the foundation for the development of radiation detection technology of slow ions by investigating the fundamental interactions of slow ion beams with electronic devices. Silicon samples with a 50 nm oxide layer were irradiated with 1 keV ArQ+ beams (Q = 4, 8, and 11) at normal incidence in order to investigate the relatively unexplored effects of slow highly charged ions (HCIs) on electronic devices. After irradiation, an array of metal contacts was deposited onto the oxidized silicon samples to create metal oxide semiconductor (MOS) capacitors, which were then characterized using high frequency capacitance-voltage (C V) measurements. The slow HCI irradiation was found to result in stretchout and shifting of the C-V curves, indicating the presence of dangling Si bond defects at the semiconductor/oxide interface and trapped oxide charge, respectively. Near quadratic charge state dependencies were also observed for both the stretchout and the shift seen in the C-V curves, in agreement with charge state dependent stopping power of HCIs previously reported. The interaction of slow singly charged ions with Schottky diodes was also investigated, in part to serve as a baseline for experiments with slow HCIs by isolating the effects of the kinetic energy of the ions. Diodes with two different Schottky contact thicknesses (~26 nm and ~360 nm) were irradiated by Na+ beams at normal incidence with energies 0.5 keV, 1.0 keV, 1.5 keV, and 2.0 keV. No instantaneous change in diode current was observed while the diodes were under irradiation; however, noticeable changes in Schottky barrier height, ideality factor, and reverse leakage current were noted after irradiation. The diodes irradiated at 2.0 keV showed signs of degradation consistent with reports from the literature, but at the three lower ion beam energies the diodes showed an improvement in the ideality factor accompanied by an increase in Schottky barrier height and an initial decrease in reverse leakage current. Although the direct mechanism for these diode improvements is not fully understood, it is proposed that the changes arise from increased spatial homogeneity of the Schottky barrier height across the diode