Effects of irradiation-induced defects in germanium

Abstract

In this study, we investigated the electrical characteristics of defects in germanium produced by alpha particle radiation using conventional deep level transient spectroscopy (DLTS) and Laplace deep-level transient spectroscopy (L-DLTS). Resistive deposition was used to fabricate palladium (Pd) and silver-gold (Ag/Au) Schottky contacts. I-V and C-V measurements were used to determine the suitability of the device by calculating the ideality factor (n) and carrier concentration (Nd). The Pd/n-Ge Schottky diodes were of high quality with ideality factor n = 1.159 before irradiation. After irradiation, ideality factor increased to n = 1.383, showing that exposing the device to irradiation, Schottky diodes of the device degraded. The carrier concentration of the devices from the C-V graphs, where the plot representing the samples before irradiation, was observed to be steeper compared to the plot before irradiation, indicating a decrease in free carrier density from 1.52×1016 cm-3 for an unirradiated sample to a 6.37×1015 cm-3 irradiated sample. A DLTS spectrum of the unirradiated germanium did not show any electrically active defects in detectable concentrations. After irradiation, DLTS spectrum illustrated the presence of several defects: E07+04, E10, E16+17, E23+25, and E37 (E+Eʹ). Peaks E and E’ were separated at 185 K by L-DLTS using manual regularization parameters, allowing the inversion routine to take into consideration the possibility of two or more closely spaced peaks. Conventional DLTS spectrum were also recorded for different pulse widths, and the peak height was reduced with a shorter pulse width, indicating that partial trap recharge was hardly observed for defects with pulse widths of 100 ns and 1 µs. The peak height started intensifying from 10 µs to 1 ms, which is a longer pulse width until it reaches saturation, meaning that all traps were now filled. The activation energies for all observed defects were calculated from the Arrhenius plot. Defects E25, E23, E10, E0.07, and E0.04 were observed after irradiation, but they were not all fully characterized. AuAg/Ge samples measurements illustrated the presence of 6 peaks after irradiation, which revealed an additional peak with an activation energy of 0.21 eV, defect E21 when compared to Pd/Ge samples. The electrical properties of E and E’ defects in germanium (Ge) introduced by alpha particle radiation were studied using high-resolution Laplace deep-level transient spectroscopy (L-DLTS). From the Arrhenius plot, it was observed that the E-centre consists of two components with similar DLTS signatures, but they have different properties, given that they have different activation energies of Et 0.375 eV and 0.370 eV. Electric field dependence of the E defect was measured at different temperatures to distinguish between Poole-Frenkel and phonon-assisted tunnelling, it was observed that the emission of carriers was described by phonon-assisted tunnelling for all measurements at different temperatures. The defect's depth profile measurements for the E-centre showed that as we probe deeper into the bulk of the semiconductor, the concentration of the E-centre defect decreases. The DLTS amplitude of the combined E and E' defects increased as the filling pulse width increased from a few microseconds to a millisecond. However, the DLTS amplitude of E was observed to be 4 times bigger than the DLTS amplitude of E' and both defects are structurally different