The trapping of N2 molecules and the reduction in its bonding length in Ge(001) due to N2+ ion implantation

Abstract

To find the cause of N2 → N + N dissociation in Ge(001) at low temperature, the N2+ ion implantation process was carried out on a Ge(001) substrate, followed by rapid thermal annealing (RTA). After N2+ ion implantation, the presence of N2 molecules and the chemical states of GeNx were determined using near-edge x-ray absorption of fine structure (NEXAFS) and high-resolution x-ray photoelectron spectroscopy with synchrotron radiation, respectively. Rapid thermal annealing was performed at 600 °C, after which a change in chemical state from the chemically meta-stable state of GeNx to the stable state of Ge3N4 was observed. In addition, the intensity of the N2 vibration mode peak in NEXAFS was decreased, although it did not completely disappear. To explain the N2 →N + N dissociation at the low temperature, a first-principle calculation for N2 bonding length was performed in both vacuum and Ge(001) states. We confirmed that implantation resulted in the trapping of N2 molecules in Ge(001), and their bonding length was changed from 1.117 to 1.205 Å at a difference energy of 2.529 eV. It was assumed that the relaxed change in the N2 bonding length originated from the dissociation of N2 molecules at low temperature.