Ion-irradiation-induced effects on the surface characteristics of Ge–Bi–Se thin films

Abstract

In this study, fabricated amorphous chalcogenide Ge10Se70Bi20 thin films were irradiated with nitrogen (N+), argon (Ar+), hydrogen (H+) and oxygen (O+) ion beams. The compositions of the pure and irradiated films were investigated using X-ray diffraction, which confirmed the amorphous structures of the pristine and the irradiated Ge10Se70Bi20 thin films. The optical parameters such as optical bandgap, absorption edge, Urbach energy, Tauc parameter and extinction coefficient of the unirradiated and irradiated films were determined using ultraviolet/visible spectroscopy. The energy gap was found to reduce from 1.355 eV for unirradiated Ge10Se70Bi20 to 1.02, 0.73, 0.60 and 0.51 eV after irradiation with nitrogen, argon, hydrogen and oxygen ion beams, respectively. Meanwhile, the band tail of Ge10Se70Bi20, which is 0.12 eV, increased to 0.16, 0.40, 0.45 and 0.48 eV after irradiation with nitrogen, argon, hydrogen and oxygen ion beams, respectively. In particular, the conductivity increased by two orders after the pristine film had been exposed to an oxygen beam. The direct current electrical conductivity of the pristine film increased from 1.5 × 10−7 to 1.4 × 10−5 Ω−1 cm−1 after irradiation with an oxygen ion beam. Furthermore, the activation energy and Mott’s parameters of the original and irradiated Ge10Se70Bi20 films were deduced. The reported modifications of the optical and electrical parameters suggest the use of irradiated Ge10Se70Bi20 thin films in important applications – for example, optical data storage and optoelectronic devices.