The effect of gamma-ray (γ-ray) irradiation on the material characteristics of nanometre scale films of molybdenum disulphide (MoS 2) has been investigated. 3.2, 4.5, and 5.2 nm thick MoS 2 films (measured by atomic force microscopy) were grown on Si by using a two-step synthesis method (sputtering of Mo, followed by sulphurisation). The samples were subsequently exposed to γ-ray irradiation (dose of 120 MRad). Dramatic chemical changes in the MoS 2 films after irradiation were characterised by micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and optical microscopy. Micro-Raman spectroscopy showed the disappearance of the E 2g 1 and A 1g modes after irradiation. XPS revealed that the MoS 2 crystal structure was converted to molybdenum oxide (MoO x). It is hypothesised that S vacancies are formed due to the γ-ray irradiation, which subsequently transforms MoS 2 to MoO x .

A comparative study on the direct-current (dc) electrical performance and optical characteristics of unirradiated and 120 MRad 60Co-gamma-ray (γ-ray) irradiated AlGaN/GaN high electron mobility transistors (HEMTs) was performed. The devices fabricated on an irradiated HEMT epilayer structure show slight degradation/alteration in the dc characteristics such as source–drain current–voltage (IDS-VDS), transfer (IDS-VGS), transconductance, and gate current–voltage, indicating the presence of radiation-induced defects. Also, a shift in flat band voltage was observed from the capacitance-voltage measurements. Micro-Raman spectroscopy and photoluminescence (PL) spectroscopy were used to compare the crystal quality of the heterojunction. No shift in the Raman peak frequency position was observed in both the unirradiated and irradiated samples, which implies that the irradiation did not produce an additional strain to the HEMT layers. However, the full width at half maximum of the Raman and near-band-edge PL peaks has increased after irradiation, which suggests the degradation of crystal quality. The spectroscopic photocurrent–voltage study with sub-bandgap and above bandgap illumination confirmed the pre-existence of sub-bandgap defects in the heterostructure and revealed the possibility of their rearrangement or the introduction of new defects after the irradiation. It was concluded that AlGaN/GaN HEMTs are relatively resistant to high dose (120 MRad) gamma-ray irradiation, but they can introduce additional traps or reconfigure the pre-existing traps, influencing the electrical and optical characteristics of AlGaN/GaN HEMTs.