The GaN-based heterostructures and related HEMTs (High Electron Mobility Transistors) were investigated by 1MeV neutrons at fluences up to 10¹⁵ cm⁻², yielding an increase of the densities of screw dislocations and edge dislocations for GaN-based heterostructures. It gave the result that neutron irradiation-induced structural defects into GaN-based materials, and the irradiation-induced dislocations would propagate to the material surface causing surface morphology deterioration. However, the GaN-based material strain was robust to neutrons, and the more initial dislocations, the easier to generate irradiation defects and thus, more strongly affecting the electrical property degradations of materials and devices. Meanwhile, the reduction of the two-dimensional electron gas (2DEG) concentration (n_s) caused by irradiation-induced defects led to the reducing the drain current. Moreover, the significant degradation of the reverse gate leakage current at fluences ranging from 10¹⁴ to 10¹⁵ cm⁻² could be attributed to the irradiation-induced deep defects. The neutron induced damage was more difficult to anneal recovery than other particles, due to the neutron irradiation-induced deep levels and defect complexes such as defect clusters.

We developed an adsorption model to examine secondary electron (SE) emission from a surface adsorbed by N ₂ molecules. In this model, the scattering processes of electrons and N ₂ molecules are simulated by Monte Carlo method. The traces of both primary electrons (PEs) and SEs are tracked by combining the electron scattering in the material and adsorbed layer. The SE yield (SEY) is then calculated from the final states of electrons that can emit out from the adsorbed layers. Moreover, the effects of the work function variation induced by adsorption are also taken into account in the model. The SE emission properties of the surface under different pressures and surface coverage are examined by our adsorption model. We find that the SEY reaches its minimum for an intermediate coverage of 1 ~ 2 × 10 ¹⁵ /cm ² for the Cu substrate. Further investigations on returning and outgoing ratios and energy distributions of SEs indicate that an adsorbed layer can generate new electrons but weaken the electron energy, especially at a high PE energy. The competing mechanism of ‘SE generation event’ and ‘energy losing event’ controls the variation of SEY. Accordingly, our model could serve as a powerful tool and our results can provide comprehensive insight into the SE emission of the surface covered by gas molecules, thereby helping us to find a rationale for the behaviour of SEs under various surface conditions.

The secondary electron spectrum (SES) contains complex surface information and is widely used in surface analysis technology. A theoretical model of the SES for metals was proposed to reveal the effect of the surface potential barrier on the SES. In our model, an improved inner secondary electron energy distribution was established according to the free electron gas model. The transmission coefficient of inner secondary electrons was determined by solving the density of electronic states. Finally, the model was verified by our experiments, and the effects of the coverage fraction and potential barrier height, width, and form on the SES were comprehensively analyzed. The results show that H2O adsorption lowers the barrier height and enhances the tunneling effect, resulting in the most probable energy shifting toward the low-energy end and full width at half maximum narrowing. In addition, increasing or broadening the barrier can weaken the secondary electron tunneling effect, reduce the secondary electron number, and increase the most probable energy and the full width at half maximum. The model in this paper provides a reliable analysis method for studying the SES under different surface barriers for metals. Relevant results have significant value for the analysis of scanning electron microscopy images and optimization of secondary electron detection systems.

Secondary electron emission (SEE) critically limits the performance of high-power microwave components and particle accelerators. Amorphous carbon (a-C) films featuring a low secondary electron yield (SEY) and surface grooves offer promising applications for suppressing the SEE effects. However, the efficiency of SEE suppression and the underlying microscopic mechanisms remain subjects of debate. This paper employs the Monte Carlo method to develop a novel electron scattering and an SEE model for copper surfaces coated with a-C films and patterned with rectangular grooves. The model accurately simulates electron transport within the film and substrate, explicitly accounting for the influences of the film/substrate interface energy barrier and the groove walls on electron scattering trajectories. Results demonstrate that increasing the a-C film thickness from 0 to 5 nm reduces the maximum SEY from 1.18 to 0.82. The SEE suppression effect is significantly enhanced on grooved a-C surfaces. Specifically, with a groove depth of 30 nm and a film thickness of 5 nm, the maximum SEY reaches a minimum value of 0.47. These findings provide important insights into the mechanism by which grooves and a-C films suppress SEE and offer practical guidance for designing high-performance, low-SEY surfaces for the next generation of high-power devices.