Using the Monte Carlo method, the energy losses in silicon carbide of heavy ions with different linear energy transfers (LETs) are simulated and calculated. The simulation results show that the energy loss per unit depth of heavy ions in silicon carbide is affected by both the ion energy and the incident depth. Primary heavy ions and secondary electrons mainly cause energy loss, and the non-ionization energy loss only accounts for about 1% of the total energy loss. With the increase of LET, the initial angle and energy distribution of the secondary electrons become more and more concentrated. The peak position of the generated charge deposition is in the center of the heavy-ion track, and the distribution is linearly decreasing in Gaussian form in the direction perpendicular to the incident depth. In the californium source experiment of SiC MOSFET, when the drain voltage is 480 V, the device has a single event burnout, and the breakdown voltage of SiC MOSFET is less than 1 V after burnout has occurred. With the experimental results, we carry out the TCAD simulation of SiC MOSFET and obtain the electric field distribution inside the device under different drain voltages. The electric field parameters are used in the Monte Carlo simulation of SiC MOSFET with considering the metal layer. It is found in the Monte Carlo simulation that the greater the electric field of the epitaxial layer, the longer the path of heavy ions moving on the epitaxial layer is and the more the deposited energy, and that the secondary electrons are more likely to move in the direction of the electric field as the electric field increases, resulting in excessive energy deposition in local areas.

As a type of two-dimensional (2D) semiconductor material, 2D germanium selenide (GeSe) exhibits excellent optoelectronic properties, and has potential applications in optoelectronic devices. The GeSe is a layered material with weak van der Waals interaction. Because of the high brittleness of GeSe, it is not easy to obtain 2D GeSe samples only by mechanical peeling technique. In order to obtain a thinner GeSe sheet, we use heat treatment to thin the bulk GeSe at a high temperature in vacuum. The GeSe samples obtained by mechanical peeling are placed in a tubular furnace with a pressure of 5 × 10^-4 Pa for high temperature heating and thinning. In order to explore the better thinning effect, we set four temperatures to be at 320, 330, 340 and 350 ℃, respectively. After high temperature thinning, the samples are characterized and observed by atomic force microscope (AFM), scanning electron microscope (SEM), Raman spectrometer and photoluminescence (PL) spectrometer. From the above experiments, the GeSe nanosheet with a thickness of about 5 nm is prepared by mechanical peeling and high temperature thinning technology. Then, the electrical conductivities of GeSe nanosheets in oxygen (O₂) and butane (C₄H₁₀) with different concentrations are evaluated by our designed experimental device. The results show that with the increase of oxygen concentration, the electrical conductivity of GeSe nanosheets increases. When the GeSe nanosheet is in butane gas, its conductivity under the same voltage decreases with the increase of the concentration of butane gas. In order to further analyze the mechanism of gas adsorption on GeSe nanosheets, we carry out the first-principles calculations. Our calculation results show that the adsorption energy of GeSe nanosheets for oxygen and butane is –4.555 eV and –4.865 eV, respectively. It is shown that both adsorption systems have a certain stability. The adsorption energy of C₄H₁₀ is smaller than that of O₂, which corresponds to the smaller layer spacing of C₄H₁₀ than that of O₂ on GeSe surface. From Bader analysis, it is shown that 0.262<i>e</i> is transferred from the surface of GeSe nanosheet to O₂ molecule, which is much larger than 0.022<i>e</i> transferred from GeSe to C₄H₁₀ molecule. It can be inferred that the bond formed between GeSe and O₂ molecule is covalent bond, while GeSe adsorption C₄H₁₀ is very fragile hydrogen bond adsorption. In an ideal condition (single atomic GeSe layer, no Se vacancy, and the device preparation process is vacuum), our calculation results show that C₄H₁₀ still has a weak ability to obtain electrons from the GeSe nanosheet. However, the complex conditions such as the actual layer thickness, the appearance of Se vacancy and the adsorption of O₂ molecules on the surface leads to the difference between the experimental results and the theoretical calculations, which can be attributed to the adsorption of O₂ molecules on the GeSe surface from the air during the processing of GeSe thinning and device fabrication. Owing to the high density of Se vacancies in the thin film, the high density of O₂ adsorption is caused. Thus, butane gas is easy to lose electrons on the GeSe surface due to the O₂ adsorption. In other words, electrons are transferred from butane gas molecules to the surface of GeSe film and neutralized with holes, which reduces the concentration of carriers and the concentration of holes in GeSe film, thus reducing the conductivity. Our research will contribute to the application of GeSe nanosheets in optoelectronic devices at the atmosphere of oxygen and butane.

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