A Computational Study Of Defect Properties In Binary Wide Bandgap Semiconductors Cuprous Iodide And Silicon Carbide

Cuprous iodide（CuI）and 4H silicon carbide（4H-SiC）are two binary wide bandgap semiconductors that have received widespread attention in recent years.They have properties such as simple crystal structure,inexpensive and easily obtainable constituent elements,and good thermal stability,and their bandgap values are within the range of 3.1-3.2 e V.CuI has intrinsic p-type conductivity and high hole mobility,making it suitable for applications in optoelectronics,thermoelectricity,transparent displays,and other fields.SiC boasts advantages such as high-temperature resistance,high-pressure resistance,and high saturation electron drift velocity.These properties make SiC suitable for creating radiation-resistant semiconductors,high electron mobility transistors,and various other electronic devices.At the same time,there are various spin quantum defects in the 4H-SiC crystal structure,making it a hot topic in quantum spin defect research in recent years.Despite the simplicity of crystal structures and constituent elements in CuI and4H-SiC,their defect properties remain inadequately explored,leading to some experimental phenomena related to defects that cannot be explained.For example,the intrinsic CuI crystal exhibits a red light emission peak,but the defect source responsible for this remains unidentified.Similarly,4H-SiC displays multiple unexplained optical and magnetic signal sources with their corresponding defect structures yet to be determined.Furthermore,3C-SiC,an isomer of 4H-SiC with a bandgap value of 2.3e V,also possesses a single-photon source signal of unknown origin.To address these issues,this study focuses on two types of wide bandgap semiconductors,CuI and SiC,employing first-principles calculations to study the defect properties of these two materials.The main research results are as follows:（1）The properties of main point defects and defect clusters in CuI were studied,and the defect type corresponding to the red light emission peak was identified.Based on this,a defect modulation scheme was proposed.There are two main emission peaks in the photoluminescence spectrum characterization of CuI:one is violet radiation（410-430 nm）,which comes from the transition of electrons between bands or copper vacancy defects,while the other is red light（680-720 nm）,the source and mechanism of which are not yet clear.Through first-principles simulation,this study investigated the formation energy,defect energy level,and position and shape of the corresponding emission spectrum for various main point defects and defect clusters.It was found that the intrinsic point defect cluster V_I+Cu_i²⁺is the source of the red light emission peak.The calculation results show that as the chemical conditions change from copper-rich to iodine-rich,the defect concentration decreases significantly,which is consistent with the phenomenon that the radiation intensity in the red light band decreases significantly when the thin film sample is annealed in an iodine-rich environment in experiments.In addition,this study proposes a strategy for controlling the concentration of different defects and related charge carriers in CuI by using chemical growth conditions.This work provides a theoretical basis for understanding the electrical and luminescent properties of CuI and optimizing the performance of materials and devices.（2）In response to the problem of unclear defect structures in near-infrared color center defects in 4H-SiC,this study used first-principles calculations to simulate the properties of color centers and compared them with experimental data to propose defect configurations corresponding to unknown signal sources.In recent years,various optical and microwave resonance signal sources with spin quantum state characteristics have been found in the 1000-1200 nm near-infrared band of 4H-SiC.Four of these signal sources（PL1-PL4）correspond to four dual-vacancy defect configurations,but there are still many signal sources（such as PL5-PL8）whose corresponding defect types remain to be explored.In this study,new defects were constructed based on dual-vacancy color center defects through element substitution.Their electronic spin properties,luminescent properties,and zero-field splitting properties were calculated using first-principles simulations and compared with experimental data to propose color center configurations corresponding to PL5-PL8.The calculation results show that PL5,PL6,and PL7 may be caused by defect clusters formed by oxygen-filling vacancies and dual vacancies,while the source of PL8 may be a defect cluster formed by nitrogen-hydrogen atoms filling vacancies and dual vacancies.This work provides theoretical support for identifying color center configurations in experiments and optimizing spin quantum-state defects.（3）This paper identified the defect type of an unknown single-photon source color center in 3C-SiC.In recent years,a new type of high quantum efficiency single-photon source has been prepared in 3C-SiC,but its defect structure is unknown.Meanwhile,the emission peak wavelength of the single-photon source at different sites exhibits a certain distribution range.Through first-principles simulations,this paper found that the excitation and emission wavelengths of the H_Si^- substitutional defect with negative valence match the experimental data,so it is predicted to be the defect origin of this single-photon source.In addition,this paper studied the effects of stress,dislocations,and other factors on its luminescence properties.The calculation results show that stress causes the luminescence peak of the defect to shift to longer wavelengths,while dislocations cause the luminescence peak to shift to shorter wavelengths.Both may be reasons for the certain distribution range of the emission peak wavelength.This work reveals the defect origin of the single-photon source in 3C-SiC and provides the scientific basis for understanding its luminescence mechanism and improving the properties of the single-photon source.In summary,this paper investigated the defect properties of CuI and SiC using the first-principles calculation method.The findings reveal the presence of numerous intrinsic defect clusters and impurity-related defect clusters within these semiconductor types.The rich physical properties presented by these defect clusters were explored,and various defect origins corresponding to experimental characterization results were proposed.The insights garnered from this research offer a theoretical foundation for regulating defect properties and optimizing semiconductor performance.Consequently,these findings hold the potential to positively impact the development of binary wide-bandgap semiconductors in applications such as light detection,single-photon sources,and spin qubits.