| Two-dimensional materials show a great prospect in electronics due to their scaling semiconductor into atomic thickness and unique optoelectronic advantages,such as effectively reduce the power consumption and improve the integration of the device,etc.Representing the two-dimensional?2D?materials,though graphene and hexagonal boron nitride have similar atomic structures,there is a large difference in properties.As the alloy of graphene and hexagonal boron nitride?h-BN?,2D hexagonal boron-carbon nitrogen?h-BCN?has high carrier mobility and adjustable band gap,therefore it is an achievable two-dimensional semiconductor with many values.However,it is a tough task for this purpose because of the tendency of easy phase separation in the B-C-N system.In this work,by the methods of molecule-like doping,we dope C atoms into h-BN as well as dope B-N atoms into graphene.We studied the atomic structures and optoelectronic properties of h-BCN.The specific research contents are as follows.1.C atoms doped into 2D h-BN.We construct 35 different carbon molecule-like defect models by permutation and combination.The most feasible C defects?such as dimer and six-fold ring?in h-BN are concluded by comparing the formation energy of every defect.Then we construct non-phase separated h-BCN model by doping these two defects into h-BN.To proving the rationality of this model,we take Mo1-xWxS2with W atoms doped and?BN?1-xCx with independent C atom doped as examples.Through analysis,though the formation energy of non-phase separated model we proposed is relatively higher than the model with independent C atom doped,it can be synthesized under certain experimental conditions?such as electron beam irradiation?.Thus,more models of different C concentration with C dimers or six-fold rings or their mixtures are built.By calculating the imaginary part of dielectric constant in different h-BCN models,we find that the peaks of optic absorb are around 3.5 eV?GGA calculation?under different C concentrations,which shows good light absorb performance.Subsequently,we further analysis their band structures,the density of states as well as the distribution of space charge in CBM and VBM.The results show that the band gaps of h-BN are gradually decreasing with the increasing of C concentration,and the band gaps can be adjusted in the range of 4.67 eV2.92 eV?GGA band gaps,the C concentration is range from 0%14%?.While the CBM and VBM states are mainly derived from the p orbital electrons of C atoms.Therefore,it can be applied to optoelectronic devices,such as solar cells,LEDs,tunable wavelength lasers and so on.2.B-N atoms doped into graphene.We constructed 17 different molecule-like defect structures in graphene using B-N atoms.After calculating,we can obtain several defect structures with the lowest formation energy,such as dimer with B-N atoms and B-N six-member ring.Another B-C-N model with non-phase separated are constructed by these two molecule-like defects,and then we calculate the band gaps of these models.Result shows that band gaps of graphene are gradually opened up with the increasing of B-N concentration,most importantly,the band gap of graphene can be up to 0.6 eV?GGA band gaps?when B-N concentration is 23.4%.We also find the mobility of these models is much higher than the models with C defects in h-BN,so it can be more possible employed into optoelectronic devices.Subsequently,we further analysis the distribution of space charge in CBM and VBM for some h-BCN models,according to the results,the band edge states are mainly derived from the C atoms.Above all,with the method of molecule-like doping,we set about these two tasks around the structure of h-BCN,and try to solve the problem of phase-separated structure.In this paper,we proposed two methods to synthesize non-phase-separated h-BCN,and analyzed their optoelectronic properties respectively.We hope that the above exploration can provide some important enlightenment for the application of two-dimensional BCN semiconductor in the field of optoelectronic devices. |
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