GaS/Mg(OH)_(2)异质结电子结构的第一性原理研究

First-principles study on electronic structure of GaS/Mg(OH)_2 heterostructure

基于第一性原理计算方法研究了GaS/Mg(OH)_(2)异质结的稳定性、电子和光学性质.结果表明,GaS/Mg(OH)_(2)异质结具有较小的晶格失配率,负的结合能和热力学稳定性而容易构建.异质结的带隙有效降低至2.021 eV,而且具有Type-Ⅱ型能带结构,有利于光生电子-空穴对的空间分离.层间电荷转移诱导的内建电场进一步促进载流子的分离,同时有助于抑制层间电荷的复合.在双轴应变下,异质结的导带最小值和价带最大值的位置分别产生了不同程度的平移,导致带隙发生显著的变化,变化量达到了0.5 eV.而且在拉伸应变下,异质结由间接转变为直接带隙半导体,同时异质结仍保持Type-Ⅱ型能带结构.此外,应变还可以有效地调控异质结的带边位置与水分解的氧化还原电位相匹配(pH=0—7).光吸收谱显示异质结具有较强的光吸收性能,尤其在拉伸应变为3%时,光吸收发生了明显的红移.这些结果表明,GaS/Mg(OH)_(2)异质结具有可调的电子性能而在光电领域有着广阔的应用前景.

Constructing Type-Ⅱheterostructure is an effective scheme to tailor the electronic structure and improve the application performance.Motivated by recently successful syntheses of Mg(OH)_(2)and GaS monolayers,we investigate the stability,electronic,and optical properties of GaS/Mg(OH)_(2)heterostructure by using the density functional theory method.The calculated results show that GaS/Mg(OH)_(2)heterostructure is easily constructed due to its small lattice mismatch,negative binding energy,and thermodynamic stability.Compared with monolayer materials,the GaS/Mg(OH)_(2)heterostructure has a band gap that effectively decreases to 2.021 eV and has Type-Ⅱband structure,facilitating the spatial separation of photo-generated carriers where electrons are localized in the GaS and holes reside in the Mg(OH)_(2)monolayers.The built-in electric field induced by the interlayer charge transfer points from GaS to Mg(OH)_(2)monolayer,which can further improve the separation and suppress the recombination of electron-hole pairs.Under the biaxial strain,the valance band maximum and conduction band minimum of GaS/Mg(OH)_(2)heterostructure shift in the downward direction to different extents,resulting in obvious change of band gap,with the change reaching about 0.5 eV.Furthermore,the band structure of GaS/Mg(OH)_(2)heterostructure can be transformed from indirect band gap semiconductor into direct band gap semiconductor under the tensile strain,while GaS/Mg(OH)_(2)heterostructure maintains Type-Ⅱband structure.Additionally,the band edge positions of GaS/Mg(OH)_(2)heterostructure can also be effectively adjusted to cross the redox potentials of water decomposition at pH=0-7.The light absorption spectra show that GaS/Mg(OH)_(2)heterostructure has stronger light absorption capability than the constituent monolayers.Especially,the light absorption has an obvious redshift phenomenon at a tensile strain of 3%.These findings indicate that the GaS/Mg(OH)_(2)heterostructure has a wide range of applications in the field of optoelectronics due to the tunable electronic properties,and also provides some valuable insights for future research.