Monolayer H-Si-P Semiconductors: Structural stability, electronic structure, optical properties, and Prospects for photocatalytic water splitting
MMonolayer H-Si-P Semiconductors: Structural stability, electronicstructure, optical properties, and Prospects for photocatalytic watersplitting
Xiaoqin Shu , Jiahe Lin , Hong Zhang School of Mathematics and Physics , Leshan Normal College, Leshan, 614000, China School of science, Jimei University, Fujian,361021,China College of Physical Science and Technology, Sichuan University, Chengdu, 610065, China
Group IV and V monolayers are the promising state-of-the-art 2D materials owing to theirhigh carrier mobility, tunable bandgaps, and optical linear dichroism along with outstandingelectronic and thermoelectric properties. Furthermore, recent studies reveal the stability offree-standing 2D monolayers by hydrogenation. Inspired by this, we systematically predict andinvestigate the structure and properties of various hydrogen saturated silicon phosphide (H-Si-P)monolayers, based on first-principles calculations. According to the results, H-Si-P monolayersbelong to indirect bandgap semiconductors with a highly stable structure. Their bandgaps andband edge positions assessed using accurate hybrid functional are shown to be effectively adjustedby applying a biaxial strain. Furthermore, the absorption spectra of these monolayers, simulated inthe context of time-dependent density functional theory, exhibit their excellent potential for solarenergy conversion and visible-light-driven photocatalytic water splitting. In this respect, this workprovides valuable guidance for finding more 2D semiconductors and nanostructures fornanoelectronic and optoelectronic applications, as well as for photocatalytic water splitting.Key words: 2D monolayers, 2D semiconductors and nanostructures, first-principlescalculations; photocatalytic water splitting. * Corresponding author.
E-mail address : [email protected] ( H. Zhang ) . IntroductionTwo-dimensional (2D) materials haveattracted increasing interest with respect totheir integration into optoelectronic devices.Among them, graphene, MoS , MoSe and soon [1-8], due to the tunable band gap that isthe basis for broadband photoresponse.However, the in-plane isotropic structure ofthese materials impedes their application inpolarization-sensitive photodetectors. In thisrespect, since 2014, tremendous attention hasbeen paid to a novel 2D layeredsemiconductor material, called blackphosphorus (BP). Its in-plane anisotropicphysical properties along zigzag and armchairdirections along with prominent carriermobility and thickness-dependent direct bandgap allowed BP to be considered as promisingnot only in polarization-sensitivephotodetectors, but also in transistors,photonic and optoelectronic appliances,sensors, batteries, catalysis, and many otherapplications [9-17]. Meanwhile, the extensivedevelopment of BP was hampered by itsinstability under ambient conditions, as wellas by the lack of techniques for producinglarge-area and high-quality 2Dnanofilms[18,19].In this regard, attempts were made todiscover analogues with improvedcharacteristics, leading to group IV-V 2Dsemiconductors, such as GeP [20] and GeAs[21] materials, whose high in-planeanisotropic properties have become a hot topicof modern research. Among these, particularattention is drawn to orthorhombic siliconphosphides (o-SiP, mm2 point group), forwhich various theoretical calculations predicta widely tunable band gap (from 1.69 to 2.59eV) and high carrier mobility similar to that ofblack phosphorus [22]. However, there is stilla few experimental works that could bringnew information on the optical and electronicproperties, especially on the in-plane anisotropic characteristics of o-SiP. One rareexample is a study of Li et al. , who haveexperimentally confirmed that o-SiP is anexcellent optoelectronic 2D material with alarge band gap (1.71 eV), high mobility (2.034× 10 cm ·V -1 ·s -1 ), and fast photoresponse.[23].Nevertheless, the in-plane anisotropy of o-SiP,being of importance for state-of-the-artdevices, such as thin-film polarizers,polarization sensors, and plasmonic devices,has still remained beyond of the scope ofmany researchers.In this work, we design three hydrogensaturated SiP monolayers, called H-Si-P.Depending on the hydrogen position, they areHPSi, HSiP, and HSiPbp structures,respectively. HPSi means that hydrogen atomsare added to phosphorus atoms in the upwarddirection. HSiP refers to a structure wherehydrogen atoms are attached to silicon atomsin the upward direction. HSiPbp indicates thathydrogen atoms are linked to silicon atoms inboth the upward and downward directions.The HPSi and HSiP monolayers possess aspace-group symmetry P M , whereas
HSipbp monolayer is described by a PMN space group. Special attention is paid to atheoretical study of the optical and electronicproperties of these monolayers simulatedthrough density functional theory (DFT) . Inparticular, their phonon spectra and cohesiveenergies are calculated to prove a highly stablestructure of these compounds. Theinvestigation of band gaps and band edgepositions of monolayer H-Si-Ps exhibits theirsemiconductor properties, which even can betuned by applying the mechanical biaxialstrains. The optical absorption spectra of themonolayer compounds reveal an increase inthe potential efficiency of solar energyconversion and water splitting, proving thatthese nanostructures are promising for watersplitting in a visible-light region.. Computational detailsFor periodic H-Si-P monolayer, theoptical and electronic properties weresimulated in the context of the ab initiodensity functional theory (DFT) using theCASTEP package [24]. During calculations,the norm-conserving pseudopotentials and theplane wave energy cutoff of 720 eV wereemployed to relax the structure models alongwith the band structures via the generalizedgradient approximation (GGA) expressed bythe Perdew-Burke-Ernzerhof (PBE) functional[25]. The structures, including the primitivecells of monolayer H-Si-P, were exposed torelaxation until the forces were smaller than0.01 eV/Å and the energy tolerances were lessthan 1×10 -7 eV per atom. A vacuum layer of23 Å was used to avoid interactions betweenneighboring layers. The k-point sampling ofthe Brillouin zone with 6×6×1 for monolayerHPSi and HSiP, with 8×8×1 for HSiPbp wasperformed by adopting the Monkhorst-Packscheme[26]. The phonon dispersions ofmonolayer H-Si-P were calculated by thelinear response method [27]. The bandstructures, density of states, and opticalproperties were evaluated by theHeyd-Scuseria-Ernzerhof screened hybridfunctional (HSE06) [28].For monolayer nanostructures, thecollective plasmonic excitations weresimulated in the direction parallel to thenanostructure plane using the time-dependentdensity functional theory (TDDFT) on the basis of OCTOPUS real-space TDDFT code[29]. The dangling bonds at the edges werepassivated by hydrogen atoms using theTroullier–Martins pseudopotentials [30] toelucidate the impact of different edge statesand dimensional confinement on the collectiveplasmonic excitations of H-Si-P structures.Reparametrized PBE (Perdew, Burke andErnzerhof)[25] for the van der Waalsinteractions for the exchange potential andcorrelation potential used in both the groundstate and excited-state calculations. To obtainthe linear optical absorption spectra of thestudied structures, their initial states wereexcited by providing a smallmomentum ( ) ( ) kick E t E t to the electrons atassuming the time-propagating Kohn–Shamwave functions. The information of theexcitations was deduced from thedipole-strength function, and the excitationspectrum was obtained from the Fouriertransformation of the dipole strength. Thesimulation zone was defined by assigning asphere centered around each atom with aradius of 7 Å and a uniform mesh grid of 0.3Å. In a real-time propagation, the Kohn–Shamwave function evolved for typically 6000steps with a time step of 0.003 ℏ / eV. Theatoms were fixed in the XY plane of theCartesian coordinate system. The zigzag edgeof the nanostructure was assumed to beperpendicular to the X-axis, while thearmchair edge was parallel to the X-axis.3. Results and discussion IG. 1. (a), (e) and (h) Top views of the monolayer HPSi, HSiP, and HSiPbp structures, respectively, marked withtheir structural parameters. (b), (f) and (i) Side views of the monolayer HPSi, HSiP, HSiPbp structures, respectively.The gold, purple, and white spheres stand for silicon, phosphorus, and hydrogen atoms, respectively. (c), (g) and (j)Brillouin zones and main high symmetric points of the monolayer HPSi, HSiP, and HSiPbp structures, respectively.(d) Illustration of photocatalytic water splitting. The successful water splitting using a single photocatalyst isachieved through a properly aligned bandgap of the semiconductor with respect to the redox potentials of water-4.44 eV and -5.67 eV,respectively.
Three different structures, so-called HPSi,HSiP, and HSiPbp, were simulated. Their fullstructural relaxations enabled one to obtain thestructural parameters, including latticeconstants, bond length, layer height, and bondangles as shown in Figure 1. Thecorresponding values of the parametersevaluated for the above structures aresummarized in Table I. In order to study thestability of H-Si-P monolayers, their cohesiveenergies along with the phonon dispersionswere calculated using the equations below: tot Si P Hcoh E E E EE (1) tot Si P Hcoh
E E E EE (2)Equation (1) was used for HPSi and HSiPstructures , and Eq. (2) was applied forHSiPbp. Here, coh E is the total energy ofH-Si-P monolayer and Si E , P E , H E are theground state energies of Si, P, and H freeatoms, respectively, calculated in neglectingthe interactions between the neighboringatoms in a cubic cell with a lattice constant of20 Å. As seen in Table 1, the cohesive energies of HPSi, HSiP and HSiPbp are foundto be -4.498, -4.751, and -4.740 eV,respectively. The high enough cohesiveenergies of the three monolayer structuresevidence the high stability of H-Si-Pmonolayers.The properties of phonons can bedescribed using a harmonic approximationbased on the knowledge of just onefundamental quantity, the force constantsmatrix: ( ) u ( ) ED R R u R R ( ) (3)
Here refers to the displacement of a givenatom and E is the total energy in theharmonic approximation. This force constantsmatrix (or Hessian matrix) can also berepresented in reciprocal space and the resultis commonly referred to as the dynamicalmatrix:
1( ) ( ) exp( ) RR D q D R iqRN (4) Classical equations of motion can bewritten in the language of dynamical matrices,s an eigenvalue problem. Each atomicdisplacement is described in the form of planewaves: ( ( ) ) ( , ) i qR q t u R t e (5) where the polarization vector of each mode, ,is an eigenvector with the dimension of 3N ofthe eigenvalue problem: ( ) ( ) M q D q (6)
The dependence of the frequency, , on thewave vector is known as the phonondispersion.Figure 2 displays the phonon banddispersions of HPSi, HSiP, and HSiPbpstructures along the high symmetric points oftheir Brillouin zones with respect to Figures1(g)-1(i). Here, the stability of the calculatedphonon dispersions at a lack of soft modes andthe linear dispersion relation of the acousticbranch around the G point indicates theoutstanding kinetic stability of the simulatedmonolayer H-Si-P structures. TABLE I. Optimized geometries and cohesive energies of H-Si-P (HPSi, HSiP, HSiPbp ) monolayers, obtainedusing DFT with a PBE exchange-correlation functional.
Structure Spacegroup Cohesiveenergy(eV/atom) Lattice constant( Å ) a b Bondlength( Å ) l Layerheight( Å ) h HPSi
P3M1 -4.498 3.5469 3.5469 2.323 1.09HSiP
P3M1 -4.751 3.5427 3.5469 2.269 1.09HSiPbp
PMN21 -4.740 3.5345 5.5693 2.261 1.38
FIG. 2. (a)-(c) Phonon band dispersions of HPSi, HSiP, and HSiPbp structures.
Figure 3 depicts the band structures ofmonolayer H-Si-P systems, calculated usingthe HSE06 hybrid functional. Their bandgapswere found to be 2.74, 3.325, and 3.749 eV forHPSi, HSiP, and HSiPbp, respectively. Suchthe wide band gaps of the studied 2Dmaterials allow one to refer them to 2Dsemiconductors that are suitable forapplications in high-power electronic devices, field emission appliances, and optoelectronictools operating under UV or visible lightconditions. Furthermore, the bandgaps exhibitthe indirect behavior. For HPSi, the VBmaximum (VBM) lies at K point, and the CBminimum (CBM) occurs along the G-Mdirection. For HSiP, the VBM intersects the Gpoint, and the CBM crosses over the M point.For HSiPbp, the VBM arises along the Y-Girection, and the CBM lies at G point.
FIG. 3 (a)-(c) Band structures of monolayer HPSi, HSiP, and HSiPbp, respectively. The VBM is set to zero by thered dash lines.FIG. 4. (a)–(c)
The total densities of states (TDOS) and partial densities of states (PDOS) of HPSi,HSiP, and HSiPbp , respectively.
In order to understand the contribution ofdifferent orbitals to the electronic states andthe bonding characteristics of monolayerH-Si-P, the total densities of states (TDOS)and partial densities of states (PDOS) werecalculated for monolayer H-Si-P. Figure 4displays the total densities of states (TDOS)and partial densities of states (PDOS)calculated for monolayer H-Si-P As seen inFigure 4, TDOS of all monolayer compounds,considered in this work, exhibit multiple vanHove singularities over the entire energy range,which is consistent with the 2D nature of amonolayer SiP material. In turn, the PDOS ofmonolayer compounds reveal thecontributions from both the s and p orbitals ofSi and P near the Fermi level. Obviously, theeffects from the p orbitals of Si and P to theTDOS are much more pronounced than thosefrom the s orbitals. Such a predominance ofthe p orbitals is due to the sp -like bonding of P atoms and sp -like bonding ofgroup Ⅴ forming the monolayer H-Si-P, andthis feature is always observed in group IVdiamond-like structures and monolayerhoneycomb systems of group III elements. Athorough analysis of PDOS plots reveals thatthe state closest to the VBM of HPSioriginates from the p orbitals of Si atoms,whereas the states closest to the VBM of HSiPand HSiPbp arise from the p orbitals of Patoms. As for the states closest to the CBM,these refer to the p orbitals of Si atoms.Additionally, the specific distribution ofVBMs and CBMs in the monolayercompounds is beneficial for the separation ofphotogenerated electron-hole pairs, thusreducing their recombination and increasingthe photocatalytic activity [31].To determine the alignment of the CBMand VBM energies, the work functions ofmonolayer H-Si-P were calculated by usingthe HSE06 functional. Figure 5 displays theBM and VBM energy levels with the redoxpotentials of water splitting. To make asemiconductor promising for water splitting,both the reduction and oxidation potentialsmust be located inside the bandgap. Asshown in Figure 5, their values are found to be / H H V = 4.44 eV and / OH O V = 5.67 eV,respectively, which are obviously within theband gaps of the studied materials, therebyrevealing the energetically favorable redoxprocess for these. In this respect, thesemonolayer materials can be deemed to be thecandidates for photocatalytic water splitting.However, since the bandgaps of HSiP andHSiPbp monolayer compounds are within theUV light energy range, this impedes theirapplication for visible-light-inducedphotocatalytic splitting water. Moreover, eventhough the theoretical calculations predict thesuitability of monolayer H-Si-P systems forphotocatalytic water splitting in the vacuum,the situation may change when placing themin a liquid water environment. Therefore,further investigations are necessary tounderstand the band structure behavior ofthese 2D materials in water. FIG. 5. Band edge positions of monolayer HPSi, HSiP,and HSiPbp relative to the vacuum level at a zerostrain, calculated using the HSE06 functional. Thestandard redox potentials for water splitting are shownfor comparison. FIG. 6.Cohesive energies for HPSi, HSiP, and HSiPbpvs. biaxial strain . Strain is inevitable in real systems due tothe synthetic and application environments.Many experimental and theoretical studies[32-36] have shown that applying mechanicalstrain to the sample is a powerful method formodulating its band structure and the opticalproperties. In this respect, monolayer H-Si-Psystems were subjected to mechanical tensileand compressive biaxial strains to monitor theevolution of their band structures and opticalproperties. The mechanical biaxial strain wassimulated by freezing one of the latticeconstants, as follows: / a a a ,where a is the optimized lattice constantand a is the lattice parameter along thestrain direction. The positive and negativevalues of were attributed to tensile andcompressive strain, respectively. Figure 6displays the cohesive energy as a function ofstrain for the H-Si-P systems within astrain range from -10% to 10% at a spacing of1%. According to these plots, the structuresunder consideration remain highly stableunder the applied loads, even though thestability of stretched and compressedmonolayers is weaker than that before strain.Furthermore, the HSiP and HSiPbp systemsare obviously more stable than HPSi.Figure 7 depicts the bandgaps versusstrain for the H-Si-P structures within thesame strain range, as in Figure 6. As seen inFigure 7(a), the band gaps of all the studied-Si-P monolayers exhibit the identical trend,increasing in a quasi-linear manner to a certain value and then linearly decreasing withincreasing . Special attention is drawn tothe band gap variation for a monolayerHSiPbp (shown with a blue line in Figure.7(a)), where two linear tendencies (a risefollowed by a drop) of band gap values areclearly observed. This can be interpreted, asfollows. At > -1%, there is an increase inthe distance between the Si and P atoms,which makes the overlap integral of the wavefunctions between them decrease, leading to adecrease of their bandgaps. At < -1%, thedistance between the neighboring Si atoms inthe same sublayer becomes so close that theoverlap integral of the wave functions for theinner electrons of these Si atoms increases,causing a decrease in their bandgaps with | | increasing. It is thus clear that thebandgaps of the monolayer H-Si-P have alinear response within a certain biaxial tensilestrain range, which means the prospects oftheir application in mechanical sensors.ForHPSi, the bandgaps within a range of -10% < < 10% are found to vary from 1.628 to2.056 eV, respectively, thus meetingrequirements for the photocatalytic watersplitting under visible light. For HSiP, the bandgaps within a range of -10% < < -3 %are found to vary from 1.866 to 3.136 eV,respectively, and when = 8%, 9% and 10%,their bandgaps are 3.111, 2.857 and 2.613eV,respectively. For HSiPbp, the bandgaps withina range of -10% < < -5 % are found tovary from 1.862 to 3.129 eV, respectively andbandgaps within a range of 5 % < < 10 %are found to vary from 3.117 to 2.556eV,respectively. In this respect, the bandgaps ofall presented 2D materials cover the visiblelight range, meaning that thesesemiconductors exhibit the high lightutilization rate.The effect of strain on the band edgepositions of monolayer compounds waselucidated by determining the correspondingCBM and VBM from the relaxedconfigurations by calculating the workfunctions. Figure 7(b) displays the band edgepositions of HPSi, HSiP, and HSiPbpundergoing biaxial strain. Therefore, Figure 7is shown to provide useful guidance for tuningthe bandgaps along with CBM and VBMlevels of monolayer compounds to maximizethe solar energy conversion efficiency. For thisreason, data presented in Figure 7 were furtherused to calculate the absorption spectra ofmonolayer H-Si-P to investigate their sunlightutilization. FIG. 7. (a) Bandgaps and (b) band edge positions of HPSi, HSiP, and HSiPbp vs. biaxial strain.IG. 8.Evolution of absorption spectra of (a) HPSi, (b) HSiP, and (c) HSiPbp systems with biaxial strain below6eV.
The absorption spectra of 2D monolayerstructures were calculated in assuming thein-plane polarized light. First, the frequency-dependent dielectric function ( ) ( ) ( ) i was found. Then theabsorption coefficient was evaluated as afunction of photon energy according to thefollowing expression [37]: ( )4( ) [ ]2 eE hc (7)Figure 8 shows the absorption spectra of HPSi, HSiP, and HSiPbp under biaxial strain,simulated within a range of below 6eV. Noabsorption resonance peaks arise within avisible (3.3–1.7 eV) range. As is known, aperiodic 2D graphene structure manifests itselfby a resonance peak around 5.0 eV in itsabsorption spectrum [38-40]. However, in thecase of 2D graphene nanostrctures, theboundary effect leads to the absorption peaksplitting in the low energy region [41,42]. Inthis respect, one can assume the samesituation for the monolayer H-Si-Pnanostructures under consideration.
FIG. 9 Top and side views of the monolayer (a) and (b) for HPSi,(c) and (d) for HSiP, (e) and (f) for HSiPbpnanostructures, respectively, and their structural parameters. The HPSi nanostructure is composed of 27 silicon, 27phosphorus and 27 hydrogen atoms. The HSiP nanostructure is composed of 25 silicon, 25 phosphorus and 34hydrogen atoms in HSiP nanostructure. The HSiPbp nanostructure is composed of 27 silicon, 27phosphorus and 37hydrogen atoms. In all structures, the dangling bonds at the edges are passivated by hydrogen atoms.
In order to confirm or deny this suggestion,the absorption peculiarities were calculated forthe monolayer H-Si-P nanostructures below 9eV, shown in Figure 10. For this, the collective plasmonic excitations in the monolayer H-Si-Pnanostructures were investigated using thetime-dependent density functional theory(TDDFT) [28].The linear optical absorptionpectra of the systems were obtainedfollowing a scheme proposed by Yabana andBertsch [43], where their excitationfrequencies were determined from themomentum ( ) of the electron. The latter wasachieved by transforming the ground-statewave functions propagating in some (finite)time: ( , ) ( , 0) r r i zi i t e (8) The spectra could then be calculated from theexpression of the dipole strength functionpresented below:
2( ) ( ) S , (9) where ( ) is the dynamical polarizabilitydescribed by the Fourier transform of thedipole moment of the system ( ) d t as
1( ) [ ( ) (0)] i t dte d t d (10) Using this definition, theThomas-Reiche-Kuhn sum rule for thenumber of electrons ( N ) is given by theintegral: ( ) N d S (11)
Figure 10 shows the optical absorptionspectra of monolayer H-Si-P systems,simulated using Eq. (5). In comparison withspectra in Figure 8, those in Figure 10 wereextended toward the infrared (below 1.7 eV)region, where it observes the absorptionsplitting for all the studied H-Si-P systems byanalogy with a monolayer graphenenanostructure, which is due to the finite sizeeffects[39,40]. Furthermore, the absorptionspectrum of the graphene nanostructure is alsoknown to depend on the edge (zigzag orarmchair) configuration [39,40]. In this regard,the absorption spectra in Figure 10 were simulated with respect to an impulseexcitation polarized in the x -axis and y -axis directions, where the x -axiscorresponded to the armchair edge directionand the y -axis was referred to a zigzag edge.Obviously that changing the edge directionleads to the pronounced alterations in theoptical absorption spectra of all simulatedsystems, which are especially manifestedbelow 4 eV. When the impulse excitation ispolarized in the armchair edge direction( x axis) , the absorption peaks of HPSi aremainly located in the vicinity of the energyresonance points at 0.86, 1.51, and 2.53 eV;the absorption peaks of HSiP arise at 1.02,1.53, 2.23, 2.88, and 3.89 eV, and those ofHSiPbp are observed at 0.41, 1.37 and 2.62 eV.In the case of the impulse excitation polarizedin the zigzag edge direction ( y axis), theabsorption peaks of HPSi emerge at 0.58, 1.16and 1.98 eV; those of HSiP appear at 0.94,1.48, 2.59, and 3.24 eV, and the absorptionsignatures of HSiPbp are found at 0.96, 1.64,2.46 and 3.1 eV. The energy resonance pointswhich are below 1.6 eV refer to IR radiation.Those that are between 1.6 eV and 3.2 eV refer to visible light. Those that are higherthan 3.2 eV refer to ultraviolet light FIG. 10. The absorption spectra of HPSi, HSiP, andHSiPbp monolayer nanostructures to an impulseexcitation polarized in the (a) x axis and (b) y axisdirections below 6 eV. The inset in FIG. 10(b) showsa close-up view of the absorption spectra below 4 eV.IG. 11. Fourier transforms of the induced chargedensity of (a) HSiPbp and (b-d) HSiP nanostructures.The polarization direction is set along the armchairedge at energy resonance points of (a) 1.37 eV, (b)2.23 eV, and (c) 2.88 eV and along the zigzag edgedirection at energy resonance point of (d) 1.48 eV. To elucidate the mechanism governingthe behavior observed in the opticalabsorption spectra within the low-energyrange for all the simulated structures, thespatial dependence of the induced chargeresponse was analyzed at the resonancefrequencies obtained from the time evolutionin a plane. For this, the induced charge planewas assumed to be parallel to the grapheneplane and the vertical distance between the topatomic layer of the nanostructure and theinduced charge density plane was estimated tobe 0.9 Å. The low-energy resonances weresuggested to be localized at the boundaryregion. The induced charge density profilesfor these plasmonic resonance points exhibiteda dipole-like character. Moreover, thelower-energy plasmons follow the long-rangecharge transfer plasmon (CTP) modeattributed to the electronic motion along thedirection in which electrons can propagatethrough longer distances. Figure 11 shows theFourier transforms of the induced chargedensities of HSiPbp and HSiP nanostructures. The polarization direction was set along thearmchair edge at energy resonance points of1.37 eV for HSiPbp nanostructure and at 2.23and 2.88 eV for HSiP monolayer, as wellalong the zigzag edge direction at energyresonance points of 1.48 eV for HSiPmonolayer. Compared with periodic systems,the selected nanostructures display the highlytunable polarization-dependent enhancedplasmon resonance in a wide frequency region,which would be useful for water splitting ininfrared and visible light regions. . ConclusionsIn summary, monolayer HPSi, HSiP, andHSiPbp were theoretically studied based onfirst-principles calculations. The calculationsof the phonon spectra and cohesive energiesrevealed the high stability of the monolayerH-Si-P structures. According to the bandgapsand band edge simulated using the accuratehybrid functional, all the three monolayerstructures belong to indirect bandgapsemiconductors that were shown to be suitablefor photocatalitic water splitting under visible(HPSi) and ultraviolet light (HSiP and andHSiPbp). Furthermore, their bandgaps andband edge positions were found to beeffectively adjusted by applying a biaxialtensile or compressive strain. Finally, theability to use the simulated H-Si-P monolayersfor light-induced photocatalytic water splittingwas studied via the modeling of their opticalabsorption spectra without strain and underthe ultimate biaxial tensile strain. The absenceof absorption peaks within a visible-lightrange led to a need to calculate the absorptionspectra of these nanostructures using aTDDFT method, which exhibited a series ofabsorption splitting within a visible range. Inthis respect, the simulated 2D nanostructureswere shown to have excellent potential forsolar energy conversion andvisible-light-driven photocatalytic waterplitting. Thus, this work provides valuableguidance for discovering the new 2Dsemiconductors and nanostructures fornanoelectronic and optoelectronic devices, aswell as for potential photocatalytic watersplitting applications.Acknowledgments Xiaoqin Shu and JiaheLin contribute equally to the article, XiaoqinShu and Jiahe Lin are co-first authors of the article.Hong Zhang acknowledges financial support from theNational Natural Science Foundation of China (GrantsNo. 11474207) and National Key R&D Program ofChina (2017YFA0303600); Xiaoqin Shuacknowledges scientific research project of LeshanNormal University (No. XJR17007, and LZDP012and DGZZ202009 ) , Key Research Project of LeshanScience Technology Bureau (No.20GZD036). JiaheLin acknowledges the Foundation from Department ofScience and Technology of Fujian Province (China,Grant No. 2019L3008) , the Foundation fromDepartment of Science and Technology of FujianProvince (China, Grant No. 2020J05147). References [1] Y. H. Chang, W. Zhang, Y. Zhu, Y. 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