Half Layer By Half Layer Growth of a Blue Phosphorene Monolayer on a GaN(001) Substrate

Black phosphorene (BlackP), consisting of a vertically corrugated yet single layer of phosphorus atoms, is a latest member of the expanding two-dimensional (2D) materials family with high carrier mobility and immense application potentials. Blue phosphorene (BlueP), an allotrope of BlackP with appealing properties of its own, consists of a more flatly arranged layer of phosphorus atoms. To date, direct growth of either BlackP or BlueP remains a daunting challenge. Using first-principles approaches, here we establish a novel kinetic pathway for fabricating BlueP via epitaxial growth. Our systematic energetic studies reveal that both BlackP and BlueP monolayers can be readily stabilized on Cu(111), Au(111), and GaN(001) substrates. The semiconducting GaN(001) is further shown to be superior for fabricating BlueP, through an intriguing half-layer-by-half-layer (HLBHL) growth mechanism. Within this scheme, the GaN(001) surface is first preferentially covered by a half layer of phosphorus adatoms, followed by the addition of the other half. Once formed, such a BlueP monolayer is thermodynamically stable, as tested using ab initio molecular dynamics simulations. The HLBHL growth mechanism discovered here may enable mass production of high-quality BlueP, and could also be instrumental in achieving epitaxial growth of BlackP and other 2D materials.

Figure 1

Top views of the respective BlackP and BlueP on (a) and (c) Au(111), (e) and (g) Cu(111), (i) and (k) any of the three III-V(001) substrates considered. The corresponding side views are given in the lower panels.

Figure 2

Contrasting thermodynamic stabilities of (a) BlackP and (b) BlueP on GaN(001) after 1 ps and 50 ps AIMD simulations, respectively. The temperature was identically set at 400 K, and the respective initial configurations are shown in Figs. 1 and 1.

Figure 3

Diffusion barriers of a P adatom on (a) pure GaN(001) and (b) a P HL-covered GaN(001). (c) Ehrlich-Schwoebel barrier for a P adatom to climb down the step of pure GaN(001) and P HL-covered GaN(001). In (d), all the diffusion barriers for a P adatom are summarized. IS, TrS, and FS represents the initial state, transition state, and final state, respectively.

Figure 4

(a) Formation energy per P adatom $E_f/N$ as a function of the fraction coverage $\theta$ on GaN(001), where $E_f=-(E_t-E_{\text{sub}})$. The insets (a1) and (a2) give the first and second difference of the formation energy as a function of the fraction coverage $\theta$, respectively. No, D2, TS, and DF2 denote the data obtained without vdW correction, with DFT-D2, DFT-TS, and vdW-DF2 corrections, respectively. (b)–(e) Representative configurations at different P coverages.