Induced out-of-plane piezoelectricity and giant Rashba spin splitting in Janus WSiZ3H (Z = N, P, As) monolayers toward next-generation electronic devices

Abstract

Two-dimensional (2D) piezoelectric nanomaterials have widely been studied recently due to their promise for various applications in technology. Investigation of vertical piezoelectricity will contribute to a deeper understanding of the intrinsic mechanism of piezoelectric effects in the 2D structures. In this paper, we report a first-principle study for the structural, electronic, piezoelectric, and transport properties of new-designed Janus WSiZ3H (Z= N, P, and As) monolayers. The structural stability of WSiZ3H is theoretically confirmed based on the energetic, phonon dispersion, and also elastic analyses. At the ground state, while WSiN3H is an indirect semiconductor, both WSiP3H and WSiAs3H are predicted to be direct semiconductors with smaller bandgaps. When the spin-orbit coupling effects are taken into account, a large valley spin splitting is observed at the K point of WSiZ3H materials. Interestingly, a giant Rashba spin splitting is found in WSiP3H and WSiAs3H with Rashba constant αR up to 770.91 meV Å. Additionally, our first-principles study indicates that Janus WSiZ3H monolayers are piezoelectric semiconductors with high out-of-plane piezoelectric coefficient |d31|, up to 0.15 pm/V, due to the broken mirror symmetry. Besides, with high electron mobilities and also possessing direct band gaps, WSiP3H and WSiAs3H monolayers are favorable for applications in optoelectronics.

Large piezoelectric responses and ultra-high carrier mobility in Janus HfGeZ3H (Z = N, P, As) monolayers: a first-principles study

“…Specifically, the values of e 31 are 0.32 × 10 −10 , 0.14 × 10 −10 , and 0.02 × 10 −10 C m −1 for the HfGeN 3 H, HfGeP 3 H, and HfGeAs 3 H monolayers, respectively. These results reflect that the HfGeN 3 H monolayer has the highest e 31 among the studied monolayers, which is comparable to that of similar Janus structures such as MoGeZ 3 H 55 and WSiZ 3 H. 56 In addition, the out-of-plane piezoelectricity d 31 of HfGeZ 3 H monolayers has a value ranging from 0.01 to 0.09 pm V −1 . The obtained values of d 31 are close to that in the Janus WSiZ 3 H monolayer.…”

“…The obtained values of d 31 are close to that in the Janus WSiZ 3 H monolayer. 56 The above results reveal that 2D Janus HfGeZ 3 H systems are suitable for piezoelectric applications.…”

“…The piezoelectric coefficient e 11 is the largest in the Janus HfGeN 3 H monolayer (2.77 × 10 −10 C m −1 ), while the magnitude of d 11 is the largest in the HfGeAs 3 H monolayer (−1.78 pm V −1 ). These values are smaller than the corresponding piezoelectric coefficients in structurally similar compounds such as MoGeZ 3 H 55 and WSiZ 3 H. 56 More importantly, the out-of-plane piezoelectric coefficients in Janus structures are non-zero, resulting from the breaking of mirror symmetry due to different atoms at the two surfaces of the material. Specifically, the values of e 31 are 0.32 × 10 −10 , 0.14 × 10 −10 , and 0.02 × 10 −10 C m −1 for the HfGeN 3 H, HfGeP 3 H, and HfGeAs 3 H monolayers, respectively.…”

“…28 Very recently, the piezoelectric effect has been reported in other 2D Janus materials, such as γ-Sn 2 XY (X/Y = S, Se, Te) 29 or WSiZ 3 H (Z = N, P, As). 30…”