Computational investigation of electronic, vibrational, and transport properties of silicon phosphide nanoribbons

Two-dimensional (2D) silicon phosphide (SiP) has recently emerged as a promising semiconductor for electronic, optoelectronic, and thermoelectric applications due to its unique electronic and structural characteristics. One-dimensional (1D) nanoribbons (NRs) derived from 2D SiP offer a versatile and scalable platform for device miniaturization and performance enhancement in nanoelectronics. Motivated by their potential, we present a comprehensive first-principles investigation of the structural, electronic, dynamical, and electronic transport properties of SiP-NRs. Specifically, we focus on both bare and hydrogen-passivated armchair (A-NRs, HA-NRs) and zigzag (Z-NRs, HZ-NRs) configurations. Our results reveal that hydrogen passivation effectively suppresses edge reconstructions observed in bare SiP-NRs, thus dynamically stabilizing their structures. Analysis of electronic band structures demonstrates a clear width-dependent oscillatory behavior of the band gap in bare A-NRs, which diminishes significantly upon hydrogen termination. The width-scaled electronic conductance (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msubsup><a:mi>G</a:mi><a:mi>e</a:mi><a:mi>ws</a:mi></a:msubsup></a:math>) of HA-NRs exhibits a decreasing trend with increasing ribbon width, featuring distinct even-odd oscillations for <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>n</b:mi></b:math>-type transport due to subband splitting effects. In contrast, HZ-NRs display notable deviations in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mi>p</c:mi></c:math>-type conductance from their 2D SiP counterpart, particularly at low temperatures (around 100 K), arising from residual localized edge states. However, with increasing width and temperature, transport behavior converges toward that of 2D SiP monolayers, indicating diminishing edge effects. Unlike their <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mi>p</d:mi></d:math>-type counterparts, the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mi>n</e:mi></e:math>-type <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:msub><f:mi>G</f:mi><f:mi>e</f:mi></f:msub></f:math> values of the largest HA-NRs and HZ-NRs increase with the square root of temperature, similar to the <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mi>n</g:mi></g:math>-type conductance trend observed in 2D SiP. This behavior is attributed to the evolution of the electronic transmission function (<h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mi>τ</h:mi><h:mo>(</h:mo><h:mi>E</h:mi><h:mo>)</h:mo></h:mrow></h:math>) from a steplike profile in narrow ribbons to an <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:msup><i:mi>E</i:mi><i:mrow><i:mn>1</i:mn><i:mo>/</i:mo><i:mn>2</i:mn></i:mrow></i:msup></i:math> dependence in wider ribbons, analogous to the 2D counterpart. These findings highlight the significant influence of width and edge termination on the transport characteristics of SiP-NRs and underline their potential as fundamental building blocks for high-performance nanoelectronic and thermoelectric quasi-1D devices.