Limits...
High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus.

Qiao J, Kong X, Hu ZX, Yang F, Ji W - Nat Commun (2014)

Bottom Line: The monolayer is exceptional in having an extremely high hole mobility (of order 10,000 cm(2) V(-1) s(-1)) and anomalous elastic properties which reverse the anisotropy.Light absorption spectra indicate linear dichroism between perpendicular in-plane directions, which allows optical determination of the crystalline orientation and optical activation of the anisotropic transport properties.These results make few-layer BP a promising candidate for future electronics.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Renmin University of China, Beijing 100872, China [2] Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing 100872, China [3].

ABSTRACT
Two-dimensional crystals are emerging materials for nanoelectronics. Development of the field requires candidate systems with both a high carrier mobility and, in contrast to graphene, a sufficiently large electronic bandgap. Here we present a detailed theoretical investigation of the atomic and electronic structure of few-layer black phosphorus (BP) to predict its electrical and optical properties. This system has a direct bandgap, tunable from 1.51 eV for a monolayer to 0.59 eV for a five-layer sample. We predict that the mobilities are hole-dominated, rather high and highly anisotropic. The monolayer is exceptional in having an extremely high hole mobility (of order 10,000 cm(2) V(-1) s(-1)) and anomalous elastic properties which reverse the anisotropy. Light absorption spectra indicate linear dichroism between perpendicular in-plane directions, which allows optical determination of the crystalline orientation and optical activation of the anisotropic transport properties. These results make few-layer BP a promising candidate for future electronics.

No MeSH data available.


Optical absorption spectra.(a,b) Optical absorption spectra of few-layer BP for light incident in the c (z) direction and polarized along the a (x) and b (y) directions, respectively. Black dashed lines show an approximate linear fit used to estimate the band edges for the first absorption peak, which are highly anisotropic between x and y. The band edge drops rapidly with sample thickness for x (from 1.55 eV for the monolayer (red) to 0.60 eV for five layers (orange)) but only slightly for y (from 3.14 eV to 2.90 eV). (c) Schematic illustration of a proposed experimental geometry to determine the orientation of few-layer BP structures using optical absorption spectroscopy, and thus to utilize the anisotropic electronic properties of BP. The light is linearly polarized in a chosen orientation and near-normally incident on the sample. The sample should be rotated to identify the a or b direction by monitoring the absorption signal, after which the source and drain electrodes, denoted as ‘S’ and ‘D’ respectively, may be deposited to fabricate an FET device.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4109013&req=5

f3: Optical absorption spectra.(a,b) Optical absorption spectra of few-layer BP for light incident in the c (z) direction and polarized along the a (x) and b (y) directions, respectively. Black dashed lines show an approximate linear fit used to estimate the band edges for the first absorption peak, which are highly anisotropic between x and y. The band edge drops rapidly with sample thickness for x (from 1.55 eV for the monolayer (red) to 0.60 eV for five layers (orange)) but only slightly for y (from 3.14 eV to 2.90 eV). (c) Schematic illustration of a proposed experimental geometry to determine the orientation of few-layer BP structures using optical absorption spectroscopy, and thus to utilize the anisotropic electronic properties of BP. The light is linearly polarized in a chosen orientation and near-normally incident on the sample. The sample should be rotated to identify the a or b direction by monitoring the absorption signal, after which the source and drain electrodes, denoted as ‘S’ and ‘D’ respectively, may be deposited to fabricate an FET device.

Mentions: We have also predicted the optical absorption spectra of few-layer BP systems by computing the dielectric function. Two absorption spectra are shown in Fig. 3a,b for light incident along the z direction and linearly polarized in the x and y directions, respectively; while the results for incident light polarized in the z direction may be found in Supplementary Fig. 4. These results demonstrate a strong linear dichroism: for a dielectric polarization in the x direction, the band edge of the first absorption peak is found at the bandgap and thus falls rapidly with the thickness of the sample (Fig. 3a). By contrast, with y-polarized light this peak is found at 3.14 eV in the monolayer and its position falls only slightly with thickness, remaining at 2.76 eV in bulk BP (Fig. 3b). From the symmetries of the wavefunctions in Fig. 2g, clearly the (odd) dipole operator connects the VB and CB states for x-polarization, allowing the direct-bandgap process, but this is symmetry-forbidden for y-polarization and the transition occurs between VB and CB states elsewhere in the BZ.


High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus.

Qiao J, Kong X, Hu ZX, Yang F, Ji W - Nat Commun (2014)

Optical absorption spectra.(a,b) Optical absorption spectra of few-layer BP for light incident in the c (z) direction and polarized along the a (x) and b (y) directions, respectively. Black dashed lines show an approximate linear fit used to estimate the band edges for the first absorption peak, which are highly anisotropic between x and y. The band edge drops rapidly with sample thickness for x (from 1.55 eV for the monolayer (red) to 0.60 eV for five layers (orange)) but only slightly for y (from 3.14 eV to 2.90 eV). (c) Schematic illustration of a proposed experimental geometry to determine the orientation of few-layer BP structures using optical absorption spectroscopy, and thus to utilize the anisotropic electronic properties of BP. The light is linearly polarized in a chosen orientation and near-normally incident on the sample. The sample should be rotated to identify the a or b direction by monitoring the absorption signal, after which the source and drain electrodes, denoted as ‘S’ and ‘D’ respectively, may be deposited to fabricate an FET device.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4109013&req=5

f3: Optical absorption spectra.(a,b) Optical absorption spectra of few-layer BP for light incident in the c (z) direction and polarized along the a (x) and b (y) directions, respectively. Black dashed lines show an approximate linear fit used to estimate the band edges for the first absorption peak, which are highly anisotropic between x and y. The band edge drops rapidly with sample thickness for x (from 1.55 eV for the monolayer (red) to 0.60 eV for five layers (orange)) but only slightly for y (from 3.14 eV to 2.90 eV). (c) Schematic illustration of a proposed experimental geometry to determine the orientation of few-layer BP structures using optical absorption spectroscopy, and thus to utilize the anisotropic electronic properties of BP. The light is linearly polarized in a chosen orientation and near-normally incident on the sample. The sample should be rotated to identify the a or b direction by monitoring the absorption signal, after which the source and drain electrodes, denoted as ‘S’ and ‘D’ respectively, may be deposited to fabricate an FET device.
Mentions: We have also predicted the optical absorption spectra of few-layer BP systems by computing the dielectric function. Two absorption spectra are shown in Fig. 3a,b for light incident along the z direction and linearly polarized in the x and y directions, respectively; while the results for incident light polarized in the z direction may be found in Supplementary Fig. 4. These results demonstrate a strong linear dichroism: for a dielectric polarization in the x direction, the band edge of the first absorption peak is found at the bandgap and thus falls rapidly with the thickness of the sample (Fig. 3a). By contrast, with y-polarized light this peak is found at 3.14 eV in the monolayer and its position falls only slightly with thickness, remaining at 2.76 eV in bulk BP (Fig. 3b). From the symmetries of the wavefunctions in Fig. 2g, clearly the (odd) dipole operator connects the VB and CB states for x-polarization, allowing the direct-bandgap process, but this is symmetry-forbidden for y-polarization and the transition occurs between VB and CB states elsewhere in the BZ.

Bottom Line: The monolayer is exceptional in having an extremely high hole mobility (of order 10,000 cm(2) V(-1) s(-1)) and anomalous elastic properties which reverse the anisotropy.Light absorption spectra indicate linear dichroism between perpendicular in-plane directions, which allows optical determination of the crystalline orientation and optical activation of the anisotropic transport properties.These results make few-layer BP a promising candidate for future electronics.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Renmin University of China, Beijing 100872, China [2] Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing 100872, China [3].

ABSTRACT
Two-dimensional crystals are emerging materials for nanoelectronics. Development of the field requires candidate systems with both a high carrier mobility and, in contrast to graphene, a sufficiently large electronic bandgap. Here we present a detailed theoretical investigation of the atomic and electronic structure of few-layer black phosphorus (BP) to predict its electrical and optical properties. This system has a direct bandgap, tunable from 1.51 eV for a monolayer to 0.59 eV for a five-layer sample. We predict that the mobilities are hole-dominated, rather high and highly anisotropic. The monolayer is exceptional in having an extremely high hole mobility (of order 10,000 cm(2) V(-1) s(-1)) and anomalous elastic properties which reverse the anisotropy. Light absorption spectra indicate linear dichroism between perpendicular in-plane directions, which allows optical determination of the crystalline orientation and optical activation of the anisotropic transport properties. These results make few-layer BP a promising candidate for future electronics.

No MeSH data available.