Polymorphism of CdTe in the Few‐Monolayer Limit

Abstract

Decreasing the thickness of semiconductors to the few monolayer limit often results in structural relaxation and the appearance of new properties. Herein, the bistability of 2ML thick CdTe, where the zinc blende structure of the bulk phase is metastable and the stable (ground) state is represented by an inverted structure with Cd atoms sandwiched by Te planes, is demonstrated. The thermodynamic stability of both phases is demonstrated by the absence of imaginary modes in the phonon dispersion spectra of both phases fully relaxed at 0 K. Both phases are direct‐gap semiconductors and the transformation from the zinc blende phase to the inverted phase is accompanied by a marked increase of the bandgap from 0.13 to 1.03 eV. In combination with the stable α‐CdTe phase, results demonstrate the polymorphism of ultrathin CdTe. A pronounced property contrast between the phases suggests the possible use of few‐monolayer CdTe for memory applications.

Bonding Heterogeneity Inducing Low Lattice Thermal Conductivity and High Thermoelectric Performance in 2D CdTe2

“…Other metastable 2D CdTe, CdTe 2 , and CdTe 3 are shown in Figure S3. Consistent with the investigation of Kolobov et al, the CdTe monolayer adopts a honeycomb prototype with the space group P 3̅ m 1 and lattice constants a = b = 4.67 Å. In CdTe, each Cd atom is coordinated by four Te atoms in CdTe with two distinct distances of 2.86 and 3.06 Å.…”

“…The 2D CdTe possesses a direct band gap of 1.82 eV with the valence band maximum (VBM) and conduction band minimum (CBM) located at Γ points. Our predicted band gap is higher than the previously reported value (1.03 eV), obtained using the PBEsol method . The highly dispersive CBM and relatively flat VBM in CdTe suggest a low electronic and high hole effective mass.…”

“…In 2020, Naseri et al built a planar 2D CdTe, with the use of the predicted CdS honeycomb structure . Afterward, Kolobov et al reported a two-monolayer-thick CdTe slab (cleaved from bulk CdTe) that has extremely low formation enthalpies and a direct band gap of 1.03 eV . However, the structure configuration, phase stability, and thermoelectric performance of diverse 2D CdTe still lack a full investigation.…”

Enhancement of Spin Pumping from CoFeB to Sb2Te3 Layers by Crystal Orientation Control

“…Moreover, surface sensitive topological states have been recently reported theoretically, where the Dirac cone appears at the Te‐terminated (001) surface, while the band structure becomes either metallic or insulating at side surfaces. [ 33 ] Therefore, even though some small crystal grains were observed in the amorphous film, the orientation of crystals is random and the atomic order of Sb 2 Te 3 at the interface is not uniform resulting in absence of the linewidth broadening in the amorphous film. In addition, Δ H of the crystalline Sb 2 Te 3 film is comparable with the amorphous film at thickness greater than 7 nm film, suggesting that the bulk effect becomes more dominant than the surface effect for the thicker films.…”

Recent Progress in Double-Layer Honeycomb Structure: A New Type of Two-Dimensional Material

“…Therefore, new configurations that can stabilize traditional semiconductors in their 2D limit are still required to be investigated. In 2018, Lucking et al theoretically propose a 2D structure named double-layer honeycomb (DLHC) [ 30 ], which is demonstrated to have lower formation energy than the truncated bulk and other 2D counterparts, such as in CdTe [ 31 , 32 ], AlSb [ 33 , 34 ], and InAs [ 35 ]. Later, several such kinds of 2D materials are successfully fabricated in experiments [ 34 , 36 , 37 , 38 ].…”