Pressure-Induced Phase Transitions in Germanium Telluride: Raman Signatures of Anharmonicity and Oxidation

Abstract

Pressure induced phase transitions in GeTe, a prototype phase change material have been studied to date with diffraction which is not sensitive to anharmonicity induced dynamical effects. GeTe is also prone to surface oxidation which may compromise surface sensitive measurements. These factors could be responsible for the lack of clarity about the phases and transitions intervening in the phase diagram of GeTe. We have used high pressure Raman scattering and ab initio pseudopotential density functional calculations to unambiguously establish the high pressure phase diagram and identify three phases up to 57 GPa, a low-pressure rhombohedral phase, an intermediate pressure cubic phase and a high pressure orthorhombic phase. We detect substantial broadening and softening of Raman modes at low pressure and identify the transition regions and possible intermediate phases.

GW study of pressure-induced topological insulator transition in group-IV tellurides

“…The rhombohedral distortion consists in a relative displacement of the two sublattices along the pseudocubic [111] direction, accompanied with an elongation of the cell along the same direction. High pressure Raman-scattering measurements show that the off-centering disappears at ∼3 GPa, and the complete transition to cubic occurs for P < 6 GPa [52]. Since our constrained calculations for the cubic phase predict the electronic topological transition to occur at a lower pressure than the structural one, we expect GeTe to be a crystalline topological insulator for pressures higher than the structural transition pressure of ∼6 GPa.…”

Pressure‐Dependent Behavior of Defect‐Modulated Band Structure in Boron Arsenide

“…Representative examples are superconductivity in superhydrite, [ 16 ] semiconductor‐to‐metal transition in transition metal dichalcogenides (TMDs), [ 17 ] and phase transition of GaTe. [ 18 ] One particular example is the strain‐induced thermal conductivity enhancement by ≈7X observed in MoS 2 at 15 GPa. [ 19 ] Hence, investigating the strain/pressure‐dependent electronic band structure and impurities levels of BAs could enable new functionalities for electronic devices.…”

Delayed Charge Recombination by Open‐Shell Organics: Its Application in Achieving Superb Photodetectors with Broadband (400–1160 nm) Ultrahigh Sensitivity and Stability

“…[ 1 ] Advances in this area following the emergence of atomically thin 2D materials, such as graphene, MoS 2 and other types of transition‐metal dichalcogenides (TMDs), have offered promising routes to enhance functionality in photodetection. [ 2–11 ] This functionality mainly lies in their unique electronic and optical properties arising from the monolayer van der Waals heterostructure. [ 2–11 ] Among the various 2D materials that have been employed in ultrathin optoelectronic devices, MoS 2 has been highlighted because of extremely high stability, a direct bandgap, [ 9,12 ] reliable scalable synthesis, [ 10 ] excellent optoelectronic performances [ 9,12 ] and capability for heterogeneous integration.…”

“…[ 2–11 ] This functionality mainly lies in their unique electronic and optical properties arising from the monolayer van der Waals heterostructure. [ 2–11 ] Among the various 2D materials that have been employed in ultrathin optoelectronic devices, MoS 2 has been highlighted because of extremely high stability, a direct bandgap, [ 9,12 ] reliable scalable synthesis, [ 10 ] excellent optoelectronic performances [ 9,12 ] and capability for heterogeneous integration. [ 13–15 ] For example, MoS 2 ‐based PDs derived from single‐ and/or multilayer MoS 2 have been reported to respond to ultraviolet (UV) and visible light illumination, rendering photoresponsivities up to 880 A W −1 (monolayer) 7 and ≈0.6 A W −1 (few layers), [ 12 ] despite a relatively small bandgap (1.2 eV for MoS 2 ).…”