Oxygen-vacancy-induced magnetism in anti-perovskite topological Dirac semimetal Ba3SnO

Bi2Te2Se and Sb2Te3 heterostructure based photodetectors with high responsivity and broadband photoresponse: experimental and theoretical analysis

Topological insulators have emerged as one of the most promising candidates for the fabrication of novel electronic and optoelectronic devices due to the unique properties of nontrivial Dirac cones on the surface and a narrow bandgap in the bulk. In this work, the Sb2Te3 and Bi2Te2Se materials, and their heterostructure are fabricated by metal-organic chemical vapour deposition and evaporation techniques. Photodetection of these materials and their heterostructure shows that they detect light in a broadband range of 600 to 1100 nm with maximum photoresponse of Sb2Te3, Bi2Te2Se and Sb2Te3/Bi2Te2Se at 1100, 1000, and 1000 nm, respectively. The maximum responsivity values of Sb2Te3, Bi2Te2Se, and their heterostructure are 183, 341.8, and 245.9 A W-1 at 1000 nm, respectively. A computational study has also been done using density functional theory (DFT). Using the first-principles methods based on DFT, we have systematically investigated these topological insulators and their heterostructure's electronic and optical properties. The band structures of Sb2Te3 and Bi2Te2Se thin films (3 QL) and their heterostructure are calculated. The bandgaps of Sb2Te3 and Bi2Te2Se are 26.4 and 23 meV, respectively, while the Sb2Te3/Bi2Te2Se heterostructure shows metallic behaviour. For the optical properties, the dielectric function's real and imaginary parts are calculated using DFT and random phase approximation (RPA). It is observed that these topological materials and their heterostructure are light absorbers in a broadband range, with maximum absorption at 1.90, 2.40, and 3.21 eV.

Exploring the direction-dependency of conductive filament formation and oxygen vacancy migration behaviors in HfO2-based RRAM

Oxygen vacancy (V_O) defects play an essential role in governing the conductivity of semiconductor materials. The direction-dependency of oxygen vacancy conductive filament (CF) formation and V_O migration behaviors in HfO₂-based resistive random access memory (RRAM) were systematically investigated through first-principles calculations. The energetic and electronic structural analyses indicate that the continuous distribution of 3-fold oxygen vacancy (V_O3) or 4-fold oxygen vacancy (V_O4) is more favorable for the CF formation along [010] and [001] directions, and a continuous distribution between V_O3 and V_O4 in the m-HfO₂ system can also combine to promote the formation of CFs along a particular direction. Furthermore, the high annealing temperature and low oxygen partial pressure (P_O2) could effectively reduce the V_O formation energy and promote the formation of CFs, resulting in a lower applied voltage of the devices. Our results indicate that q = 0 and q = +2 are the most probable charge states for V_O3 and V_O4 in m-HfO₂. Subsequently, it is found that the low activation energy of V_O originates from the +2q charged V_O3 or V_O4 migrating in the CFs along a particular crystallographic [001] direction. The diffusion coefficient (D) of the oxygen atom along the [001] direction is much higher than that of all the other possible pathways considered, due to the lower energy barrier. This demonstrates that the growth of CFs is potentially direction-dependent, and that a lower forming voltage and lower SET voltage are required when the CFs are grown along a particular direction in RRAM devices. The present work would help to provide a fundamental guide and new understanding for the development and application of HfO₂-based RRAM.