Transition from Schottky to Ohmic contacts in 2D Ge/GaAs heterostructures with high tunneling probability.

The metal-semiconductor (M-S) contact is usually an Ohmic contact or a Schottky contact, which greatly affects the electronic properties of devices, and it remains a huge challenge to realize a low-resistance Ohmic contact in a metal-semiconductor junction (MSJ). Herein, we systematically studied the band structures, electrostatic potential, charge transfer, Schottky barrier height of carriers, effective carrier masses, and tunneling probability of carriers of a germanene (Ge)/GaAs MSJ. The transition from the Schottky to the Ohmic contact can be caused by applying certain biaxial strains or electric fields, which weakens the Fermi level pinning (FLP) effect and reduces contact resistance. Meanwhile, the electron injection efficiency of Ge/(GaAs)As MSJ (PTB > 27%) is far superior to that of other two-dimensional (2D) vdW MSJs. This work indicates that Ge/GaAs heterostructures are the most compatible for applying high-effective 2D electronic nanodevices under controllable conditions.

Recycled Bifunctional Heterostructure Material: g-GaN/SnS for Photocatalytic Decomposition of Water and Efficient Detection of NO2.

Recently, the energy crisis and environmental pollution problems have become increasingly severe. There is an urgent need to develop a class of multifunctional materials that can both produce clean energy and detect harmful gases. Herein, we propose a g-GaN/SnS heterostructure and explored its dual-optimal performance in photocatalytic hydrogen production and gas detection. Our results demonstrated that the g-GaN/SnS heterostructure has a suitable type II band alignment and excellent absorption in the visible range, which both indicate its potential application in photocatalysis. Furthermore, when the g-GaN/SnS heterostructure acted as a gas detection material, it was consistently susceptible to NO2 gas molecules, according to charge transfer. Additionally, it has a very suitable material recovery time (∼0.5 h) when used for NO2 detection, illustrating the recyclability of the material. Interestingly, the applied electric field of -0.4 V/Šcan greatly increase the absorption coefficient in the visible range to 150% of the original. Also, the applied electric field of 0.6 V/Šcan substantially enhance the gas detection sensitivity by 27% compared to the case without the electric field. Thus, the g-GaN/SnS heterostructure we proposed not only has the advantage of being bifunctional but also has the potential to be recycled.

GaN/MgI2 van der Waals heterostructure: a two-factor tunable photocatalyst for hydrogen evolution.

With the increasing environmental pollution and energy crisis, it is significant to develop environmentally friendly and adjustable photocatalysts for water splitting. Here we explored the optoelectronic properties of several H-GaN/MgI2 vdW heterostructures by regulating different polarization surfaces and numbers of GaN layers. Our results demonstrate that all structures, except 2L-Ga-GaN/MgI2, exhibit excellent physical stability. Moreover, the band structures and band edge positions demonstrate that only the heterostructure of 3L-Ga-GaN/MgI2 with both suitable band alignment (type-II) and an acceptable band gap (∼1.92 eV) is most satisfactory for water splitting. Additionally, the absorption coefficient of the 3L-Ga-GaN/MgI2 heterostructure can reach over ∼105 cm-1, which has further confirmed its excellent advantage in photocatalysis. Finally, in the case of 6% external strain for the 3L-Ga-GaN/MgI2 heterostructure, a rollover in band alignment (from type-II to type-I) is exhibited. These promising features of the GaN/MgI2 vdW heterostructure give a new paradigm for developing novel efficient and adjustable photocatalytic water-splitting materials.

How the Spacer Influences the Stability of 2D Perovskites?

Two-dimensional lead halide perovskites (2D HPs) represent as an emerging class of materials given their tunable optoelectronic properties and long-term stability in perovskite solar cells. However, the ever-growing field of optoelectronic devices using 2D HPs requires fundamental understanding of the influence of the spacer on the physiochemical properties and stability of perovskites as well as establish which cation properties are closely related to suppress the halogen ion mobility. This study focuses on investigating the influence of organic spacers with intrinsic properties (e.g., rigidity and flexibility, special groups) and variations of material dimensions on the stability of halogen ions and inorganic frameworks in 2D HPs. It is found that the perovskite structure composed of rigidity molecules owns better stability of halogen ion and inorganic framework than that of flexible molecules. The stability of ions exhibits a negative correlation with the dimensions of perovskite. More importantly, a simple descriptor for measuring the stability of halogen ions in 2D HPs is constructed. By causal discovery algorithms with more physical and chemical significance, the Kappa shape index, number of rotatable bonds, and aromatic carbocycles in organic spacers are identified as causal and important features for the stability of halogen ions in 2D HPs.

Impact of residual gas on the optoelectronic properties of Cs-sensitized In0.53Ga0.47As (001) surface.

Near-infrared InxGa1-xAs photocathode with better optoelectronic properties is a good candidate for low-light-level (LLL) night-vision system. However, the residual gases in the ultra-high vacuum (UHV) system inevitably affects the stability and photo-emission performance of LLL photoelectric devices such as their quantum efficiency and life-time. In this study, the first-principles calculations were used to investigate the adsorption effect of five different residual gas species, including H2, CH4, CO, H2O and CO2 on Cs-sensitized In0.53Ga0.47As (001) ß2 (2 × 4) surface. The study results indicate that CO2 gas molecule is the most easily attached to the Cs-sensitized surface. The adsorption of residual gases leads to the formation of a new dipole pointing from inner Cs atoms to gas molecules. It makes the charge center of the adsorbates escape from the surface, which weakens the interaction between the inner Cs atoms and the clean surface. This results in the increase of the surface work function and degradation of the performance of photoelectric devices. Also, the adsorption of residual gas molecules influences the absorption and reflection coefficients of Cs-sensitized In0.53Ga0.47As (001) ß2 (2 × 4) surface.