A novel broken-gap chemical-bonded SiC/Ti2CO2 heterojunction with band to band tunneling: first-principles investigation.

A broken-gap heterojunction is a bright approach for designing tunneling field-effect transistors (TFETs) due to its distinct quantum tunneling mechanisms. In this study, we investigate the electronic structure and transport characteristics of a SiC/Ti2CO2 heterojunction, as well as the impacts of electric field and strain on the electronic properties via density functional theory. We determine that the interfacial atoms of the heterojunction are covalently bonded, forming a type-III heterojunction with a broken-gap. There exists band-to-band tunneling (BTBT) from the valence band (VB) of SiC to the conduction band (CB) of Ti2CO2. The creation of the heterojunction also enhances the carrier mobility arising from the large elastic modulus and the decrease of deformation potential. The current-voltage (I-V) characteristics of the device demonstrate a pronounced negative differential resistance (NDR) effect, along with a current that is about ten times greater than that of the vdW type-III heterojunction. Moreover, the tunneling window of SiC/Ti2CO2 is only slightly altered when subjected to an external electric field and vertical strain, demonstrating the remarkable stability of its type-III band alignments. Our results indicate that the SiC/Ti2CO2 heterojunction is useful to construct high-performance TFETs, and also introduces new ideas to design TFETs by using type-III covalent-bond heterojunctions.

InN/XS2 (X = Zr, Hf) vdW heterojunctions: promising Z-scheme systems with high hydrogen evolution activity for photocatalytic water splitting.

Z-scheme van der Waals heterojunctions are very attractive photocatalysts attributed to their excellent reduction and oxidation abilities. In this paper, we designed InN/XS2 (X = Zr, Hf) heterojunctions and explored their electronic structure properties, photocatalytic performance, and light absorption systematically using first-principles calculations. We found that the valence-band maximum (VBM) and conduction-band minimum (CBM) of the InN/XS2 (X = Zr, Hf) heterojunctions are contributed by InN and XS2, respectively. Photo-generated carriers transferring along the Z-path can accelerate the recombination of interlayer electron-hole pairs. Therefore, the photogenerated electrons in the CBM of the InN layer can be maintained making the hydrogen evolution reaction occur continuously, while photogenerated holes in the VBM of the Ti2CO2 layer make the oxygen evolution reaction occur continuously. The band edge positions of heterojunctions can straddle the required water redox potentials, while pristine InN and XS2 (X = Zr, Hf) can only be used for photocatalytic hydrogen evolution or oxygen evolution, respectively. Furthermore, the HER barriers can be tuned by transition metal doping. With Cr doping, the hydrogen evolution reaction (HER) barriers decrease to -0.12 for InN/ZrS2 and -0.05 eV for InN/HfS2, very close to the optimal value (0 eV). In addition, the optical absorption coefficient is as high as 105 cm-1 in the visible and ultraviolet regions. Therefore, the InN/XS2 (X = Zr, Hf) heterojunctions are expected to be excellent photocatalysts for water splitting.