Interfacial Doping Effects in Fluoropolymer-Tungsten Diselenide Composites Providing High-Performance P-Type Transistors

In this study, we investigated the p-doping effects of a fluoropolymer, Cytop, on tungsten diselenides (WSe2). The hole current of the Cytop–WSe2 field-effect transistor (FET) was boosted by the C–F bonds of Cytop having a strong dipole moment, enabling increased hole accumulation. Analysis of the observed p-doping effects using atomic force microscopy (AFM) and Raman spectroscopy shed light on the doping mechanism. Moreover, Cytop reduces the electrical instability by preventing the adsorption of ambient molecules on the WSe2 surface. Annealing Cytop deposited on WSe2 eliminated the possible impurities associated with adsorbates (i.e., moisture and oxygen) that act as traps on the surface of WSe2. After thermal annealing, the Cytop–WSe2 FET afforded higher p-type conductivity and reduced hysteresis. The combination of the Cytop–WSe2 FET with annealing provides a promising method for obtaining high-performance WSe2 p-type transistors.

Characteristics of Vertical Carbon Nanotube Field-Effect Transistors on p-GaAs

A semiclassical method is used to simulate the characteristics of vertical carbon nanotube fieldeffect transistors on p-GaAs. The calculation results show unique transfer characteristics that depend on the sign of the drain voltage. The transistors exhibit p-type characteristics and ambipolar characteristics for a positive drain voltage and a negative drain voltage, respectively. The p-type characteristics do not change with the GaAs bandgap and doping level, because the hole current from the single-walled carbon nanotube (SWCNT) and drain side dominates the whole current. In contrast, the ambipolar characteristics are greatly influenced by the GaAs bandgap and doping level. Only the electron current in the ambipolar characteristics increases as the GaAs bandgap decreases. Increasing the p-type doping of GaAs increases the p-branch current and decreases the electron current (n-branch) of the ambipolar characteristics. The effects of the SWCNT bandgap and doping level are different from those of GaAs, and the impact of SWCNT on the p-type characteristics is much greater than the impact on the ambipolar characteristics. The p-type current increases as the SWCNT bandgap decreases.

Controlling Band Alignment at the Back Interface of Cadmium Telluride Solar Cells using ZnTe and Te Buffer Layers

ABSTRACTFormation of a low barrier back contact plays a critical role in improving the photoconversion efficiency of the CdTe solar cells. Incorporating a buffer layer to minimize the band bending at the back of the CdTe device can significantly lower the barrier for the hole current, improving open circuit voltage (VOC) and the fill factor. Over the past years, researchers have incorporated the both ZnTe and Te as buffer layers to improve CdTe device performance. Here we compare device performance using these two materials as buffer layers at the back of CdTe devices. We show that using Te in contact to CdTe results in higher performance than using ZnTe in contact to the CdTe. Low temperature current density-voltage measurements show that Te results is a lower barrier with CdTe than ZnTe, indicating that Te has better band alignment, resulting in less downward bending in the CdTe at the back interface, than ZnTe does.