Mixed-Dimensional van der Waals Heterostructure (2D ReS2/0D MoS2 Quantum Dots)-Based Broad Spectral Range with Ultrahigh-Responsive Photodetector.

The remarkable properties of two-dimensional (2D) materials have led to significant advancements in photodetection and optoelectronics research. Currently, there are many successful methods that are employed to improve the responsivity of photodetectors, but the limited spectral range of the device remains a limitation. This work demonstrates the development of a mixed-dimensional (2D/0D) hybrid photodetector device fabricated using chemical vapor deposition (CVD)-grown monolayer ReS2 and solution-processed MoS2 quantum dots (QDs). The mixed dimensionality of 2D (ReS2) and zero-dimensional (0D) MoS2 QDs assist in improving the spectral range of the device [ultraviolet (360 nm) to near-infrared (780 nm)]. Further, due to the work function difference between ReS2 and MoS2 QDs, the built-in electric field across the mixed-dimensional interface promotes effective charge separation and migration, resulting in improved responsivities of the device. The calculated responsivities of the fabricated photodetector are 5.4 × 102, 3.3 × 102, and 2.6 × 102 A/W when subjected to visible, UV, and NIR light illumination, which is remarkable when compared to the existing reports on broadband photodetection. The mixed-dimensionality heterostructure coupled with contact engineering paves the way for highly responsive broadband photodetectors for potential applications in security, healthcare, etc.

Investigation of the electronic transport in GaN nanowires containing GaN/AlN quantum discs.

We report the investigation of electronic transport in GaN nanowires containing GaN/AlN quantum discs (QDiscs). The nanowires were grown by plasma-assisted molecular beam epitaxy and contacted by electron-beam lithography. Three nanowire samples containing QDiscs are analyzed and compared to a reference binary n-i-n GaN nanowire sample. The current-voltage measurements on single nanowires show that if the QDiscs are covered with a lateral GaN shell, the current mainly flows through the shell close to the lateral surface and the wire conductivity is extremely sensitive to the environmental conditions. On the contrary, if no GaN shell is present, the current flows through the QDisc region and a reproducible negative differential resistance related to electron tunneling through the QDiscs can be observed for temperatures up to 250 K. The demonstration of the resonant tunneling in GaN/AlN superlattices is of major importance for the development of nitride-based far-infrared quantum cascade lasers operating at high temperature.

Visible-blind photodetector based on p-i-n junction GaN nanowire ensembles.

We report the synthesis, fabrication and extensive characterization of a visible-blind photodetector based on p-i-n junction GaN nanowire ensembles. The nanowires were grown by plasma-assisted molecular beam epitaxy on an n-doped Si(111) substrate, encapsulated into a spin-on-glass and processed using dry etching and metallization techniques. The detector presents a high peak responsivity of 0.47 A W(-1) at - 1 V. The spectral response of the detector is restricted to the UV range with a UV-to-visible rejection ratio of 2 x 10(2). The dependence on the incident power and the operation speed of the photodetector are discussed.

High degree of polarization of the near-band-edge photoluminescence in ZnO nanowires.

We investigated the polarization dependence of the near-band-edge photoluminescence in ZnO strain-free nanowires grown by vapor phase technique. The emission is polarized perpendicular to the nanowire axis with a large polarization ratio (as high as 0.84 at 4.2 K and 0.63 at 300 K). The observed polarization ratio is explained in terms of selection rules for excitonic transitions derived from the k·p theory for ZnO. The temperature dependence of the polarization ratio evidences a gradual activation of the XC excitonic transition.PACS: 78.55.Cr, 77.22.Ej, 81.07.Gf.