Publications by authors named "Arman Rashidi"
Dirac and Weyl semimetals, such as cadmium arsenide (CdAs), have recently attracted attention for use in high-speed photodetectors that operate at longer infrared wavelengths, where conventional semiconductor-based photodetectors have a limited performance. In this Letter, we explore near-infrared (960 nm) photodetection in a CdAs/AlSb heterojunction. We show that CdAs/AlSb heterojunctions allow for an unbiased operation and demonstrate an enhanced responsivity and quantum efficiency compared to AlSb and CdAs reference devices.
View Article and Find Full Text PDFEpitaxial heterostructures with topological insulators enable novel quantum phases and practical device applications. Their topological electronic states are sensitive to the microscopic parameters, including structural inversion asymmetry (SIA), which is an inherent feature of many real heterostructures. Controlling SIA is challenging, because it requires the ability to tune the displacement field across the topological film.
View Article and Find Full Text PDFCadmium arsenide (CdAs) thin films feature a two-dimensional topological insulator (2D TI) phase for certain thicknesses, which theoretically hosts a set of counterpropagating helical edge states that are characteristic of a quantum spin Hall (QSH) insulator. In devices containing electrostatically defined junctions and for magnetic fields below a critical value, chiral edge modes of the quantum Hall effect can coexist with QSH-like edge modes. In this work, we use a quantum point contact (QPC) device to characterize edge modes in the 2D TI phase of CdAs and to understand how they can be controllably transmitted, which is important for use in future quantum interference devices.
View Article and Find Full Text PDFTwo-dimensional topological insulators (2D TIs) are a highly desired quantum phase but few materials have demonstrated clear signatures of a 2D TI state. It has been predicted that 2D TIs can be created from thin films of three-dimensional TIs by reducing the film thickness until the surface states hybridize. Here, we employ this technique to report the first observation of a 2D TI state in epitaxial thin films of cadmium arsenide, a prototype Dirac semimetal in bulk form.
View Article and Find Full Text PDFArticle Synopsis
- Multiphysics processes like recombination dynamics, carrier transport, and internal heating play key roles in causing thermal and efficiency droop in InGaN/GaN LEDs, but a clear method to differentiate these processes has been lacking.
- This study explores thermal and efficiency droop in single-quantum-well InGaN/GaN LEDs by separating factors such as radiative efficiency and carrier transport using a detailed rate equation framework and a temperature-sensitive pulsed-RF measurement technique.
- Findings reveal that high current densities lead to efficiency droop primarily due to strong non-radiative recombination and saturation of radiative rates, with thermal droop caused by carriers shifting from radiative to non-radiative processes at elevated temperatures
Article Synopsis
- - The study investigates the carrier dynamics and recombination coefficients in semipolar InGaN/GaN light-emitting diodes (LEDs) that emit at 440 nm and have a high internal quantum efficiency of 93%.
- - By analyzing the differential carrier lifetime across various current densities, the researchers differentiate between radiative and nonradiative recombination processes, enabling them to extract key recombination coefficients (A, B, and C).
- - Results reveal that semipolar LEDs demonstrate a significantly higher A and B coefficient compared to c-plane LEDs, with lower carrier density and Auger recombination coefficient, contributing to better performance and reduced efficiency droop.