Comprehensive Study on Piezo-Phototronic Effect: Way Forward for Ferrite Based Solar Cells

The wurtzite structured materials possess the inner-crystal piezopotential which comprehensively tune or control the charge carrier generation, separation, transportation, and recombination in optoelectronic devices. The piezo-phototronic effect provides a new working principle to the current traditional devices. Its effect on solar cells progresses made by the eminent scientists, and researchers in the field of piezo-phototronic modulated solar cells such as semiconductor-based, perovskite-based, multiple quantum-well (MQW) based and core/shell based. It has been described that the piezo-phototronic effect has improved the power conversion efficiency (PCE) of the solar cells, and the effect of temperature on the piezo-phototronic devices. Ferrite-based materials have emerged as a viable candidate for use in solar cells. As a result of this research, ferrite-based nanomaterials can now be used in solar cell applications, as well as the piezophototronic effect on these materials can be investigated. The piezo-phototronic effect is a novel subject that offers a new platform for material science and electronics to investigate.

The Atomic Rearrangement of GaN-Based Multiple Quantum Wells in H2/NH3 Mixed Gas for Improving Structural and Optical Properties

In this work, three GaN-based multiple quantum well (MQW) samples are grown to investigate the growth techniques of high-quality MQWs at low temperature (750 °C). Instead of conventional temperature ramp-up process, H2/NH3 gas mixture was introduced during the interruption after the growth of InGaN well layers. The influence of hydrogen flux was investigated. The cross-sectional images of MQW via transmission electron microscope show that a significant atomic rearrangement process happens during the hydrogen treatment. Both sharp interfaces of MQW and homogeneous indium distribution are achieved when a proper proportion of hydrogen was used. Moreover, the luminescence efficiency is improved strongly due to suppressed non-radiative recombination process and a better homogeneity of MQWs. Such kind of atomic rearrangement process is mainly caused by the larger diffusion rate of gallium and indium adatoms in H2/NH3 mixed gas, which leads to a lower potential barrier energy to achieve thermodynamic steady state. However, when excessive hydrogen flux is introduced, the MQW will be partly damaged, and the luminescence performance will deteriorate.

Highly efficient top-down processed blue InGaN nanoscale light-emitting diodes

Demands for high-performance displays with high pixel density and picture quality are ever increasing. Indium gallium nitride (InGaN)-based micro-LEDs (μLEDs) are suitable for meeting such demands owing to their high efficiency, brightness, and stability. However, the poor yield of the pick-and-place technique, defect repair, and visibility of edge lines between modules limit the applications of μLEDs. Furthermore, the external quantum efficiency (EQE) decreases (<10%) when μLED size is reduced to less than 10 μm for high pixel densities, thereby limiting the luminance. Here, we demonstrate a top-down-processed blue InGaN/GaN multiple-quantum well (MQW) nanorod-LED (nLED) can be made highly efficient as well as become an enabling technology for reducing manufacturing cost of large-screen displays. A pixel array comprising of horizontally-aligned nLEDs between pixel electrodes can be cost-effectively fabricated by applying the dielectrophoretic force to the inkjet-printed nLEDs dispersed in ink solution. To overcome size-dependent EQE reduction problem, we studied the interaction between the GaN surface and the surface passivation layer via various analyses and found that minimizing the point defects created during the passivation process is crucial to manufacturing high-performance nanoscale LEDs. Notably, the sol–gel method is advantageous for the passivation because SiO2 nanoparticles are adsorbed on the GaN surface, thereby minimizing its atomic interactions. The fabricated nLEDs exhibited an EQE of 20.2±0.6%, the highest EQE value ever reported for the LED in the nanoscale. This work opens the way for manufacturing self-emissive nLED displays that can fully meet the industry requirements of high efficiency and brightness and low-power consumption, contributing to energy saving, carbon neutrality and mitigating climate crisis.