AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency. The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-Al x Ga 1−x N has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-Al x Ga 1−x N, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.
The anomalous hysteresis in a perovskite solar cell induced by an asymmetric field is confirmed by a capacitancevoltage measurement. By applying several cycles of alternating reverse and forward scans, this hysteresis phenomenon is obviously alleviated, resulting in a hysteresis-less state in the perovskite solar cell. Meanwhile, the open-circuit voltage and power conversion efficiency of the perovskite solar cell are enhanced by 55.74% and 61.30%, respectively, while the current density and fill factor keep almost invariable. The operation of alleviating hysteresis is essential for further research and is likely to bring in performance gains.
Self-powered ultraviolet (UV) photodetectors have great
application
prospects in the fields of UV astronomy, environmental monitoring,
and space communication. In particular, the emerging photoelectrochemical
photodetectors (PEC PDs) without external bias, high sensitivity,
and environmental sensitivity have attracted extensive attention.
Herein, self-powered PEC PDs were designed and constructed by using
highly ordered GaN nanorod arrays (NRAs) as photoelectrodes. Without
external bias, PEC PDs with NRA structures exhibit a high peak responsivity
of 6.04 mA/W and a detectivity of 5.14 × 1010 Jones,
which are 12 and 5.1 times higher, respectively, than those of the
planar device. The large solid–liquid interface of the nanorod
structure will lead to an improved built-in electrical field to promote
carrier collection and rapid directional transmission, which can enhance
the generation and separation of photogenerated carriers. Moreover,
an optimized nanoarray will increase the UV detection effect significantly,
which provides instruction for the design and fabrication of high-performance
self-powered PEC PDs in the future.
We investigate the performances of the near-ultraviolet (about 350 nm-360 nm) light-emitting diodes (LEDs) each with specifically designed irregular sawtooth electron blocking layer (EBL) by using the APSYS simulation program. The internal quantum efficiencies (IQEs), light output powers, carrier concentrations in the quantum wells, energy-band diagrams, and electrostatic fields are analyzed carefully. The results indicate that the LEDs with composition-graded p-Al x Ga 1−x N irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs. The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface, which results in less electron leakage and better hole injection efficiency, thus reducing efficiency droop and enhancing the radiative recombination rate.
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