Due to low power consumption, tunable wavelength and long lifetime ultraviolet light‐emitting diodes (UV LEDs) have found many applications in different fields such as health care, water disinfection, agriculture. In this review, we report different problems that lead to low external quantum efficiency of UV LEDs. We also report various challenges in the growth process of the UV LEDs such as increase in the dislocation density, which affects the optoelectronic performance of the devices. We also report the analysis of the two modes of light polarization, i.e. transverse electric and transverse magnetic in UV LEDs. Moreover, we also summarize various state‐of‐the‐art reported external quantum efficiencies, light output power and peak emission wavelengths in the three UV wavelength regimes, i.e. UV‐A, UV‐B and UV‐C LEDs.

No abstract

No abstract

The optoelectronic properties of semiconducting aluminum gallium nitride (AlGaN)-based ultraviolet-B (UVB) light-emitting diodes (LEDs) are crucial for real-world medical applications such as cancer therapy and immunotherapy. However, the performance of AlGaN-based UVB LED devices is still poor due to the low hole injection efficiency. Therefore, we have numerically investigated the performance of AlGaN-based UVB LEDs for the suppression of efficiency droop as well as for the enhancement of hole injection in the multiquantum wells (MQWs). The influence of the undoped (ud)-AlGaN final quantum barrier (FQB), as well as the Mg-doped multiquantum barrier electron blocking layer (p-MQB EBL), on the efficiency droop has been focused on specifically. To evaluate the performance of the proposed device, we have compared its internal quantum efficiency (IQE), carrier concentration, energy band diagram, and radiative recombination rate with the conventional device structure. Furthermore, the influence of Al composition in the Al-graded p-AlGaN hole source layer (HSL) on the operating voltages of the proposed UVB LEDs was considered. The simulation results suggest that our proposed structure has a high peak efficiency and much lower efficiency droop as compared to the reference structure (conventional). Ultimately, the radiative recombination rate in the MQWs of the proposed UVB LED-N structure has increased up to ∼73%, which is attributed to the enhanced level of electron and hole concentrations by ∼64% and 13%, respectively, in the active region. Finally, a high efficiency droop of up to ∼42% in RLED has been successfully suppressed, to ∼7%, by using the optimized ud-AlGaN FQB and the p-MQB EBL, as well as introducing Al-graded p-AlGaN HSL in the proposed UVB LED-N structure.

No abstract

High piezoelectric field in green light-emitting diodes (LEDs) has been a challenge for direct measurement for a long time. In this work, we report the direct experimental measurement of the large piezoelectric field in green LEDs by using single-and double-quantum-well samples with the electroreflectance spectroscopy at room temperature. Comparison with the theoretical prediction indicates that there is an influence of defects in reducing the piezoelectric field in green LED samples.

To improve the internal quantum efficiency of green light-emitting diodes, we present the numerical design and analysis of bandgap-engineered W-shaped quantum well. The numerical results suggest significant improvement in the internal quantum efficiency of the proposed W-LED. The improvement is associated with significantly improved hole confinement due to the localization of indium in the active region, leading to improved radiative recombination rate. In addition, the proposed device shows reduced defect-assisted Shockley-Read-Hall (SRH) recombination rate as well as Auger recombination rate. Moreover, the efficiency rolloff in the proposed device is associated with increased built-in electromechanical field.

In this paper, a unique and more distinctive encryption algorithm is proposed. This is based on the complexity of highly nonlinear S box in Flesnelet domain. The nonlinear pattern is transformed further to enhance the confusion in the dummy data using Fresnelet technique. The security level of the encrypted image boosts using the algebra of Galois field in Fresnelet domain. At first level, the Fresnelet transform is used to propagate the given information with desired wavelength at specified distance. It decomposes given secret data into four complex subbands. These complex sub-bands are separated into two components of real subband data and imaginary subband data. At second level, the net subband data, produced at the first level, is deteriorated to non-linear diffused pattern using the unique S-box defined on the Galois field . In the diffusion process, the permuted image is substituted via dynamic algebraic S-box substitution. We prove through various analysis techniques that the proposed scheme enhances the cipher security level, extensively.