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Joint communications and sensing (JCAS) is envisioned as a key feature in future wireless communications networks. In massive MIMO-JCAS systems, the very large number of antennas causes excessively high computational complexity in beamforming designs. In this work, we investigate a low-complexity massive multiple-input-multiple-output (MIMO)-JCAS system employing the maximum-ratio transmission (MRT) scheme for both communications and sensing. We first derive closed-form expressions for the achievable communications rate and Cram´er–Rao bound (CRB) as functions of the large-scale fading channel coefficients. Then, we develop a power allocation strategy based on successive convex approximation to maximize the communications sum rate while guaranteeing the CRB constraint and transmit power budget. Our analysis shows that the introduction of sensing functionality increases the beamforming uncertainty and inter-user interference on the communications side. However, these factors can be mitigated by deploying a very large number of antennas. The numerical results verify our findings and demonstrate the power allocation efficiency. 

Abstract Graphene-driving strain-pre-store engineering enables the epitaxy of strain-free AlN film with low dislocation density for DUV-LED and the unique mechanism of strain-relaxation in QvdW epitaxy was demystified. 

Although AlGaN-based deep ultraviolet (UV) light-emitting diodes (LEDs) have been studied extensively, their quantum efficiency and optical output power still remain extremely low compared to the InGaN-based visible color LEDs. Electron leakage has been identified as one of the most possible reasons for the low internal quantum efficiency (IQE) in AlGaN based UV LEDs. The integration of a p-doped AlGaN electron blocking layer (EBL) or/and increasing the conduction band barrier heights with prompt utilization of higher Al composition quantum barriers (QBs) in the LED could mitigate the electron leakage problem to an extent, but not completely. In this context, we introduce a promising approach to alleviate the electron overflow without using EBL by utilizing graded concave QBs instead of conventional QBs in AlGaN UV LEDs. Overall, the carrier transportation, confinement capability and radiative recombination are significantly improved. As a result, the IQE, and output power of the proposed concave QB LED were enhanced by ~25.4% and ~25.6% compared to the conventional LED for emission at ~254 nm, under 60 mA injection current. 

In this paper, we report on the enhanced light extraction efficiency (LEE) of AlInN nanowire ultraviolet light-emitting diodes (LEDs) at an emission wavelength of 283 nm using the surface passivation approach and hexagonal photonic crystal structures. Several dielectric materials including SiO 2 , Si 3 N 4 , HfO 2 , AlN, and BN, have been investigated as the surface passivation layer for the AlInN nanowire LEDs. The LEDs using these dielectric materials show significantly improved LEE compared to that of the unpassivated ultraviolet nanowire LEDs. With a 35nm Si 3 N 4 as surface passivation, the AlInN LED could achieve a LEE of ~ 42.6%, while the unpassivated LED could only have an average LEE of ~ 25.2%. Moreover, the LEE of the AlInN nanowire LEDs could be further increased using hexagonal photonic crystal structures. The periodically arranged nanowire LED arrays could reach up to 63.4% which is almost two times higher compared to that of the random nanowire LEDs. Additionally, the AlInN nanowire ultraviolet LEDs exhibit highly transverse-magnetic polarized emission. 

We report on the demonstration of electron blocking layer free AlInN nanowire light-emitting diodes (LEDs) operating in the 280–365 nm wavelength region. The molecular beam epitaxial grown AlInN nanowires have a relatively high internal quantum efficiency of > 52%. Moreover, we show that the light extraction efficiency of the nanowires could reach ~ 63% for hexagonal photonic crystal nanowire structures which is significantly higher compared to that of the random nanowire arrays. This study provides significant insights into the design and fabrication of a new type of high-performance AlInN nanowire ultraviolet light-emitters.