GaN nanocolumns exhibiting high light-extraction property provide a platform for high-performance nano-devices. To improve the performance of nanocolumn LEDs, uniform arrays of InGaN-based multi quantum well (MQW) nanocolumns were fabricated. We report on red emitting nanocolumn LEDs with InGaN MQW grown on GaN templates by radio frequency plasma assisted molecular beam epitaxy (RF-MBE), for the first time. The electroluminescence peak wavelength and the full-width at half maximum at a drive current of 5 mA were 633 nm and 185 meV, respectively for the LEDs. It demonstrated a blue-shift of 5 nm for the 20 mA, indicating negligible polarization and band filling effects.
We fabricated ordered GaN nanocolumns (NCs) with InGaN/GaN multiple quantum wells (MQWs) that emitted light at wavelengths of 590–600 nm by rf-plasma assisted molecular beam epitaxy. The NCs exhibited sharp emission with a full width at half maximum of 44–45 nm, and the internal quantum efficiency (IQE) was evaluated to be 17 to 22% by investigating the temperature dependence of the photoluminescence of the NCs. Although the accuracy of the IQE value is still debatable, we claim that the NCs exhibited an IQE that compared favorably with that of green-emitting film InGaN MQWs grown by metal–organic chemical vapor deposition.
It is evident that radar sensing is robust technology compared to camera or LiDAR in the case of autonomous vehicles. Since, they are capable of working even under harsh weather conditions like thick fog, glaring sun, etc. The 77-81GHz frequency band for short range radar provides a global framework for automotive radar by preventing collisions, reducing traffic accidents and thus improvingvehicular safety. The proposed antenna resonates at 79GHz. Below-10dB, return loss characteristic greater than -35dB is obtained in the band of 77.5GHz to 80.4GHz (i.e., impedance bandwidth of 2.86GHz) and gain of above 8dB is achieved. Rectangular vias and complementary concentric square loops of the metamaterial structure are introduced to suppress the surface waves and to achieve the desired frequency of resonance. The feed line and the metamaterial structure are positionedaccordinglyto provide a better impedance matching. VSWR obtained is 1.04 and the antenna is linearly polarized and has a low profile. The total dimension of the antenna is 1.96×2.26×0.127mm3. The antenna structure can be used in an array for automotive radar applications.
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