KEYWORDS: Indium gallium nitride, Solar cells, Laser irradiation, Resistance, Temperature metrology, Laser applications, Wireless energy transfer, Sapphire, Retina, Power supplies
We tested the optical wireless power transmission (OWPT) using InGaN photovoltaic cells and lasers below 400 nm. As a result, 24.5% and 20.8% photoelectric conversion efficiencies were obtained at laser power densities of 16.5 mW/cm2 and 398 mW/cm2, respectively. The conversion efficiency decreased as incident laser power increased. On the other hand, the conversion efficiencies increased with increasing the temperature of the InGaN photovoltaic cells. We investigated the causes of these phenomena and found that lower resistance and improved crystal quality of InGaN cells significantly improve conversion efficiency further.
A nitride-based light-emitting structure composed of a GaN nanowire core and a GaInN/GaN multi-quantum shell (MQS) is promising for high performance optoelectronic devices. By growing high crystalline quality MQS on the nonpolar (m-plane) sidewall of the nanowires, an improvement of luminous efficiency is expected. In this work, we induced the sputtering growth of n++-GaN shell on the tunnel junction/p-GaN/MQS/nanowire structures. By performing sputtering by the optimized condition, we were able to demonstrate a device with an operating voltage of about 1.0 V lower than that of the sample without sputtering.
Suppressing the emission from (0001) plane region with low luminescence efficiency that exists on the top of nanowires (NWs) is necessary to realize highly efficient GaInN/GaN multi quantum shell (MQS) light-emitting diodes (LEDs). In this study, we attempted to improve the crystal growth by introducing electron blocking layers (EBLs) and to suppress the current leak in NW LEDs by using SiO2 insulating film on top of NWs. The EBL structure features different thicknesses at each crystalline plane to reduce the current injection into (0001) plane, suppress red emission with low luminescence efficiency, and improve the light output by 2.4 times. Given that the luminescence from (0001) plane region remains, further optimization of EBL growth conditions, such as V/III ratio and Al composition, is essential. In addition, the luminescence from (0001) plane region and the current leakage can be reduced by forming SiO2 insulating film on top of the NWs. Although even if an insulating film was formed on the top of NWs on which EBLs were grown, the SiO2 adhering to (1-101) plane resulted in a decrease in light output and destruction due to high resistance. The results indicate the possibility of realizing highly efficient GaInN/GaN MQS-NW LEDs by inserting EBL structures between MQS and p- GaN shell.
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