Distribution Of Electroluminescence Research Articles

A proposal of a procedure to estimate a standard line for contactless estimation of a solar cell voltage in a module using modulated light

AbstractIt is important to measure the operating voltage of a cell sealed in a photovoltaic module as well as well‐known faults such as abnormal hot spots observed by thermography or a dark part in electroluminescence distribution on the module for detecting a fault module. This paper proposes a method that radiating modulated light toward a cell and extracting the synchronized signal from the module output by phase detector can estimate the operating voltage quantitatively by using a standard line predicted by shading the module partially.

Impact of grain growth of silver reflective electrode by electron bombardment on external quantum efficiency of III-nitride micro-light-emitting diode arrays

The effect of electron-beam irradiation (EBI) on Ag reflector is investigated in order to improve the efficiency of flip-chip InGaN/GaN multiple-quantum-wells micro light-emitting diode (μ-LED) arrays. After EBI, small size grains are diffused and then become larger grain. Therefore, grain boundaries are reduced which originates both the crystal quality and the reflectance of Ag reflect to improve. Grain size of Ag reflector is increased with the increase in EBI time that is consistently observed by different kinds of material characterizations. 5 min EBI-based Ag reflector shows higher reflectance (~91%) at 450 nm than without EBI sample (~84%). Finally, without and with EBI on Ag reflector-based μ-LED arrays are fabricated. After EBI, there is no change in forward bias voltage except optical performances. At driving current, Ag reflector with EBI-based μ-LEDs has higher light-output-power, electroluminescence intensity and electroluminescence distribution over the chip area compared to without EBI-based μ-LEDs. Usually, increased light-extraction-efficiency causes the external-quantum-efficiency of the μ-LEDs to increase. These enhanced optoelectronic performances are consistently described by using microscopic and macroscopic characterizations.

Electroforming of Amorphous Silicon Nitride Heterojunction $pin$ Visible Light Emitter

The deposition parameters of doped hydrogenated nanocrystalline silicon grown by plasma-enhanced chemical vapor deposition were scanned to obtain highly conductive films. The optimized p+ and n+ nc-Si:H films were used as injecting layers in the fabrication of Si-rich hydrogenated amorphous silicon nitride (a-SiNx:H)-based heterojunction p+in+ diode. The as-grown diode was subjected to a Joule-heating-assisted forming process (FP) via the application of a high electric field. The modifications in the luminescent, electrical, and structural properties of the diode subsequent to the FP were investigated. Although the energy distribution of electroluminescence remains almost the same when compared with that of the fresh diode, its intensity is enhanced by at least 30 times with an orange-red emission easily perceived by the naked eye. Parallelly, the low field-current density drastically increases, presumably due to the Si-nanocrystallite formation within the a-SiNx:H layer. This formation, triggered by the neighboring nanocrystalline-doped layers, was confirmed by the X-ray diffraction measurements indicating the rise in the local temperature during FP.

Nonuniformity of carrier injection and the degradation of blue LEDs

The distribution of electroluminescence (EL) intensity over the area and in the course of time before and after the optical degradation of blue InGaN/GaN LEDs is studied. Current-voltage characteristics have been recorded. It is found that the initially bright luminescence near the region of metallization of the p-contact turns weak after the degradation of an LED. The time delay of ∼20–40 ns is observed in the distribution of EL intensity over the area of LEDs after their degradation. We suppose that a rise in the excess current after degradation is due to the density increasing of the InGaN/GaN interface states and the formation of an electrical dipole, which lowers the potential barriers in p-GaN and n-GaN layers. The corresponding increase of capacitance leads to a time delay in the spreading of the injection current and in the distribution of the emission brightness over the area. The lateral nonuniformity of the carrier injection into the quantum, well before and after optical degradation, is attributed to diffusion and electromigration of hydrogen, induced by mechanical stress. The metallization of the p-contact may be the source of mechanical stress.

LED flip‐chip assembly with electroplated AuSn alloy

InGaN based high brightness (HB)-LED chips have been fabricated and bonded to substrates that were coated with electroplated Au/Sn/Au solder. The assemblies yielded a forward voltage of 5.6 V and an optical output power of 42 mW when tested at 1,000 mA bias. The electroluminescence distribution was mapped with a CCD camera to determine the current spreading into the p-contact region. Computational fluid dynamics (CFD) was used to check the effect of non-uniform current spreading on the thermal resistance of the assemblies. We show that a good knowledge of the non-uniform heat generation is required to obtain accurate modelling results. The bond strength of the AuSn solder joints exceeded the norm, when shear tested according to MIL-STD-883E (method 2019.5). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)