Multi‐color monolithic III‐nitride light‐emitting diodes: Factors controlling emission spectra and efficiency

et al. 2017

Materials

External quantum efficiency of industrial-grade green InGaN light-emitting diodes (LEDs) has been measured in a wide range of operating currents at various temperatures from 13 K to 300 K. Unlike blue LEDs, the efficiency as a function of current is found to have a multi-peak character, which could not be fitted by a simple ABC-model. This observation correlated with splitting of LED emission spectra into two peaks at certain currents. The characterization data are interpreted in terms of non-uniformity of the LED active region, which is tentatively attributed to extended defects like V-pits. We suggest a new approach to evaluation of temperature-dependent light extraction and internal quantum efficiencies taking into account the active region non-uniformity. As a result, the temperature dependence of light extraction and internal quantum efficiencies have been evaluated in the temperature range mentioned above and compared with those of blue LEDs.

f k is the fraction of photons emitted by the k -th QW in the total LED emission spectrum and

is IQE of the k -th well; summation in Equation (1) is performed over all N QWs.…”

Section: Modelingmentioning

confidence: 99%

Efficiency of True-Green Light Emitting Diodes: Non-Uniformity and Temperature Effects

Titkov

Karpov²,

et al. 2017

Materials

“…This effect leads to change of color coordinates of the emission in a wide enough range. Different spectral behavior from the first chip can be explained by its high sensitivity to the GaN barrier thickness [18]. Figure 6.…”

Section: Resultsmentioning

confidence: 99%

“…The first approach is similar to phosphor covered LEDs and the spectrum is controlled by number of passive QWs in active region. In addition, since the passive QWs are designed to operate on the green gap spectral range they being less efficient than phosphor for that range and their sensitivity to active QW emission wavelength is a disadvantage [18]. The best CRI for such devices reported is 41 [16].…”

Section: Introductionmentioning

confidence: 99%

Di-Chromatic InGaN Based Color Tuneable Monolithic LED with High Color Rendering Index

Titkov²,

Sakharov

et al. 2018

Applied Sciences

Abstract:We demonstrate a phosphor free, dichromatic GaN-based monolithic white LED with vertically stacked green and blue emitting multiple quantum wells. The optimal thickness of GaN barrier layer between green and blue quantum wells used is 8 nm. This device can be tuned over a wide range of correlated color temperature (CCT) to achieve warm white (CCT = 3600 K) to cool white (CCT = 13,000 K) emission by current modulation from 2.3 A/cm 2 to 12.9 A/cm 2 . It is also demonstrated for the first time that a color rendering index (CRI) as high as 67 can be achieved with such a dichromatic source. The observed CCT and CRI tunability is associated with the spectral power evolution due to the pumping-induced carrier redistribution.

“…This can be done by adjusting electrical properties of the spacer separating blue and cyan QWs in the LED active region [25].…”

Section: Assessment Of Practical Performancementioning

confidence: 99%

Superior color rendering with a phosphor‐converted blue‐cyan monolithic light‐emitting diode

Titkov

Laser & Photonics Reviews

Karpov³

et al. 2016

The future generation of modern illumination should not only be cheap and highly efficient, but also demonstrate high quality of light, light which allows better color differentiation and fidelity. Here we are presenting a novel approach to create a white solid-state light source providing ultimate color rendition necessary for a number of applications. The proposed semi-hybrid device combines a monolithic blue-cyan light emitting diode (MBC LED) with a green-red phosphor mixture. It has shown a superior color rendering index (CRI), 98.6, at correlated color temperature of around 3400 K. The MBC LED epi-structure did not suffer from the efficiency reduction typical for monolithic multi-color emitters and was implemented in the two most popular chip designs: "epi-up "and "flip-chip ". Redistribution of the blue and cyan band amplitudes in the white-light emission spectrum, using the operating current, is found to be an effective tool for fine tuning the color characteristics.