Non-destructive analysis on nano-textured surface of the vertical LED for light enhancement

Enhancement of light extraction in Y3Al5O12:Tb3+ thin films through nanopatterning

“…(Kim et al, 2016;Sun et al, 2016) It can occur either by angular randomization of photons by scattering them from a structured surface (Kim et al, 2016;Kumar et al, 2011;Schnitzer et al, 1993;Sun et al, 2016) or by using an intermediate layer with an appropriate refractive index between the AL and the air. (Fang et al, 2013;Khan et al, 2019) In both cases, TIR will be attenuated and LEE value will increase which has been demonstrated on LED chips. (Geng et al, 2014) Among the existing light extraction management strategies based on these principles, one can cite surface roughening (roughened or corrugated substrates) (Kim et al, 2016;Sohn et al, 2004;Youn et al, 2015), photonic crystals (Devys et al, 2014), nanorods or nanopillars (Ding et al, 2017;Yang et al, 2014) and many others.…”

“…It can be ascribed to the growth in opportunities for photons to find broader escape angles with increasing surface roughness. (Khan et al, 2019;Kim et al, 2016) Unstructured amorphous samples are those in which waveguide phenomena are the most present, RMS the weakest and therefore those for which the extraction efficiency is worst. They are transparent under daylight and very smooth, which promoted the waveguiding phenomena.…”

“…(Khanna, 2014;McKittrick and Shea-Rohwer, 2014;Piquette et al, 2016) Even if actually commercialized LEDs-based display and lighting devices are characterized by good photometric parameters, their optical performances can be further improved notably their luminous efficacy. (Geng et al, 2014;Khan et al, 2019) One of the factors we can act on is the Light Extraction Efficiency (LEE), which represents the ratio between the number of photons extracted to the air and the number of photons generated in the active layer. (Geng et al, 2014;Narendran et al, 2005;Tian et al, 2018) Actually, the emitted light is hard to extract into the air since there is a gap between the high refractive index of the phosphor (n~1.8 for the most common used Y 3 Al 5 O 12 :Ce 3+ phosphor) and the air (n~1).…”

Nanostructuration of YAG:Ce Coatings by ZnO Nanowires: A Smart Way to Enhance Light Extraction Efficiency

“…In particular, currently commercialized white LEDs generally associate a semiconductor chip emitting in the ultraviolet or blue wavelength region to one or more phosphor(s) deposited in the form of coatings usually using either on-chip or remote configurations [ 1 , 2 , 3 ]. Even if present LED-based display and lighting devices are characterized by good photometric parameters, they still face technical challenges, among which are their luminous efficacy as well as their lack of light directionality due to the isotropy and incoherence of LED radiation [ 4 , 5 , 6 ]. These drawbacks generally require the use of bulky optics in LED devices to be corrected, which generates additional costs and technical intricacy.…”

“…To reach this objective, several strategies have been developed and reported in the literature. They are based either on the angular randomization of photons by scattering them from a structured surface [ 12 , 13 , 14 , 15 ] or on using an intermediate layer with an appropriate refractive index between the AL and the air [ 4 , 16 ]. In both cases, the TIR will be attenuated and the LEE value will increase, which has been demonstrated on LED chips [ 5 ].…”