Abstract
Low-frequency noise investigation is a highly sensitive and very informative method for characterization of white nitride-based light-emitting diodes (LEDs) as well as for the evaluation of their degradation. We present a review of quality and reliability investigations of high-power (1 W and 3 W) white light-emitting diodes during long-term aging at the maximum permissible forward current at room temperature. The research was centered on the investigation of blue InGaN and AlInGaN quantum wells (QWs) LEDs covered by a YAG:Ce3+ phosphor layer for white light emission. The current-voltage, light output power, and low-frequency noise characteristics were measured. A broadband silicon photodetector and two-color (blue and red) selective silicon photodetectors were used for the LED output power detection, which makes it possible to separate physical processes related to the initial blue light radiation and the phosphor luminescence. Particular attention was paid to the measurement and interpretation of the simultaneous cross-correlation coefficient between electrical and optical fluctuations. The presented method enables to determine which part of fluctuations originates in the quantum well layer of the LED. The technique using the two-color selective photodetector enables investigation of changes in the noise properties of the main blue light source and the phosphor layer during the long-term aging.
Highlights
Top-quality light sources are of high interest in industrial, science, medicine, military, and daily life applications
We present a comprehensive summary of our investigation of electrical and optical fluctuations, their cross-correlation coefficient of high power (1 W and 3 W) phosphor-converted white Light-emitting diodes (LEDs), and noise characteristics related to LED degradation during long-term aging
We present a summary of the comprehensive investigation of characteristics of the high-power white LED with quantum wells: current-voltage characteristic, light output power and optical spectrum, low-frequency electrical and optical noise properties, and features of the cross-correlation coefficient between optical and electrical fluctuations
Summary
Top-quality light sources are of high interest in industrial, science, medicine, military, and daily life applications. E low-frequency noise components and their locations in the LED structure, and considering that light emission is caused by the charge carrier radiative recombination in the quantum wells, it is convenient to present the electrical voltage fluctuations variance ( ) as the current variance ( ):. To clear up the origins of the low-frequency noise components and their locations in the LED structure, and considering that light emission is caused by the charge carrier radiative recombination in the quantum wells, it is convenient to present the electrical voltage fluctuations variance (σu el) as the current variance (σi2el): σi2el = σu el/R2diff,. Considering that the active photodetector surface area of the photodiode matrix is abouCt o1n6stiidmeersinsgmtahllaetrtthheanactthiveesuprhfaocteodaereteacotof rthseubrfraocaedabraenadopfhtohteopdhetoetcotdoiro(d16e mmmat2r)i,xthise ainbiotuiatl 1m6 etaimsuersedsmoapltliecralthnaonistehelesvuerlfiancethaerefareoqfutehnecybroocatdabvaenodf p(1h0o–t2o0d)eHtezct(oprre(1se6nmtemd 2i)n, tFhieguinrieti9a)l mis eaabsouurted50o0pttiimcaelsnsomisaellleervethl ainntchaenfrbeeqoubetnaciyneodctwavitehotfh(e10w–h20it)eHlizgh(ptrbersoeandtebdanind Fpihgoutroed9e)teisctaobroauttt5h0e0staimmeescusmrreanllte.rStihmainlacralyn, btheeosbhtaoitnneodiswe iitshatbhoeuwt 2h0itteimligehs tsmbraolaledrbwanitdh prhesoptoedctettoectthoer oapt tthicealsaspmeectcruurmrenrat.nSgiemwiliadrtlhy,. the shot noise is about 20 times smaller with respect to the optical spectrum range width
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