| Abstract [eng] |
The aim of the dissertation was to investigate quality and reasons of degradation of modern InGaN high brightness light emitting diodes (LEDs) via low frequency noise characteristics. Current-voltage, light intensity dependency on LED current, electrical and optical noise (10 Hz – 20 kHz) and cross-correlation between optical and electrical fluctuations characteristics were measured. Additionally cross-correlation factor between optical noises from the active region and from the YAG:Ce+3 phosphor layer was measured for white light emitting diodes. There was found that origin of LED degradation is growth of number of non-radiative recombination centers in its structure. The largest influence to the LED quality and reliability is by the active region. The first signs of LED degradation appear in electrical noise, cross-correlation factor and current-voltage (at small current) characteristics. The technique that enables decomposition of experimentally measured noise spectra into the separate noise components of different spectrum type was explained in details. It was found that 1/f type noise has the largest contribution to the total cross-correlation factor, when 1/f type noise is not completely correlated. 1/f1,5 type noise is completely correlated but its influence to the total cross-correlation factor is significant only at low frequencies. |
