Sandra Pralgauskaitė

A DETAIL ANALYSIS OF ELECTRICAL AND OPTICAL FLUCTUATIONS OF GREEN LIGHT-EMITTING DIODES BY CORRELATION METHOD

A detail analysis of electrical and optical fluctuations of large power (1 W) green light-emitting diodes (LEDs) is presented. Special attention was directed to measurement and interpretation of correlation coefficient between electrical and optical fluctuations. The correlation coefficient was measured not only over frequency range from 10 Hz to 20 kHz, but also in every one-octave frequency band by using digital filters. It is shown that correlated part of electrical and optical fluctuations for investigated green LEDs is related with random potential fluctuations of parameters of quantum well due to charge carrier capture by the defects in the active layer, while uncorrelated part of electrical noise is caused by parallel leakage channel which resistance is many times higher than that of p-n junction.

NOISE CHARACTERISTICS AND RELIABILITY OF LIGHT EMITTING DIODES BASED ON NITRIDES

Optical and electrical noises and correlation factor between optical and electrical fluctuations of nitride-based light emitting diodes (LEDs) have been investigated under forward bias. Their electrical, optical and noise characteristics were compared with ones of LEDs of other materials. LED noise characteristic changes during aging have been measured, too. It is found that optical and electrical noise spectra under forward bias for more reliable LEDs distinguish by lower l/f type fluctuations and Lorentzian type noise at higher frequencies. LEDs with intensive 1/f noise demonstrate shorter lifetime. It is shown that reason of LED degradation is related with defects presence in device structure. These defects can be formed during device fabrication or appear during operation. An analysis of LED current-voltage and electrical noise characteristics under forward and reverse bias has shown that LEDs with intensive 1/f electrical noise, large reverse current (low reverse breakdown voltage) and larger terminal voltage under forward bias distinguish by short lifetime.

Low-frequency noise properties of beryllium δ-doped GaAs/AlAs quantum wells near the Mott transition

Noise properties of beryllium delta-doped GaAs/AlAs multiple quantum wells, doped both above and below the Mott transition, are studied within the frequency range of 10 Hz−20 kHz and at temperature from 77 K to 350 K. It is shown that the generation-recombination noise in structures close to the Mott transition exhibits two peaks—a frequency and temperature-dependent peak between 120 and 180 K and a broadband, frequency- and temperature- nearly independent peak around 270 K. Activation energies are estimated; origin of the broadband maximum is attributed to holes tunnelling into defect trap states located in the AlAs barrier/GaAs quantum well interface.

ANALYSIS OF NOISE CHARACTERISTICS OF GaAs TUNNEL DIODES

An analysis and investigation of noises of GaAs tunnel diodes, which abrupt p+-n+ profile was obtained by using amphoteric nature of silicon, were performed. The main scope of this work was to verify the concepts of the explanation of white noise characteristics on the ground of shot noise and on the ground of the Gupta theorem of thermal noise in resistive elements. The other scope was to investigate the peculiarities of low frequency noise in p+-n+ junctions formed by using amphoteric silicon nature.

Reliability investigation of light-emitting diodes via low frequency noise characteristics

Abstract Investigation of changes of operation and noise characteristics during aging process of light-emitting diodes (LEDs) has been carried out. Several groups of different design (different optics) LEDs based on different materials (nitride-based blue and white LEDs, phosphide-based red LEDs) have been investigated. It is found that leakage current components appear due to LED’s defects and their affect is observed as increase of both the low frequency electrical noise intensity and non-ideality factor of current-leakage characteristic in small current region. No considerable changes of light intensity characteristics during LEDs aging have been observed. Noise modeling, spectral and correlation analysis of optical and electrical fluctuations show on partly correlated optical and electrical fluctuations caused by defects in the active region of the LED. Degradation processes of investigated LEDs foremost occur in the diode chip and lead to the leakage current that has important affect to the electrical fluctuation level, but practically has a weak influence to the light emission properties of LED. Phosphorous layer of white LEDs and additional optical elements have no significant influence to the reliability of investigated LEDs under given aging conditions.

Noise characteristics and reliability of high power white light emitting diodes based on nitrides

High power white light emission diode reliability and aging processes have been investigated. Optical, electrical and noise characteristics have been carried out for initial devices and during their aging. Analysis of noise characteristics help revealing of light emission diode aging processes and reliability problems. It is found that optical and electrical noise spectra changes reflect light emission diode aging. Noise characteristics, especially correlation factor between optical and electrical fluctuations, and current-voltage characteristics at low bias reveal physical processes that take place during investigated device aging and rapid its degradation. It is shown that reason of high power light emission diode degradation is related with defects presence in the device structure. Additional defects appear during LED operation and lead to the leakage current and non-radiative recombination increase.

Fluctuations of Optical and Electrical Parameters and Their Correlation of Multiple-Quantum-Well INGAAS/INP Lasers

Low-frequency noise characteristics of Fabry-Perot (F-P) and distributed feedback, ridge-waveguide and buried-heterostructures InGaAsP/InP multiple-quantum-well lasers investigation has been carrier out. Mode hopping effect characteristic for F-P laser operation is caused by carrier gathering in barrier and cladding layers, and intensive optical and electrical noise during mode hopping is related with recombination in these layers. Defective laser diodes structures can be revealed by noise characteristic investigation, especially the correlation factor is more informative at threshold.

Resistivity and low-frequency noise characteristics of epoxy-carbon composites

Noise and electrical transport properties of composites based on epoxy resin filled with various carbon inclusions (single-walled carbon nanotubes, high surface area carbon black, and exfoliated graphite) were investigated in depth. The temperature dependence of resistivity shows that Motts hopping and tunneling between conductive carbon particles dominate the charge carrier transport at low temperature, whereas a positive temperature coefficient effect occurs at higher temperature. Low-frequency noise spectra of the investigated materials comprise 1/fα type components. The noise level is the highest for composites close to the percolation threshold. The percolation threshold value of the system also strongly impacts both the temperature dependence of the noise level and the resistivity. Close to the percolation threshold, the noise level increases due to the carrier tunneling throughout the polymer matrix and decreases due to the rapid expansion of the polymer matrix. In contrast, the latter has almost ...

Noise characteristics and reliability of light emitting diodes based on nitrides

Optical and electrical noises and correlation factor between optical and electrical fluctuations of nitride-based light emitting diodes (LEDs) have been investigated under forward bias. Their electrical, optical and noise characteristics were compared with ones of LEDs of other materials. LED noise characteristic changes during aging have been measured, too. It is found that optical and electrical noise spectra under forward bias for more reliable LEDs distinguish by lower 1/f type fluctuations and Lorentzian type noise at higher frequencies. LEDs with intensive 1/f noise demonstrate shorter lifetime. It is shown that reason of LED degradation is related with defects presence in device structure. These defects can be formed during device fabrication or appear during operation. An analysis of LED current-voltage and electrical noise characteristics under forward and reverse bias has shown that LEDs with intensive 1/f electrical noise, large reverse current (low reverse breakdown voltage) and larger terminal voltage under forward bias distinguish by short lifetime.

InGaAsP laser diode quality investigation and their noise characteristics

Electrical and optical low frequency noise characteristics of different quality InGaAsP Fabry-Perot and distributed feedback buried-heterostructure 1.55-μm laser diodes with the multiple-quantum-well active region are investigated keeping in view the use of the peculiarities of the characteristics for the assessment of the quality and reliability of LDs. The noise characteristics are shown to give the most informative result when measured at the threshold. In parallel to the noise measurements the current-voltage characteristics are measured and analyzed. In the use of this combination an alternative to the reliability tests by accelerated aging is seen. The mode hopping effect exhibited by the Fabry-Perot laser diodes is suppressed by the facet coating with an antireflection layer.