Vilius Palenskis

Terahertz responsivity and low-frequency noise in biased silicon field-effect transistors

We report on a comprehensive study of terahertz responsivity and low-frequency noise of current-biased antenna-coupled silicon field-effect transistors. Our measurements corroborate the findings of earlier studies that the current bias dramatically enhances the responsivity by at least an order of magnitude. However, this impressive improvement is accompanied by an equally drastic increase of the spectral density of the voltage fluctuations with the applied current. Therefore, the resulting signal-to-noise ratio (SNR) increases at most by a small amount and only for sub-threshold conditions. We do not register an absolute improvement beyond the best SNR value of the unbiased device. These findings are compared with theoretical absolute-SNR estimates derived using a hydrodynamic transport description. It predicts the maximal enhancement to be limited by a factor of about 1.35. In practical devices, the onset of excess noise suppresses even this little enhancement and limits the applicability of current bia...

Reliability and low-frequency noise measurements of InGaAsP multiple quantum well buried-heterostructure lasers

Analysis of low-frequency noise characteristics is used to investigate the behavior of gain-coupled buried-heterostructure lasers. Devices which exhibit threshold current degradation during electrical and thermal overstress, as well as stable devices, are examined. In addition to examining the magnitudes of the optical and electrical noise as functions of current and frequency, the correlation between the electrical and optical noise is examined. It is shown that unreliable lasers exhibited white electrical and optical noises with negative correlation between them at threshold while the reliable devices did not. While the root cause of these characteristic noise differences is as of yet unknown, the present results suggest the potential utility of noise measurements as a means of predicting laser reliability and the development of low-cost screening techniques.

FLUCTUATIONS OF OPTICAL AND ELECTRICAL PARAMETERS OF DISTRIBUTED FEEDBACK LASERS AND THEIR RELIABILITY

Comprehensive experimental optical and electrical noises and their mutual correlation factor characteristic investigations of distributed feedback (DFB) InGaAsP/InP multiple-quantum well laser diodes (LDs) are presented. At the lasing operation, both optical and electrical noises of DFB LDs are 1/f type and are caused by the defects. Worse operation characteristics and short lifetime of some LDs are caused by the presence of defects in the interfaces with the active region. These defects increase leakage that leads to the larger LD threshold; and, during the ageing, they migrate, form clusters and deteriorate the laser characteristics. Noise characteristics (especially the correlation factor between optical and electrical fluctuations at the threshold) have been found to be suitable for semiconductor lasers quality and reliability prediction.

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.

Experimental investigations of the effect of the mode-hopping on the noise properties of InGaAsP Fabry-Perot multiple-quantum-well laser diodes

Detail studies of the optical and electrical low-frequency noise spectra and their correlation factor of graded-index separate-confinement-heterostructure, multiple-quantum-well (MQW) strained-layer Fabry-Perot (FP) InGaAsP/InP laser diodes have been carried out. It is shown that at defined DC currents and temperatures the intensive Lorentzian-type optical and electrical noise peaks (mode-hopping effect) of the FP lasers may be caused by different effects, since the correlation factor between the noises may be positive, negative, or close to zero, i.e., the diode terminal voltage (or resistance) and light output power can fluctuate in phase, in opposite phases or independently. It is determined that the shift of noise peak due to variation of temperature has an activated character. The activation energy is equal to nearly half the bandgap energy of the barrier layer or region, adjacent to the active region of the laser. It was also shown that coating the FP laser diode mirrors by a thin dielectric layer causes a substantial suppression of the mode-hopping effects, with only a small change of the light output power: i.e., the noise peaks are strongly related to the charge carrier and photon confinement in the active region and neighboring to the active regions.

Nature of low-frequency noise in homogeneous semiconductors.

This report deals with a 1/f noise in homogeneous classical semiconductor samples on the base of silicon. We perform detail calculations of resistance fluctuations of the silicon sample due to both a) the charge carrier number changes due to their capture–emission processes, and b) due to screening effect of those negative charged centers, and show that proportionality of noise level to square mobility appears as a presentation parameter, but not due to mobility fluctuations. The obtained calculation results explain well the observed experimental results of 1/f noise in Si, Ge, GaAs and exclude the mobility fluctuations as the nature of 1/f noise in these materials and their devices. It is also shown how from the experimental 1/f noise results to find the effective number of defects responsible for this noise in the measured frequency range.

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.

Reduction of effective barrier height and low-frequency noise of Al–GaAs Schottky contacts by hydrocarbon ion beam irradiation

Abstract In this study the influence of low energy hydrocarbon ion irradiation at a glancing angle on electronic properties of the GaAs surface and Al–GaAs interface was investigated. The formation of a thin carbon enriched multiphase layer on the GaAs surface was observed. Despite this, reduction of the low-frequency noise, (especially at low temperatures), and effective barrier height of Schottky contacts were achieved at irradiation doses ⩾10 15 ion/cm 2 . The obtained results are explained by the homogenization of the current flow through the Al–GaAs Schottky contact interface layer.

Low-frequency noise and quality prediction of MQW buried-heterostructure DFB lasers

A detailed study of both the optical and electrical low-frequency noise and correlation factor between optical and electrical fluctuation characteristics of single-mode multiple quantum wells (MQW) curied-heterostructure (BH) distributed feedback (DFB) laser diodes has been carried out under a wide current range. These techniques have been used to assess the structural differences between devices that exhibit superior and poor performance and reliability. It has been concluded that for the devices investigated here, the poor device performance characterstics (larger threshold current) and poor reliability are induced by the existence of defects in the interface between the active region and burying laser. These defects generate leakage currents that lead to teh larger threshold current. Defects migration during ageing forms clusters, and this leads to the poor reliability of the lasers. We demonstrate that the low-frequency noise investigations can detect the presence of defects that induce short device lifetime.