Ivan Zulim

Study of the color detection of a-Si:H by transient response in the visible range

A new technique of color detection based on time-resolved charge collection during transient response measurement using a hydrogenated amorphous silicon detector has been proposed and experimentally demonstrated. The method based on the material intrinsic wavelength-filtering properties is implemented in color sensing by transient response of a detector to a combination of basic color light and voltage pulse. Resulting transient responses under different illumination and bias voltage conditions confirm considerable accuracy of proposed method. In particular, the best agreement of measured and calculated transient response curves has been obtained by using the spectral response of all three primary colors in calculations. It was observed that the presence of blue light drastically reduces the transient response to a chromatic light illumination. Finally, a voltage pulse influence to the basic colors transient response was found.

Transient response times of a-Si : H p-i-n color detector

Transients and relevant response times of a-Si : H p-i-n photodetector under various illuminations (in the visible range) and bias voltage conditions were studied. The model/method for possible color detection using on and off transient response times is proposed. Depending on illumination and bias pulse types, one or two processes are found to be involved in the conduction mechanism, including transition and trapping of both charge carrier types. Characteristic photocurrent transients and response times under modulated monochromatic and chromatic visible light illumination enable color recognition. The peculiar behavior of the blue light transients has been also plausibly explained by means of the proposed model

Study of structural changes in krypton implanted silicon

The structural changes induced in single crystal silicon implanted with krypton above the amorphisation threshold were studied by X-ray reflectivity together with grazing incidence small angle X-ray scattering technique. Silicon samples were implanted with krypton with two different ion energies. A well-defined layer of amorphous silicon, 220 nm thick, rich in krypton, was detected below the top, less disturbed layer. The studied series of samples consists of as-implanted, relaxed and several samples with increased level of defects induced by additional Kr implantation. Additional implantation caused changes in layers structure and thickness, which was well evidenced in X-ray reflectivity, while only minor changes of surface roughness and critical angle were detected in GISAXS spectra.

UV light induced defects in amorphous silicon thin films

Abstract The effect of light soaking on a-Si:H films is well known as the Staebler–Wronski effect, though its complete mechanism is not yet clear. We have studied the effect of light soaking with UV light on intrinsic a-Si:H films, as well as the effect of thermal annealing in the dark. It is shown that the light soaking of the films in the air did not affect hydrogen concentration from Si–H bonds and at same time oxidation of the films is observed. It means that oxygen incorporation was due to broken back-bonds to Si–H which are very likely weak bonds. Moreover it is found that UV irradiation produced oxidation and caused even minor Si–H bond-breaking.

The Fourier analysis of a-Si:H photodiode transient response

In this paper, color detection based on the transient response of n-i-p a-Si:H photodiodes to light and voltage pulses was described. The responses to a voltage pulse at constant light and to a light pulse at constant reverse bias voltage were also measured. From the measured dark current as well as the photocurrent, which are both proportional to the instantaneous charge change, the charge was calculated using the FFT method. In the case of transient response to light and voltage pulses, the changeable capacitance as a measure of wavelength dependent light absorption is introduced. The obtained results show the charge increments dependence on wavelength and confirm the p-i-n a-Si:H photodiode as an efficient color detector.

Defects induced in amorphous silicon thin films by light soaking

Abstract The effect of light soaking on a-Si:H films is well known as the Staebler–Wronski effect, though its complete mechanism is not yet clear. The effect of light soaking with UV and white light on intrinsic a-Si:H films was studied. It is shown that device quality a-Si:H films contain a considerable amount of oxygen. The light soaking of the films in the air affected differently low and high-hydrogen a-Si films. It was shown that deep levels in the gap introduced by light soaking are related to oxygen presence. The hydrogen present in the film differently influences the effects of light soaking as a function of its concentration.

Modelling and detection of failure in medical electrodes

In this paper we have studied the failures in medical electrodes such as electroencephalogram electrodes (EEG) being used for collecting brain signals. As those electrodes have to guarantee high level of reliability it is important to explore and predict the possible occurrence of failures in there structure. The electrode tip (needle) made of stainless steel is covered with thin oxide film acting as a dielectric and determing the total electrode resistance. In fact, studying the fluctuations of that resistance gives the insight into defects of the whole structure. The electrical properties of the oxide layer are characterized by charge hopping mechanism and the total resistance could be modeled by implementing random resistance network (RRN) methodology. The applied computational algorithm is based on Monte Carlo simulation procedure with direct and iteration methods. The obtained simulation results show non-gaussian Bramwell-Holdsworth-Pinton (BHP) distribution of the total resistance fluctuations, and they verified by the experiments.

The transient photo-dark current ratio of a-Si:H p-i-n photodiode

In this paper the transient photo-dark current ratios (PDCR)of p-i-n a-Si:H amorphous silicon photodiode on voltage pulse at constant light and voltage pulses were measured and compared. The results show opposite PDCR behaviour of monochrome and chromatic transients in these two cases. From the measured dark current and the photocurrent, which are both proportional to the instantaneous charge change, the charge was calculated using the FFT method. The obtained results show that the depletion charge increments are much smaller than the stored ones.

The a-Si:H p-i-n color detector response time on modulated illumination

Presented in this paper is a study of the visible light detection by the hydrogenated amorphous silicon p-i-n sensor under low reverse bias, where linear increase of photocurrent under different illumination condition is observed. The method based on the material intrinsic wavelength-filtering properties is implemented in color sensing. The response times after switching on and off monochromatic and chromatic illumination at constant reverse bias voltage are analyzed. The results of transient response under different illumination conditions confirm the trap controlled conduction mechanism.

X-Ray Reflectivity and GISAXS Study of Derelaxation in Kr Implanted Si

The structural changes induced in single crystal silicon implanted with Krypton above the amorphisation threshold were studied by X-ray reflectivity together with Grazing Incidence Small Angle X-ray Scattering technique. Silicon samples were implanted with Krypton with two different ion energies. A well-defined layer, 220 nm thick of amorphous silicon, rich in Krypton, was formed below the top, undisturbed layer. A series of samples consist of as-implanted, relaxed, and a number of samples with increased level of defects induced by additional Kr implantation. Additional implantation caused changes in the films composition and thickness, which was well evidenced in reflectivity curve, while only minor changes of surface roughness and critical angle were detected in GISAXS spectra.