Amorphous Silicon solar cells have been produced by a two consecutive decomposition and deposition chamber system, using polished S. S. substrates. Through a systematic investigation of the electrical and optical properties of doped and undoped amorphous silicon layers (1) we observe that the deposition conditions (gas partial pressure, density of r. f. power, substrate temperature, electromagnetic static fields applied to the substrate, and gas flow rate) influence films properties. In the course of this investigation we have been studying the role of the sheet resistance, R//s, of the I. T. O. layer on the short circuit current, I//s//c, and on the open circuit voltage, V//o//c, of p. i. n. structures of 16cm**2 in area. The obtained results indicate that V//o//c is almost independent on R//s, while I//s//c variation approaches a square root dependence on R//s.

This new production technique is based on the growth of a-Si films on a reactor where gas decomposition promoted by a capacitively coupled r. f. power system takes place in a chamber separated from that where amorphous films are deposited under the action of an electromagnetic static field. Using this method, we shall reduce films contamination caused by the residual gas desorbed from reactor walls. At the same time, there is a reduction plasma ion and electron damages on the deposited films. The main species impinging upon our substrates will be mainly composed of long life radicals with high mobilities and high diffusion rates, which will give origin to a random silicon network free of long poly-silane chains.

The current transport in metal-amorphous semiconductor barriers is examined by solving the proper Poisson's equation and transport equations within the semiconductor's space charge region taking into account the role of trap shallow states distribution function. The effect of metal is also included through appropriate boundary conditions of the above solutions. Generalized transport equations will be derived either when thermionic drift-diffusion emission process dominates or when the conduction mechanism is mainly due to drift-diffusion emission. Both situations will be analysed with or without neglecting carriers losses during their collision free path, from which a tractable expression for the current-voltage characteristic will be determined.

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This paper deals with the interpretation of transport properties of amorphous silicon hydrogenated films (a-Si:H) through dark conductivity, photoconductivity and pulse controlled capacitance-voltage measurements. a-Si:H films were produced by rf glow discharge coupled either inductively or capacitively to a 3% SiH4/Ar mixture at different crossed electromagnetic static fields. The data concerned with the dark activation energy, photoactivation energy, variation of the density of localized states and photosensitivity, (σph/σd)25°C, of a-Si:H films can account for their optoelectronic properties which are strongly dependent on the deposition parameters. We also observed that crossed electromagnetic static fields applied during film formation influences hydrogen incorporation in a different manner than previously proposed. © 1983.

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A sociologia tem como objecto de análise a acção social e a sua expressão nas relações sociais. Estas relações estão organizadas de múltiplas formas, e conhecem infinitos tipos de interacções humanas. No entanto, o conjunto de relações em que os indivíduos se opõem ou criam laços de solidariedade fundamenta-se e verifica-se na esfera da produção. É efectivamente neste domínio que a conduta humana encontra uma das suas mais importantes determinações. Assim, o desenvolvimento da organização industrial acabou por fornecer verdadeiramente algumas das características essenciais da sociedade moderna. Uma delas é o fenómeno da especialização que se acentuou particularmente na indústria e acabou por abraçar praticamente todos os outros domínios da actividade humana.

The aim of the present work was to study the optical properties of amorphous hydrogenated silicon films produced by capacitive and inductive r.f. glow discharge in a 3%SiH4-Ar gas mixture. The effect of the application of static electric and magnetic fields during the film formation on the photoconductivity, photoactivation energy, recombination mechanisms and optical gap was thoroughly investigated. Films prepared in a capacitively or inductively coupled discharge show bias-dependent photoconductivities, which reach about 10-4 Ω-1 cm-1 for an inductive discharge with a negative bias and about 10-5 Ω-1 cm-1 for a capacitive discharge with a positive bias. The optical gap is of the order of 1.55 eV for capacitive films and is bias dependent for inductive films (1.45-1.85 eV). A superimposed magnetic field (of about 1 kG) increases the photoconductivity by one order of magnitude for both deposition methods. The optical gap is field dependent for inductive films (1.6-1.8 eV) and is about 1.6 eV for capacitive films. The main recombination mechanism at a moderate photon flux (less than 1014 cm-2 s-1) is monomolecular for all deposition conditions. The photoactivation energy lies between 0.1 and 0.2 eV for capacitive films and is about 0.1 eV for inductive films. It was also found that, by using suitable crossed electric and magnetic fields, it was possible to control the density and nature of the defect states in the films. These are correlated with the type of hydrogenated silicon species and with the amount of hydrogen incorporated into the films, which markedly influence the film properties. © 1982.

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International project (1251?78 and 1252?78) in which the Technical University of Sofia (S.Valtchev, N.Stefanov) has sucessfully acomplished the task of constructing and implementing in production a high precision (0.01% regulation) power supply for a cirurgical laser tool (1977-1980). The construction involved a vacuum tube cascaded with MOS-FET to obtain very high quality current source necessary for the stable characteristics of the gas discharge in the laser tube.

It is shown that the electronic properties of amorphous germanium (a-Ge) prepared by the glow-discharge decomposition of germane can be controlled systematically by substitutional phosphorus doping from the gas phase. Specimens with different doping levels have' been investigated by conductivity, thermoelectric power and Hall effect measurements in a temperature range between 160 and 450 K. The dependence of conductivity on doping level is qualitatively similar to that in a-Si, but the range of control is limited in a-Ge by the smaller mobility gap. Also the larger overall density of gap states in this material reduces the doping sensitivity. The above transport measurements and their temperature dependence can be interpreted in a quantitatively consistent manner- by a two-path model in which conduction takes place in the extended states and in another path through the localized states. As 111 a-Si, the photoconductivity of glow-discharge Ge can be appreciably sensitized by phosphorus doping. The μτ product deduced from such experiments on a-Ge and a-Si are compared for different preparation techniques. The data show that irrespective of the presence of hydrogen the method of deposition remains an important factor in determining the density of gap states. © 1979 Taylor & Francis Ltd.

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