Crystallization of phosphorus-doped amorphous silicon films prepared by glow discharge decomposition of silane

Crystallization kinetic of phosphorus-doped amorphous silicon films prepared by glow discharge of silane is observed by using conductivity measurements. The activation energy Ev of the growth rate V g is deduced as a function of doping level Cp (ranging from 0.05 to 5 %). Ev has a constant value equal to 3 eV for Cp ≤ 0.5 % and increases for higher values of Cp. We compare these results with Csepregi et al.'s ones, obtained by channeling. They obtain Ev equal to 2.4 eV in the whole doping level range.La cristallisation dans le silicium amorphe dopé au phosphore, et obtenu par décomposition de silane, a été observée en utilisant les mesures de conductivité électrique. Ceci nous a permis d'obtenir l'énergie d'activation E v de la vitesse de croissance Vg en fonction de la concentration du dopage Cp (variant de 0,05 à 5 %). On trouve une énergie Ev égale à 3 eV pour Cp ≤ 0,5 %. Cette énergie augmente pour des concentrations de dopage supérieures. Ces résultats sont comparés avec ceux obtenus par Csepregi et al. en utilisant la méthode de canalisation. Ils obtiennent une énergie Ev indépendante du dopage et égale à 2,4 eV

Effect of the hydrogen dilution on the local microstructure in hydrogenated amorphous silicon films deposited by radiofrequency magnetron sputtering

The nature of the hydrogen bonding and content and their influence on the film microstructure have been investigated in detail, as a function of the H2 dilution and the residual pressure, in hydrogenated amorphous silicon (a-Si:H) films prepared by radiofrequency (rf) magnetron sputtering at a common substrate temperature (~ 250 °C) and pressure (5 × 10−4 torr) and high rates (11−15 Å/s). H2 percentages in the gas phase mixture (Ar + % H2) of 5, 10, 15 and 20% have been introduced during growth. For the 20% of H2, two different pressures of 5 × 10−4 and 50 × 10−4 torr were used. A combination of infrared absorption, optical transmission and elastic recoil detection analysis experiments have been carried out to fully characterize the samples in their as-deposited state. The results clearly indicate that for H2 percentage equal to or lower than 15% , the total bonded H content in the films increases as the H2 percentage increases, and then reaches a saturation value or even decreases for higher H2 percentage. Moreover, the microstructure is also found to be deeply affected by the H2 dilution and pressure. In particular, for high H2 percentage (20%) and high pressure (50 × 10−4 torr), unbounded H as well as polyhydride (Si-H2)n chains, possibly located in structural inhomogeneities such as voids, are also present in the films in addition to the isolated monohydride Si-H and polyhydride Si-H2 complexes. As a result, a reduction of the compactness of the film structure associated with a decrease of the refractive index n is observed. The optical gap is found to be rather controlled by the total bonded hydrogen content. The lowest proportion of isolated polyhydride Si-H2 complexes and the highest density are observed for films deposited with 10% of H2 in the gas phase and a pressure of 5 × 10−4 torr

A THEORETICAL STUDY OF HYDROGEN EXODIFFUSION IN a-Si : H, COMPARISON WITH CONDUCTIVITY MEASUREMENTS

Hydrogen evolution in a-Si : H prepared by glow discharge decomposition of silane has been studied previously as a function of annealing temperature, using nuclear reaction, conductivity (σ) and Electron Paramagnetic Resonance (EPR) measurements. Conductivity measurements show the existence of a surface dehydrogenated layer (SDL) for T ⩾ 500 °C. We presented a theoretical kinetic model which takes into account the existence of two kinds of site for hydrogen in the amorphous network : one site is a center from which hydrogen can diffuse, the other is a tightly bound center (corresponding to isolated Si-H bonds). This theoretical model is used here to interpret our conductivity measurements (which are sensitive to the departure of H in the Si-H configuration) for annealing temperatures above 500 °C. This allows us to describe quantitatively the SDL in the same temperature range. We then deduce the thermodynamic parameters which characterize the breaking of the isolated Si-H bond, and the possibility of trapping of a hydrogen by a Si-dangling bond. We obtain the corresponding activation energies respectively equal to 3.3 eV and 4 eV. We thus confirm the value of the Si-H bond energy and give the capture energy of a hydrogen in an isolated Si-dangling bond, which has not been previously determined

STRUCTURAL AND ELECTRONIC PROPERTIES OF CVD SILICON FILMS NEAR THE CRYSTALLIZATION TEMPERATURE

Nous avons examiné les propriétés structurales de films déposés par C.V.D. dans la gamme de température 600-750°C avec une attention particulière sur la répartition en volume des cristaux pour les films déposés autour de la température de cristallisation. Nous démontrons que le mécanisme général de cristallisation déterminant la structure est celui de dépôt de matériau amorphe suivi de cristallisation dans la phase solide pendant la durée du dépôt. Ce processus dans la phase solide apparaît par une nucléation prédominante à l'interface film-substrat. Les implications de ceci sur la morphologie et les propriétés physiques des films seront discutées.We have examined the structural properties of films grown by CVD in the range of temperatures 600-750°C. with particular emphasis on the volume repartition of crystals for films deposited around the crystallization temperature. We find that the general crystallization mechanism which determines the structure is one of deposition of an amorphous material followed by subsequent solid phase crystallization during the deposition time. This solid phase process occurs through a dominant nucleation at the film-substrate interface. The implications of this on the physical properties and morphology of these films will be discussed

Influence of the deposition conditions on the optoelectronic properties of R.F. magnetron sputtered a-Si:H films

We have studied the effect of the deposition conditions on the hydrogen incorporation modes and content and their effects on the optoelectronic properties of three different series of a-Si:H films prepared by R.F. magnetron sputtering at high substrate temperature (250 °C) and high deposition rates (~ 10 Å/s). We have correlated infrared absorption measurements with optical transmission and Photothermal Deflection Spectroscopy (PDS) experiments. The samples were characterized successively in their as-deposited state and after annealing at a temperature around 180 °C. The results indicate that the modes of H incorporation as well as the hydrogen content in the three series are completely different from those observed for the samples prepared by Plasma Enhanced Chemical Vapour Decomposition of pure silane (P.E.C.V.D.) at the same substrate temperature. The microstructure of the films is also different. The density of deep defects measured in the as-deposited is slightly higher in the former case. This density decreases significantly after annealing at 180 °C and becomes comparable to that obtained for a-Si:H samples prepared by P.E.C.V.D. at 250 °C at low deposition rates (~ 1 Å/s), with however a higher disorder in the R.F. sputtered films

Junction capacitance measurements for the determination of the density of gap states in hydrogenated amorphous silicon

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Détermination de la taille et de la concentration de cristallites dans une couche amorphe par mesure de conductivité

On rappelle comment la fraction cristallisée peut être obtenue à partir d'une mesure de conductivité. On montre brièvement comment la vitesse de croissance, la taille et la concentration des cristallites peuvent être déterminés en étudiant la cinétique de cristallisation, suivant que celle-ci est induite en surface ou en volume, dans le cas où il n'y a pas nucléation homogène. On présente des résultats expérimentaux pour des couches de germanium amorphe

Effect of the hydrogen dilution on the short-range and intermediate-range-order in radiofrequency magnetron sputtered hydrogenated amorphous silicon films

Raman spectroscopy experiments correlated with infrared absorption, optical transmission and photothermal deflection spectroscopy ones are used to investigate in detail the short-range-order (SRO) and intermediate-range-order (IRO) in hydrogenated amorphous silicon (a-Si:H) films elaborated at high rates (~15 Å/s) by radiofrequency magnetron sputtering with various hydrogen dilution percentage (5 to 20%), leading to different hydrogen-related microstructure and content. The analysis of the transverse optic (TO)- and transverse acoustic (TA)-like modes of the Raman spectra indicates that both, the SRO and IRO are more strongly dependent on the nature of hydrogen bonding configurations, namely the relative proportion of polyhydride Si-H2 and (Si-H2)n complexes and/or clustered monohydride (Si-H)n groups incorporated in the films, rather than on the total bonded hydrogen content. The increase observed in the line width of the TO- and TA-like modes are well correlated with that of the disorder parameter E0, also called Urbach edge parameter, which is related to the exponential absorption from the valence band tails states distribution. Moreover, the analysis of the optical transmission data clearly evidences that the dispersion energy Ed and the static refractive index n0 are also maximum for films having the lowest value of E0, suggesting that they exhibit the highest mean coordination number and compactness respectively, consistent with better SRO and IRO