Jean Eric Bourée

Complete Mueller matrix measurement with a single high frequency modulation

Abstract A new Mueller matrix ellipsometer (MME) is presented. It provides the simultaneous measurement of the 16 Mueller matrix coefficients in four modulation periods (80 μs under the present conditions). This system is accurate (error≤1%), robust since there are no moving parts, enables low-light-level measurements without a chopper and lock-in amplifier and can be easily used for real time measurements. The setup is based on the polarization modulator–sample–polarization detector configuration. The polarization modulation is provided by a coupled-phase-modulator (CPM) which uses two identical phase-locked electro-optic phase modulators operating at 50 KHz. With the introduction of a coupling object between the two phase modulators, the four Stokes parameters of the light beam, including the intensity, are independently modulated on the basis of the first and second complex harmonics of the modulation signal. The polarization of light, after interaction with the sample, is measured with a multichannel division of amplitude polarimeter (DOAP). This DOAP is based on a slightly beveled amorphous-silicon (a-Si) coated glass plate. The high index of refraction contrast between a-Si and SiO2 provides an efficient polarimeter, less sensitive to the angle of incidence than usual dielectric-coated ones. The spectroscopic capability of the MME is illustrated by preliminary measurements of depolarization effects at two laser wavelengths: He–Ne at 632.8 nm and Ar at 488 nm.

The grain size in microcrystalline silicon: correlation between atomic force microscopy, UV reflectometry, ellipsometry, and X-ray diffractometry

The grain size in polycrystalline silicon thin films is approached through X-ray diffractometry, UV optical properties, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The apparent discrepancy by two orders of magnitude between SEM and X-ray sizes is resolved by AFM which reveals the existence of substructures. Very satisfying correlations are established between the different approaches. The X-ray derived mean crystal size is shown to be the relevant size and corresponds to the smallest crystals observed in microscopy.

Electronic properties of silicon thin films prepared by hot-wire chemical vapour deposition

Abstract A transition from amorphous to microcrystalline silicon occurs in hot-wire chemical vapour deposition silicon films with increasing dilution of silane with hydrogen. This transition is detected for a dilution ratio R = [SiH 4 ]/[H 2 ] between 10% and 9%, where [SiH 4 ] and [H 2 ] are the silane and hydrogen flow rates, by Raman and optical absorption spectra, and by dark conductivities which are several orders of magnitude larger in microcrystalline as compared to amorphous films. In the microcrystalline films we observe a simultaneous increase of both majority and minority carrier mobility-lifetime products with increasing hydrogen dilution, which is consistent with the measured decrease in sub-gap absorption and defect density deduced from transient photocurrent measurements. This simultaneous increase is in contrast with the general trend observed in amorphous films, where these two quantities vary in opposite ways, and are associated with an improvement of the transport properties of the material. The microcrystalline samples did not show light-induced degradation after prolonged illumination.

Dual-mode radio frequency/microwave plasma deposition of amorphous silicon oxide thin films

A new dual-plasma (surface wave-coupled microwave and capacitively-coupled radio frequency) plasma enhanced chemical vapor deposition reactor for high growth rate deposition of amorphous insulating alloys has been developed. A high degree of flexibility for thin film material synthesis is expected, because the energy of the ion bombardment can be controlled independently of the microwave plasma chemistry. In situ spectroscopic ellipsometry is used for the optimization of the dual-mode plasma deposition of hydrogenated silicon oxides a-SiO x:H (with 0 < x < 2) providing monitoring of the index of refraction and deposition rate. A new procedure for the real-time calculation of both parameters is reported. The growth rate of nearly stoichiometric oxides increases as a function of the oxygen flow rate with a maximum value of 33 As -1 using a 315 W microwave power.

Photoluminescence intensity and anisotropy decays in amorphous carbon

The decays of intensity and anisotropy of UV-excited photoluminescence PL in hydrogenated amorphous carbon have been investigated in the ps-ns time range. For emission energies E between 1.8 and 3.5 eV, anisotropy decreases within em . 100 ps and reaches a plateau within 1 ns. The emission anisotropy plateau value increases from 0.02 to 0.12 and the decay . time of PL intensity decreases from 1 ns to 40 ps as E increases. The exponential increase of time-averaged anisotropy em as E increases is explained by a competition between exciton decay and randomization of polarization due to electronic em

Electronic properties and device applications of hot-wire CVD polycrystalline silicon films

Polycrystalline silicon films (5 to 30 {micro}m thick) have been deposited on glass substrates at low temperatures (400--550 C) with a rate of 15 {angstrom}/s by hot-wire chemical vapor deposition (HWCVD). The homogeneity of the deposited layer is {+-}5% on a 8 cm diameter substrate. The films have columnar microstructure and a textured surface. The undoped films (carrier concentration, 10{sup 11} cm{sup {minus}3}) have a resistivity of 10{sup 5}-10{sup 6} {Omega}-cm, activation energy of 0.50{+-}0.05 eV and Hall mobility of 14&4 cm{sup 2}/V.s. By in situ gas phase doping, resistivity can be varied by six to seven orders of magnitude. Incorporation of dopant atoms such as boron into the film, strongly influences its morphological and crystallographic structure. The mobility lifetime product of undoped films is low (10{sup {minus}8} cm{sup 2}/V), possibly due to the presence of a high density of dangling bonds defects and broad band-tails. This product can be improved by a factor of 5 to 10 by using in-situ hydrogen passivation in the same reactor at lower temperature (350--400 C) within one hour. The results of many complementary experiments suggest that hydrogen treatment mainly improves carrier mobility by a factor of 3 to 4 by passivating extended defects.morexa0» Preliminary results on application of these types of materials in unoptimized P-I-N solar cells on c-Si and glass substrates are presented.«xa0less

Photoluminescence of polymer-like amorphous carbon films grown in different plasma reactors

The visible photoluminescence (PL) properties (emission and excitation spectra) of hydrogenated amorphous carbon (a-C:H) have been investigated for polymer-like thin films grown at low substrate temperature and small ion energies. For a large number of a-C:H films grown in three reactors (dual-mode plasma, radio frequency plasma and electron cyclotron resonance plasma) the emission spectra appear as a sum of three peaks with energies (a) 2.28 eV, (b) 2.65 eV and (c) 2.95 eV, being independent of the excitation energy (3.54 eV or 4.13 eV). Their relative intensities depend on the growth parameters while their positions are almost independent. Preliminary picosecond time-resolved PL data indicate a decrease of the decay time for increasing emission energies. A two-phase model of a-C:H is proposed to explain the PL excitation spectra.

Influence of low energy argon plasma treatment on the moisture barrier performance of hot wire-CVD grown SiNx multilayers

The reliability and stability are key issues for the commercial utilization of organic photovoltaic devices based on flexible polymer substrates. To increase the shelf-lifetime of these devices, transparent moisture barriers of silicon nitride (SiN x) films are deposited at low temperature by hot wire CVD (HW-CVD) process. Instead of the conventional route based on organic/inorganic hybrid structures, this work defines a new route consisting in depositing multilayer stacks of SiN x thin films, each single layer being treated by argon plasma. The plasma treatment allows creating smoother surface and surface atom rearrangement. We define a critical thickness of the single layer film and focus our attention on the effect of increasing the number of SiN x single-layers on the barrier properties. A water vapor transmission rate (WVTR) of 2 10 %4 g/(m 2 &day) is reported for SiN x multilayer stack and a physical interpretation of the plasma treatment effect is given.

Photoconductive polycrystalline silicon films on glass obtained by hot-wire CVD

Textured polycrystalline silicon films with columnar structure have been deposited on glass at low temperature (400--550 C) and high deposition rate (10 to 15 {angstrom}/s) by hot-wire chemical vapor deposition using SiH{sub 4}-H{sub 2} gases. The homogeneity of the deposited layer is {+-}5% on a 8 cm diameter. As deposited films have a poor photoconductivity. However hydrogen confinement in the films during the deposition or after the deposition is found to be the key for obtaining {micro}c/poly-Si with a significant diffusion length. Eventually reasonable values of the mobility lifetime product (>10{sup {minus}7} cm{sup 2}/V) are obtained by in situ hydrogen passivation of poly-Si films after deposition. Efficient shifting of the Fermi level is achieved by in situ B or P doping. The incorporation of boron in poly-Si network strongly influences the morphology and the crystalline structure. Undoped films have a Hall mobility of 14 {+-} 5 cm{sup 2}/V.s which decreases versus the carrier concentration.

GROWTH MECHANISMS OF ALUMINUM DOTS DEPOSITED BY LASER-INDUCED DECOMPOSITION OF TRIMETHYLAMINE ALANE

Aluminum dots have been deposited by thermal decomposition of trimethylamine alane (TMAA) on silicon substrates irradiated with a tightly focused argon ion laser beam (λ=514 nm). Carbon free Al deposits containing less than 5 at.% of impurities (mainly oxygen) detected by Auger Electron Spectroscopy were grown. The growth kinetics of Al dots was investigated as a function of TMAA pressure and laser-induced temperature. The deposition of dots occurred at a laser-induced temperature as low as 210°C. The TMAA decomposition was thermally activated (activation energy of 18 kcal/mole) and the deposition rate at 300°C was equal to 2 µm/s. The effects of H2 or He (used as buffer gases) in the gas phase on the growth kinetics of dots was also studied. The growth mechanisms of dots are discussed and proposed on the basis of the results of this kinetic study.