Search

Presents a study which reported the results of ellipsometry measurements performed during the growth of hydrogenated amorphous silicon thin films on crystalline silicon substrates. Formation of low-density microstructure in the initial stages of growth; Effect of sputtering on the glow-discharge decomposition of gases; Discussion on the pseudodielectric function trajectories.

In situ and ex situ characterization methods have been applied to investigate the properties of (Ag,Cu)InSe2 (ACIS) thin films. Data acquired from real time spectroscopic ellipsometry (RTSE) experiments were analyzed to extract the evolution of the nucleating, bulk, and surface roughness layer thicknesses. The evolution of these layer thicknesses suggests a transition from Volmer-Weber to Stranski-Krastanov type behavior when Cu is replaced by Ag. The complex dielectric functions of ACIS at both deposition and room temperature as a function of film composition were also extracted from the RTSE data, enabling parameterization of the alloy optical properties. [ABSTRACT FROM AUTHOR]

Optical probes based on polarized light spectroscopy, including spectroscopic ellipsometry (SE) and polarimetry, have been applied in research and process development for the three major' thin-film photovoltaics technologies, including thin-film hydrogenated silicon (Si:H), cadmium telluride (CdTe), and copper indium-galliuiim diselenide (Culn1-xGaxSe2). Real-time SE during materials fabrication has provided insights into the nucleation, coalescence, and structural evolution of these thin films. These insights have led, in turn, to guiding principles for PV performance optimization, as well as future directions for real-time process control. The optical properties deduced simultaneously with the layer thicknesses using real-time SE have been applied to characterize the phase composition of materials (amorphous versus crystalline), the mean free path and grain size, and the relative free carrier concentration. As a result, analytical formulae for the optical properties of PV materials have been developed with free parameters that are linked to basic materials properties. This paper shows how the formulae and associated parameter-property relationships can serve as a database for analyzing complete PV stacks, with future prospects for mapping layer thicknesses and basic materials properties in on-line monitoring applications for large-area PV plates and modules. [ABSTRACT FROM AUTHOR]

A multichannel ellipsometer in the dual rotating-compensator configuration has been developed for applications in real time Mueller matrix spectroscopy of anisotropic surfaces and thin films. The sequence of optical elements for this instrument configuration can be denoted PC[sub 1r](5ω)SC[sub 2r](3ω)A, where P, S, and A represent the polarizer, sample, and analyzer. In this sequence, C[sub 1r] and C[sub 2r] represent the first and second compensators, rotating with angular frequencies of 5ω and 3ω, respectively, where ω=π/T[sub C] is the base angular frequency (corresponding to 2 Hz) and T[sub C]=0.25 s is the fundamental optical period. The instrument can provide 170 point spectra over the wavelength range from 235 nm (5.3 eV) to 735 nm (1.7 eV) in all 16 elements of the unnormalized Mueller matrix with minimum acquisition and repetition times of T[sub C]=0.25 s. In this study, instrumentation calibration procedures are demonstrated in the transmission geometry without a sample, including (i) alignment of the two MgF[sub 2] zero-order biplate compensators, (ii) determination of the retardance and phase spectra for the compensators, (iii) determination of the offset angles for the optical elements, and (iv) characterization of the spectral response function of the ellipsometer. Calibration procedure (iv) allows the (1,1) element of the transmission Mueller matrix to be determined; thus the unnormalized Mueller matrix can be obtained. The dual rotating-compensator multichannel ellipsometer is assessed with respect to its performance in transmission without a sample, and is then applied in the transmission geometry to study anisotropy, depolarization, and light scattering effects for a MgF[sub 2] helicoidally sculptured thin film on a glass substrate. Numerous future applications of this instrument are anticipated for real time analysis of complex surfaces and thin films in the reflection geometry as well. [ABSTRACT FROM AUTHOR]

Submonolayer sensitivity to thin-film nucleation and growth in real time on the millisecond scale has been achieved with a unique rotating polarizer multichannel ellipsometer. Continuous spectra in the ellipsometry angles {ψ(hv),Δ(hv)} consisting of ∼50 points from hv=1.5 to 4.3 eV have been obtained with acquisition and repetition times as short as 16 and 32 ms, respectively. As an example of the instrument capabilities, we present results for hydrogenated amorphous silicon (a-Si:H) growth on c-Si by plasma-enhanced chemical vapor deposition at a rate of 400 Å/min. In this example, the acquisition and repetition times are both 64 ms, and at this speed a precision in (ψ,Δ) of ∼0.02–0.03° is obtained under optimum conditions. We observe a-Si:H nucleation in the first 2 s of deposition, and detect relaxation of nucleation-induced surface roughness with submonolayer sensitivity. [ABSTRACT FROM AUTHOR]

In situ spectroscopic ellipsometry was applied to measure the dielectric functions &eh; of polycrystalline CdTe thin films prepared by magnetron sputtering. The observable critical point (CP) energies determined for the films in best fits to d2&eh;/dE2 are shifted relative to those for single crystal CdTe. The energy shift of the critical point designated as En is attributed to in-plane stress X with linear stress coefficient CX(En). By analyzing these shifts, it was found that stress (1) builds with thickness in as-deposited films, (2) relaxes with increasing substrate temperature at fixed thickness, and (3) is relaxed uniformly in CdCl2 treated films. [ABSTRACT FROM AUTHOR]

The dielectric functions [variant_greek_epsilon] of polycrystalline CdS and CdTe thin films sputter deposited onto Si wafers were measured from 0.75 to 6.5 eV by in situ spectroscopic ellipsometry. Differences in [variant_greek_epsilon] due to processing variations are well understood using an excited carrier scattering model. For each sample, a carrier mean free path λ is defined that is found to be inversely proportional to the broadening of each of the band structure critical points (CPs) deduced from [variant_greek_epsilon]. The rate at which broadening occurs with λ-1 is different for each CP, enabling a carrier group speed υg to be identified for the CP. With the database for υg, [variant_greek_epsilon] can be analyzed to evaluate the quality of materials used in CdS/CdTe photovoltaic heterojunctions. [ABSTRACT FROM AUTHOR]

Real-time spectroscopic ellipsometry (RTSE) is shown to be an effective contactless probe of radio frequency magnetron sputtered molybdenum thin films used as the back electrode in chalcopyrite [Cu(In,Ga)Se2] solar cells. A series of Mo thin films was sputtered onto soda-lime glass substrates at Ar pressures ranging from 4 to 20 mTorr. RTSE measurements reveal how Ar pressure affects the nucleation and growth mechanisms that influence the films’ ultimate grain structure and properties. Determinations of the free electron relaxation times at optical frequencies reveal that higher pressures lead to a smaller average grain size and increased void volume fraction. [ABSTRACT FROM AUTHOR]

Real-time spectroscopic ellipsometry with an ultraviolet-extended spectral range (1.5-6.5 eV) has been applied to investigate the sputter deposition of boron nitride (BN) thin films with high cubic content in terms of a two-layer optical model. In this model, the inner and outer layers represent sp[sup 2]- and sp[sup 3]-bonded BN (hBN and cBN), respectively. The thickness evolution of the two layers as well as their dielectric functions over the extended spectral range have been determined. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous carbon film growth in diamond-like and polymer-like forms has been studied by in situ ellipsometry. The experiments provide accurate values of the optical functions, thickness, and deposition rate in real time. Reactions between the substrate and the gas phase species or film in the initial stages of growth, inaccessible to ex situ probes, have been detected with monolayer resolution. Monolayer changes in near-surface bonding have also been detected. [ABSTRACT FROM AUTHOR]