Previous lH NMR and IR studies of six samples of μc-Si:H prepared under plasma excitation frequencies ranging from 13 MHz to 95 MHz and silane concentrations ranging from 3% to 8% revealed three important results: (1) for a fixed plasma excitation frequency (95 MHz) the hydrogen content increases with silane concentration; (2) for fixed silane concentration the hydrogen content is roughly constant over a wide range of plasma excitation frequencies; and (3) the 1H NMR free induction decay exhibits beat frequencies which correspond to the calculated frequencies due to SiH2 in microcrystalline silicon. In this study we investigate the role of SiH2 in the μc-Si:H structure using 1H NMR measurements. We studied two samples prepared at two different plasma excitation frequencies (13 MHz and 95 MHz). The lU NMR lineshapes of these samples were measured at 300 K and 77 K. The motionally narrowed component of the 1H NMR is not as rapid at room temperature as that observed previously, but the linewidth of this component increases significantly at 77 K. Because of this difference between our results and those reported previously, it is possible that H2 molecules are not responsible for the motional narrowing in our samples. We present plausible arguments for the hindered motion of SiH2 groups in our μc-Si:H samples.

We investigated the possibility to use the photoluminescence (PL) emission at room temperature for the characterization of grain boundary and surface passivation of μc-Si and single crystalline silicon. The PL-spectra of c-Si and μc-Si taken at 300 K consist of an emission band around 1.1 and 1 eV, respectively. Measuring the PL intensity we study the influence of electrochemical and plasma passivation by hydrogen. We compare the behavior of the films to that of Si crystals. In this case the PL intensity is high for a well H-terminated c-Si surface and decreases during cathodic polarization (hydrogen evolution) which points to the formation of additional non-radiative recombination centers. Whereas the PL intensity of the as prepared μc-Si films is unchanged, that of the annealed films increases during hydrogen evolution indicating the electrochemical passivation of defects on grain boundaries.

We have reported for the first time on visible photoluminescence (PL) in crystallized a-Si:H/a-SiNx:H multilayer structures by CW Ar ion laser annealing treatments. In this paper we present new results on visible PL from crystallized a-Si:H by using KrF excimer pulse laser (wavelength 248 nm) irradiating treatments. The transmission electron microscopy and Raman scattering studies reveal the microstructures of crystallized Si films, which depend on the pulse number and the pulse energy density of KrF laser. When the laser pulse energy density is higher than 520 mJ/cm2, the nanosized Si crystallites (nc-Si) can be formed from a-Si:H layers with a thickness of 100 nm and strong PL with a peak wavelength of 610 nm has been observed at room temperature.

Visible photoluminescence at 1.62 eV has been observed at room temperature from fluorinated and hydrogenated nanocrystalline silicon (nc-Si:H,F) produced in a typical plasma enhanced chemical vapor deposition system. The use of SiF4-SiH4-H2 mixture, because of the H2 dilution and the presence of SiF4, favours the amorphous - crystalline transition through the etching process of the amorphous phase. The x - ray diffraction measurements give an average grain size of about 100 Å. The presence of these nanocrystals shifts the absorption edge of the films towards higher energy. An energy gap of 2.12 eV is estimated, although the hydrogen content in the material is only 4.5 at. %. The temperature dependence of the photoluminescence behaves similarly to that of porous silicon.

The infrared absorption in doped microcrystalline silicon thin films is analyzed by modelling the complex permittivity as the sum of the contributions resulting from interband transitions and from absorption by charge carriers. Their density and the drift mobility within grains is described by free carrier motion according to the Drude theory. However, for a good fit to experimental data a small trapping energy, reflecting the effect of grain boundaries, is included in the model. By comparing results obtained from the analysis of infrared data with conductivity and Hall measurements in films grown in a very high frequency (VHF) plasma and by hot-wire chemical vapor deposition (CVD), we show that infrared transmission measurements provide a simple access to transport parameters in these films.

The spin-lattice relaxation times (T1) of conduction electron (CE) and dangling bond (DB) centers in μc-Si:H have been directly measured using the 3-pulse inversion recovery method. For both CE and DB, the inversion recovery curve follows a stretched exponential form. T1 of DB is about twice the T1 of CE, however the temperature dependence of T1 seems to be the same for both CE and DB and can be approximated by T−4 While the DB echo decay is modulated by both 29Si and 1H nuclei, we found no modulation of the CE echo decay by the H nucleus, indicating that CE centers are located in H-depleted phases in μc-Si:H. The modulation results are direct evidence that CE centers are located in the crystalline grains and DB centers in the amorphous phases.

To get information on the density of states distribution and the photocarrier recombination in microcrystalline silicon (μc-Si:H), samples with various amounts of n- and p-type doping are studied with electron spin resonance (ESR) and stationary and time-resolved light induced ESR. The intensity of the dark ESR signals from dangling bonds (DB) and conduction electrons (CESR) is investigated as a function of the doping level. The DB signal has a flat distribution over a wide doping range while the CESR signal strongly increases with n-type doping. Upon illumination with white or infrared light both resonances are enhanced with an intensity that depends on the doping level. The decay of the light induced signal and the dependence in time and intensity of the residual signal on different initial excitation energies and dark/light -sequences is studied. The results are discussed with a schematic band diagram for μc-Si:H. The existence of a potential barrier is proposed which spatially separates photogenerated carriers. A large band-offset between crystalline and disordered regions is further suggested.

Hall-effect experiments on <n>-type microcrystalline silicon samples with a wide range of structural composition and doping have been performed. For highly doped samples the conductivity Σ and the mobility μ show a non-singly activated behaviour while the carrier density is almost temperature independent. The comparison of the carrier density with the phosphorous concentration in conjunction with the conductivity gives strong evidence that the Hall-effect data have to be corrected with the crystalline volume fraction Xc. Furthermore, the increase of the mobility with Xc, which is linked in our case to the grain size, can be explained when the length of the transport paths is taken into account. Our results will be discussed in the framework of different transport models. It is concluded that transport in μc-Si:H can not be explained in terms of thermionic emission over barriers with a well defined barrier height; instead a distribution of barrier heights have to be considered. A transport model is suggested where μc-Si:H is viewed as an interconnected network.

Melting and rapid solidification has been induced in DC-sputtered amorphous Ge (a-Ge) films on glass substrates by irradiation with picosecond laser pulses at 583 nm. The melting-solidification kinetics has been followed by means of real time reflectivity measurements with ns resolution and the structure of the rapidly solidified material has been analyzed by means of Raman spectroscopy in micro-Raman configuration. The results obtained show that for laser pulse fluences above a certain threshold recalescence occurs during solidification leading to the formation of nanocrystalline Ge embedded in an amorphous matrix. The phonon correlation length (L) obtained from the Raman spectra of the irradiated regions has been used to analyze the evolution of the crystallite size with the laser fluence. For low fluences above the recalescence threshold, the values of L are in the 8–10 nm range. However, if the fluence is sufficiently increased, the crystallite size shows a clear linear dependence on the fluence with phonon correlation lengths scaling from 6 to 13 nm.

The electrical characteristics of multilayer structures based on amorphous ultrathin diamondlike carbon films were investigated including dynamic and quasi-static current-voltage characteristics, capacitance-voltage characteristics, deep level transient spectra. The effect of illumination and temperature on these characteristics was also investigated. For the multilayer structures composed of lower band gap amorphous carbon layers separated with higher band gap ones, there were observed well-defined regions of negative differential resistance and sharp 20-fold changes in capacitance at definite voltages. Activation energies, capture cross sections, and locations of trapping centers were defined. The effects observed are discussed in terms of trap-assisted tunneling and, also, in terms of resonant tunneling between energy levels in superlattices and charge filling of the quantum wells and trapping centers.

Indium tin oxide (ITO) semiconductive films were deposited by an atmospheric RF plasma technique. Indium-to-tin (In:Sn) ratios varied from 10:0 to 0:10. A small amount of antimony was doped into some ITO samples for comparative studies. Substrate materials were soda-lime-silicate (SLS) float glass and fused silica glass. Structural, electrical, and optical properties were dependent on the In:Sn ratio, precursor material feeding rate, oxygen feeding rate, and other deposition conditions.

Micro Raman spectra for PbZrxTi1-xO3 (PZT) with a grain size of 60 nm have been recorded. The results show that the lowest E(TO) phonon mode of PbTiO3 (soft mode) displays a decrease in frequency and increase in linewidth with increasing Zr concentration. A discontinuous behavior of the phonon energy of the soft mode occurs at x=0.4 and it can be attributed to a phase transformation from the tetragonal ferroelectric to rhombohedral ferroelectric phase in PZT. The coupling between the soft mode and an additional impurity mode, has been observed, which plays an important role in the phase transformation. A lowest phonon mode at 10 cm−1 is detected and it is found to exhibit an increase in intensity for x above 0.2. The grain size dependence of the mode seems to be associated with the effect of grain size on the microstructure in PZT. The mechanism of grain size - induced new morphotropic phase boundary, which is lower than that of the corresponding bulk materials, is discussed.

In the past, microcrystalline silicon (μc-Si:H) has been successfully used as active semiconductor in entirely μc-Si:H p-i-n solar cells and a new type of tandem solar cell, called the “micromorph” cell, was introduced [1]. Micromorph cells consist of an amorphous silicon top cell and a microcrystalline bottom cell. In the paper a micromorph cell with a stable efficiency of 10.7 % (confirmed by ISE Freiburg) is reported.

Among sofar existing crystalline silicon-based solar cell manufacturing techniques, the application of microcrystalline silicon is a new promising way towards implementing thin-film silicon solar cells with a low temperature deposition. Microcrystalline silicon can, indeed, be deposited at temperatures as low as 220°C; hence, the way is here open to use cheap substrates as, e.g. plastic or glass. In the present paper, the development of single and tandem cells containing microcrystalline silicon is reviewed. As stated in previous publications, microcrystalline silicon technique has at present a severe drawback that has yet to be overcome: Its deposition rate for solar-grade material is about 2Å/s; in a more recent case 4.3 Å/s [2] could be obtained. In the present paper, using suitable mixtures of silane, hydrogen and argon, deposition rates of 9.4 Å/s are presented. Thereby the dominating plasma mechanism and the basic properties of resulting layers are described in detail. A first entirely microcrystalline cell deposited at 8.7 Å/s has an efficiency of 3.15%.

The first successful deposition of ‘micromorph’ silicon tandem solar cells of the n-i-p-n-i-p configuration is reported. In order to implement the ‘micromorph’ solar cell concept, four key elements had to be prepared: First, the deposition of mid-gap, intrinsic microcrystalline silicon (μc-Si:H) by the 'gas purifier method', second, the amorphous silicon (a-Si:H) n-i-p single junction solar cell, third, the microcrystalline silicon n-i-p single junction solar cell and fourth, the ability of depositing on aluminium sheet substrates.

All the solar cells presented have been deposited on flat aluminium sheets, using a single layer antireflection coating to couple the light into the cell. It is shown, that this antireflection concept- together with a flat substrate- holds for amorphous single junction solar cells, but it reaches its limit with the extended range of spectral response of the ‘micromorph’ cell.

The best initial efficiencies for each category of n-i-p cells on flat substrates were: 8.7% for the amorphous silicon single junction cell, 4.9% for the microcrystalline silicon single junction cell and 9.25% for the ‘micromorph’ tandem cell.

A 7.7 % single junction cell efficiency for an entirely microcrystalline silicon (μc-SiH) device has recently been reported by our group [1]. This was achieved by applying the purifier technique, a technique which is indeed easier to handle than the earlier used “microdoping” approach. The purpose of the present paper is twofold: First to show in detail the impact on device performance when a gas purifier is used; and second to illustrate that the deposition rate of the active, absorbing i-layer can be increased from the former 1.55 Å/s up to 4.3 Å/s while still maintaining reasonable device performances. In the latter case a first n-i-p solar cell structure on an aluminium sheet could be fabricated with an efficiency of 4.9 %.

The <p> μc-SiC:H / <i> a-Si:H junction can be considered to be a sub-system of a n/i/p solar cell. Optimised performance of this junction can be assumed to be a key feature for obtaining high efficiency solar cells.

In this paper the authors present results on the conductivity of boron doped microcrystalline hydrogenated silicon (<p> μc-Si:H) thin films deposited on amorphous substrates (e.g. glass or glass/<i> a-Si:H). It is shown that, without any treatment of the substrate or of the underlying surface, the <p> layers showed a strongly reduced conductivity. This indicates either a bad nucleation or a poor microcrystalline behaviour. By using an appropriate surface treatment of the substrate, a gain in photoconductivity of about three orders of magnitude could be obtained (σ > 3 S/cm at a layer thickness of 400Å). We conclude from this, that for thin <p> type μc-Si:H layers the nucleation conditions are essential for obtaining best electric properties of the film w.r.t. solar cell performance.

Based on these results, interface treatment was successfully implemented in n/i/p solar cells deposited on TCO coated glass and stainless steel. The results of these experiments are also presented.

We have applied real time spectroellipsometry (RTSE) to study the growth of microcrystalline silicon n- and p-layers [μc-Si:H:(P,B)] incorporated into amorphous silicon (a-Si:H) p-i-n and n-i-p solar cells, respectively. In previous research, we have applied RTSE to characterize a-Si:H solar cells having only amorphous component layers. The μc-Si:H(P,B) component layers, however, pose a more difficult RTSE analysis problem for two reasons. First, the near-surface of the underlying i-layer is modified in the μc-Si:H:(P,B) growth process, and second, the microstructural evolution near the i/(n,p) interfaces is very complicated. From RTSE spectra (1.5 < hv < 4 eV) collected every ∼4–15 s during growth, we have extracted the time evolution of the μc-Si:H:(P,B) layer microstructure, thicknesses, and optical properties along with the modifications that the near-surface i-layer properties undergo in the formation of the i/(n,p) interfaces. We suggest that the beneficial optical properties of the microcrystalline layers may be due to size effects in the crystallites that make up the films.

A microwave remote plasma system, operating in an electron cyclotron resonance (ECR) condition, has been designed to deposit microcrystalline silicon (μ c-Si). The plasma properties have been studied by Langmuir probe measurements in the deposition region. Microcrystalline silicon films of thickness < 0.3 μm have been grown by the decomposition of 2% SiH4/Ar diluted in H2. The films were analyzed for dark and photoconductivity, crystallinity and total H2 content. Raman spectroscopy indicates >50% crystallinity for films deposited between 300–400 °C at pressures of 10 mTorr with an input power in the range of 200–600 W for a H2/SiH4 ratio of 60. An increase in deposition temperature from 300 to 400 °C resulted in an increase in conductivity along with a decrease in the activation energy. H2 evolution studies indicate that the purely μ c-Si films show a total 2.5% H2 content compared with the 16.5% seen for the totally amorphous films. Better structural and electrical properties have more recently been obtained using 2% SiH4/He mixtures.

Phosphorous (P) doped hydrogenated microcrystallme silicon (n+μ c-Si:H) films have been prepared by using the hydrogen-diluted plasma enhanced chemical vapor deposition (PECVD) method. The crystallinity of films deposited over the range of SiH4/H2 flow ratios and RF-power is studied by Raman spectroscopy. For a 900 Å thick film deposited at 250°C, a conductivity of 71Ω−1cm−1 and an average crystallinity of 49% is obtained. n+ μ c-Si:H films as well as n+ a-Si:H films are used for both etch stopper and back channel etch type TFTs and the I4-V8 characteristics are compared. For the etch stopper type TFT, the field effect mobility of 0.85 cm2/V.sec, threshold voltages of 2 – 3 V and Ion/Ioff ratio of ∼107 are obtained.

This paper reports technological experiments which have strongly affected the properties of the multilayer image sensor structure. The high deposition rate and large hydrogen content during the reactive magnetron deposition process causes nanocrystallization of prepared silicon films. We also report experiments with laser crystallization. The effect of microstructure in a-Si:H films on TFT and pin diode characteristics has been investigated. Crystallinity was confirmed by Raman scattering, small angle X-ray diffraction (SAXD) and transmission electron microscopy (TEM). The parameters of the photodiodes such as quantum efficiency, dark and light currents, etc. have been tested using the measurements of samples in the configuration of a linear image sensor consisting of two rows, 30 to 160 pixels per row, with dimensions 0.1mm2-1mm2.