Crystalline silicon thin film solar cells on glass substrates are a low cost alternative to silicon wafer cells. As an alternative to a simple furnace annealing step in which a-Si is converted to c-Si with 1 µm grains, an epitaxial crystal growth process is presented here. First a seed layer is prepared on glass by diode laser crystallization of an a-Si layer on glass to result in 100 µm grains. Then a-Si is deposited on top of the seed which is converted to c-Si by epitaxial growth. A 1.1 µm thick c-Si layer with 100 µm grains was produced in this way. The paper presents details of the epitaxial growth process.

The fabrication of silicon nanowire-based solar cells on silicon wafers and on multicrystalline silicon thin films on glass is described. The nanowires show a strong broadband optical absorption, which makes them an interesting candidate to serve as an absorber in solar cells. The operation of a solar cell is demonstrated with n-doped nanowires grown on a p-doped silicon wafer. From a partially illuminated area of 0.6 cm(2) open-circuit voltages in the range of 230-280 mV and a short- circuit current density of 2 mA cm(-2) were obtained.

Multicrystalline silicon thin film solar cells with a grain size of about 100 /spl mu/m were prepared on a borosilicate glass substrate by the LLC (Layered Laser Crystallization) process. This process consists of depositing a-Si by PECVD, crystallizing a highly p-doped seed layer by scanning the beam of a cw laser, and epitaxially thickening the seed by further depositing a-Si and applying pulses of an excimer laser periodically during deposition. Doping profiles for absorber and emitter are introduced by adding diborane or phosphine during PECVD. The seed acts as a transparent electrode. Solar cells 2 /spl mu/m thick show a V/sub oc/ of 545 mV, a fill factor of up to 71%, and an efficiency of 3.3%.

In a one chamber process multicrystalline silicon thin film solar cells with crystallites in the range of 10 to more than 100 pm were deposited on uncoated glass by Layered Laser Crystallization (LLC). During PECVD deposition of a-Si:H, laser crystallization was performed in the deposition chamber. A 400 nm thick seed layer simultaneously acting as transparent electrode was crystallized by scanning an Ar+-laser beam. Epitaxial thickening by applying repeated pulses of an KrF excimer laser was performed during further a-Si:H deposition. p(+)-p-n(+) cells with 3 mum thick absorber without. reflector and without antireflection coating showed V-OC = 425 mV, I-SC = 9.8 mA/cm(2), FF = 55%, and n = 2.3%.

Layered laser crystallization during PECVD of a-Si:H is a new and advantageous method to deposit c-Si films onto glass with a rate of 10 Angstrom s(-1). This new technology consists of two laser-induced crystal growth steps: A seed layer is prepared from a-Si:H by an overlapped scanning of an Ar+ laser beam. Then the seed is repeatedly thickened by melting of newly deposited a-Si:H on top of the c-Si with KrF laser pulses. Various deposition parameters were matched together to process a layer with crystallites 100 mum in size. p(+)pn(+)- or n(+)np(+)-junctions were deposited in one chamber and in one run. V-OC of 530 mV was achieved. (C) 2002 Elsevier Science B.V. All rights reserved.

A technology is proposed to prepare crystalline silicon thin film solar cells on glass as a superstrate. In a first step an a-Si:H layer is deposited by PECVD onto borosilicate glass. By scanning an Ar/sup +/-laser beam, this layer is crystallized with grains several 10 /spl mu/m in size and is at the same time p/sup +/-doped by boron from the glass so that a transparent electrode layer is formed. In the next step further a-Si is deposited and repeatedly irradiated by an excimer laser during deposition. In this way, a p-absorber layer is grown epitaxially from the underlying electrode which is acting as a seed layer. Finally, by excimer laser doping, a n/sup +/-emitter is fabricated to result in a p/sup +/-p-n/sup +/-layer sequence. Onto the silicon, a metal is deposited as the second electrode acting as a back reflector. Results on the characterization of the different layers are presented with the emphasis on crystallographic and chemical properties. Challenges in preparing the proposed layer sequence are discussed.

By melting amorphous silicon layers on glass by the beam of an Ar+ laser, large grained polycrystalline films as well as single crystalline regions at predefined positions were generated.If the layers are crystallized by scanning a circular laser beam at a rate of up to 5 cm/s the crystal size depends on the overlap between successive scanning traces. The lateral dimensions of the crystals exceed several 10 mu m for an overlap slightly above 50%. Crystals with size dimensions of about 100 mu m were produced by line scanning of a focused laser beam.Large single crystals were obtained by scanning a sickle-shaped or L-shaped beam profile. If the laser is switched on and off repeatedly, single crystalline regions are produced at predefined positions. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

During RF CVD of a-Si:H onto glass an Ar+ laser beam was scanned to crystallize a seed layer. Subsequently every 20 nm new deposited a-Si:H was molten by one light pulse from a KrF laser, so that the laser processing did not take any additional time. A highly conducting p(+) region close to the glass as transparent electrode and a p(+)pn junction within the film were deposited without a doping gas. REM, TEM images and XRD measurements confirmed an epitaxial growth of large crystallites. The self structured silicon/glass interface and film surface show increased scattering which supports light absorption. Transients of open circuit voltage after a pulsed generation by UV light at the p(+), as well as at the n side, were contactless sensed to evaluate the PV quality of films as deposited. A lifetime of more than 5 mus and a diffusion length for holes of more than 25 mum were determined.

Conditions for crystallizing a-Si:H films on glass substrates by laser methods are discussed. Special emphasis is given to crystallization procedures for thin film solar cells and for TFT's using Ar(+) or Cu vapor lasers. The properties of the resulting films such as grain structure, electrical properties, and impurity concentration is discussed.

Polycrystalline silicon thin film solar cells require coarse grained silicon layers on a glass substrate. The preparation starts with a layer of amorphous silicon some hundred nanometers thick. By laser crystallization it is converted into a seed layer consisting of grains several ten μm in size. We report on in situ diagnostics by time resolved reflection and transmission (TRRT) measurements during the preparation process. Joint diagnostics by different lasers and the comparison with optical and electron micrographs of the resulting films give unique information about the crystallization processes. Even if different processes occur in hydrogenated or hydrogen free amorphous silicon films during the heating induced by different irradiation parameters the results of crystallization are quite similar.

For polycrystalline silicon thin film solar cells a silicon layer 50 μm thick is required consisting of grains 100 μm in diameter deposited on low cost glass substrate. We report on a preparation method combining plasma enhanced CVD of amorphous silicon and laser crystallization. We start from a-Si:H thin films 200 nm thick which are deposited on glass (Corning 7059) by a rf-CVD process. These films are irradiated by scanning with an Ar+ laser to result in crystals of several 10 μm in diameter. In order to increase the film thickness on this crystalline seed layer further amorphous silicon is deposited by the same CVD process at a rate of 20 nm/min. During the deposition the growing layer is irradiated by excimer laser pulses with about 300 mJ/cm2 at a repetition rate of less than 0.1 Hz. Each laser pulse melts the newly deposited amorphous layer down to the crystalline interface which acts as a homoepitactic substrate during resolidification. In this way the whole growing amorphous layer is converted to a polycrystal.

This paper deals with experimental investigations of the effect of a rotating magnetic field on a diffusion cooled CO 2 laser discharge. Some properties relevant to laser activity are discussed, e.g. neutral gas temperature, magnetically driven gas rotation, pumping rate, and distribution of small signal gain within the discharge tube. By means of an intracavity method the radial distribution and the time behavior of the laser output power were measured.

This paper deals with some investigations of the gas discharge and the optical properties of a transverse flow cw CO2-laser in the output power range of 5 kW. The optical qualities of the generated laser beam depend very sensitively on the type and design of the optical resonator. Different unstable optical resonators and optical inhomogenities of the transversely excited active medium will be discussed. Experimental results (laser output power, beam cross sections, focal spot) will be presented.

This paper deals with investigations of the spatial structure of the electrical potential, the current density, the gas temperature and the reduced electrical field strength in the discharge volume of a transverse gas flow CO 2 -laser in dependence on the geometry of the electrodes. The data were obtained by means of Langmuir double probes. The results are compared with optical measurements applying a probe laser resonator.

This paper deals with investigations of the spatial structure of the electrical potential, the current density, the gas temperature and the reduced electrical field strength in the discharge volume of a transverse gas flow CO2-laser in dependence on the geometry of the electrodes. The data were obtained by means bf Langmuir double probes. The results are compared with optical measurements applying a probe laser resonator. A calculation of the laser output power of a transverse flow laser is carried out on the base of rate equations including the convective losses. The position of the laser cavity in the gas flow direction is discussed to find optimum conditions.

The evolution from regular to fully irregular motion of the s′ variety of an ionization wave in neon is studied by space correlation measurements. The correlation functions clearly indicate the onset of strongly nonlinear interaction (by a change in the decay constant of correlation function) in the region of coherent wave motion, the transition to irregular wave motion (short distance correlation only) and the stochastic character of fully developed irregular wave motion (correlation only over a few wavelengths and a few periods).

The elementary theory of ionization waves, given by Pekárek, is modified to include the influence of a magnetic field. The resulting dispersion ralation delivers an interpretation of the wave phenomena in argon low-pressure low-current columns under the influence of a local transversal field. The suppresion of ionization waves by weak magnetic fields as well as the excitation of wave-packet-like fluctuations in the case of strong magnetic fields can be shown.