Thin film Si solar cell has been developed using Via-hole Etching for the Separation of Thin films(VEST) process. The process is based on SOI technology of zone-melting recrystallization (ZMR) followed by chemical vapor deposition (CVD), separation of thin film, and screen printing. Key points for achieving high efficiency are (1)quality of Si films, (2)back surface emitter (BSE), (3)front surface emitter etch-back process, (4)back surface field (BSF) layer thickness and its resistivity, and (5)defect passivation by hydrogen implantation. As a result of experiments, we have achieved 16% efficiency(Voc:0.589V, Jsc:35.6mA/cm2, F.E:0.763) with a cell size of 95.8cm2 and the thickness of 77μm. It is the highest efficiency ever reported for large area thin film Si solar cells.

Silicon films of thicknesses (100 – 800 nm) are deposited on Si[111] substrate at 490°C using Si+ ions of energies (20 – 70 eV) from Silane plasma. The structure of the films depends on the energy of Si+ ions and the film grows epitaxially for ion energy <20 eV. Si films are analyzed by X-ray diffraction technique.

We have investigated the surface morphology of thick SiGe layers grown on Si(100) substrates. SiGe layers containing different Ge concentrations (from 0 to 16 at.%) and having thickness of about 15μm are prepared by liquid phase epitaxy (LPE) method using various growth conditions. The wavelength of undulation of SiGe layers is found to be increasing when we adopt low cooling rates during LPE process. The roughness of the layer does not show any significant change with cooling rate.

In this paper we present results for the absorption coefficient and refractive index spectra of p-and n-type silicon membranes doped with phosphorous or boron at different levels. These results cover the wide energy range from 0.5 eV up to 2.5 eV, thus including effects of subgap defect and impurity absorption, and the range of possible transitions to higher conduction band minima. The results have been obtained by utilizing both a conventional transmission and reflection measurement technique at small values of transmittance, and a recently developed optical interference spectroscopy characterization technique. The results in the visible and near infrared regions from the two techniques have been compared, and the range of transmission where the conventional technique is applicable have been determined. The preliminary analysis of these data indicate that a new information regarding the Si electronic band structure can be extracted.

Plasma deposition of thin silicon films with a variable microstructure and controlled interface formation techniques are being developed for thin film silicon/polycrystalline silicon solar cells. Low hydrogen content amorphous (a-Si) or microcrystalline silicon (μ c-Si) films were obtained by controlling the H2 dilution of 2% SiH4/He in a microwave ECR discharge. The films were characterized for structural and electro-optic properties. Junction creation for solar cells was investigated by depositing single or multilayers of the film silicon onto crystalline silicon (c-Si). Effort to improve carrier transport and photovoltaic (PV) properties was pursued through interface modifications effected by varying the microstructure of the layer in contact with the substrate. Cells with 7% conversion efficiency (No A/R) were obtained for an a-Si/c-Si heterojunction configuration. Improved carrier transport and PV properties (9% ef ficient) were achieved by inserting a thin μ c-Si layer in the above structure.

A new silicon deposition reactor fabricated in our laboratory is presented in this paper. It works at Sub-Atmospherical total pressure, so it is a SAPCVD reactor. The deposition rates and electronic transport properties are compared with a conventional LPCVD reactor.

In order to study their applicability as the active base material in Si thin crystalline film solar cell technology, SiGe relaxed layers grown by Liquid Phase Epitaxy (LPE) and Chemical Vapor Deposition (CVD) on Si substrates are investigated by optical and electrical measurements (TEM, EXD, PL, EBIC). The main results of this work is to point out the improvement of the SiGe active base layer by using smooth Ge graded SiGe buffer layer and remote plasma hydrogenation. TEM, EXD, PL experiments show the effect of the Ge graded buffer layer grown using LPE, by confining the threading dislocations in the SiGe buffer layer close to the Si/SiGe interface. EBIC measurements reveal low recombination activity of dislocations at 300 K providing the diffusion length exceeds the 15 μm layer thickness The enhanced luminescence of SiGe near bandgap indicates that remote plasma hydrogenation induces a decrease of the non-radiative recombination pathways due to dislocations on CVD layers where defect recombinations dominate as indicated by EBIC measurements.

This study points out the importance of controlling relaxed SiGe layers with good minority carrier recombination quality as a key issue for the optimization of new SiGe/Si based solar cells.

Thin layers made of densely packed silicon nanocrystals sandwiched between amorphous silicon dioxide layers have been manufactured and characterized. An amorphous silicon/amorphous silicon dioxide superlattice is first grown by CVD or RF sputtering. The a-Si layers are recrystallized in a two-step procedure (nucleation + growth) to form layers of nearly identical nanocrystals whose diameter is given by the initial a-Si layer thickness. The recrystallization is monitored using a variety of techniques, including TEM, X-Ray, Raman, and luminescence spectroscopies. When the a-Si layer thickness decreases (from 25 nm to 2.5 nm) or the a-SiO2 layer thickness increases (from 1.5 nm to 6 nm), the recrystallization temperature increases dramatically compared to that of a single a-Si film. The removal of the a-Si tissue present between the nanocrystals, the passivation of the nanocrystals, and their doping are discussed.

The preliminary results of the effects of the Si beam irradiation for the Si surface preparation on the growth of GaAs on Si by MBE are reported. The effects are combined with thermal cyclic anneal (TCA). A slight improvement in the crystalline quality is observed on the photoluminescence spectra of the films grown with Si irradiation. In our experimental conditions, Si irradiation during the Si surface preparation has not indicated large effects on the FWHM of XRD. It is also indicated that initial substrate surface treatment affects the quality of thicker film through TCA treatment. Higher substrate temperature during Si beam irradiation is expected to indicate positive Si beam irradiation effects.

With a selective nucleation and solid phase epitaxy (SNSPE) process, grain sizes of 10 μm have been achieved to date at 620°C in 100 nrm thick silicon films on amorphous SiO2, with potential for greater grain sizes. Selective nucleation occurs via a thin film reaction between a patterned array of 20 rnm thick indium islands which act as heterogeneous nucleation sites on the amorphous silicon starting material. Crystal growth proceeds by lateral solid phase epitaxy from the nucleation sites, during the incubation time for random nucleation. The largest achievable grain size by SNSPE is thus approximately the product of the incubation time and the solid phase epitaxy rate. Electronic dopants, such as B, P, and Al, are found to enhance the solid phase epitaxy rate and affect the nucleation rate.

Poly-Si films were deposited at temperatures as low as 325°C by a newly proposed method. In the proposed method, both Ni-enhanced crystallization effects and vapor-phase deposition were utilized to reduce the deposition temperature. The X-ray diffraction measurement shows that the films were (110)-oriented at temperatures among 325°C to 419°C. When the partial pressure of hydrogen gas in the deposition chamber exceeds 0.1%, crystallization was disrupted. The characteristics of TFTs and pn junction diodes showed its potential applicability to AMLCDs and sollar cells.

Oxidation of porous silicon has been studied using thermal activity monitoring, i.e. isothermal microcalorimeter. It was found that, at room temperature (25 °C) the micro-calorimetric signal from the oxidation of the p+-type porous silicon (PS) reduces exponentially, while in the case of n-type PS, the signal starts to increase slowly, reaching its highest value after some hours. This kind of behaviour is typical of autocatalytic reactions. To clarify the origin of the difference, we varied the preparation parameters of the porous silicon. We determined the activation energy from the measurements near the room temperature (25–70 °C). The results of this research have been compared with the previous observations and the possible origin of the difference has been discussed.

Crystalline silicon films have been deposited on silicon and metal-coated coming 7095 glass substrates at temperatures of 280 ˜ 680°C by electron cyclotron resonance (ECR) plasma assisted chemical vapor deposition (PACVD) using an ultrahigh vacuum chamber and SiH4 as the feedstock. X-ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) have been used to characterize the films. At temperatures of ˜280 °C, the as-grown films are microcrystalline with crystalline fractions between 50–97%. From XRD patterns, randomly oriented crystalline silicon grains were clearly present in the films with the grain sizes estimated to be between 170 – 370Å. As the growth temperature is increased to 470°C, epitaxial growth on silicon is observed at growth rates of 240Å/min without bias or hydrogen plasma treatment before film growth. N-type doping of the layers has been achieved using PH3 as the doping gas and solar cells with ECR grown emitters fabricated on 15μm thick p-type epilayers on p+ substrates.

In this paper, a method to obtain by CVD Si layers on silicon oxide with the desired grain size is described, involving nucleation control through the growth parameters. Nucleation experiments are carried out with a hydrogen - dichlorosilane - HCl ambient at high temperature. The nucleus density is observed to drop to low values at a threshold HCl-flow. A qualitative explanation using concepts from atomistic nucleation theory is proposed. The effect of addition of diborane to the gas flow is investigated and appears to be small or non-existent . Finally, preliminary results of a thin-film crystalline silicon solar cell process applied on such layers are given to illustrate the potential of such layers.

A new technique for making large-grain thin Si films is described in which optical excitation is used to enhance the grain growth. Grain sizes much larger than the film thickness can be obtained at low temperatures and in short process times. This method is well suited for making thin-film Si solar cells on low-temperature substrates.

We present a new device structure for a high efficiency, thin-film, silicon solar cell. A preliminary design and an approach for fabrication of such a cell are discussed. The cell structure uses interface texturing and a back surface reflector for effective light trapping. A theoretical analysis is applied to determine the major parameters of the cell. These analyses indicate that a cell efficiency of about 18% is attainable with a Si film thickness of 10–15 μm, and grain size of about 50 μm. A method for making a large-grain thin cell is proposed.

A systematic atomic-scale analysis is presented of the interactions of chemically reactive radicals originating in silane/hydrogen discharges with surfaces of hydrogenated amorphous silicon (a-Si:H) films. The hydrogen concentration on the surface is identified as the major factor that controls both the reactivity of the radicals and the surface reaction mechanism; other important factors include the location of impingement of the radical on the surface and the molecular orientation of the radical with respect to the surface. SiH is found to react with a-Si:H surfaces independent of location of impingement and radical orientation; the reaction mechanism, however, depends strongly on the hydrogen coverage of the surface and impingement location. Our results are in excellent agreement with experimental data for the reaction probability of SiH with a-Si:H film surfaces.

The crystalline structure, Electron Paramagnetic Resonance and Surface Photovoltage (SPV) spectra of C60 thin films and the photovoltaic properties of C60/Ag and C60/Si interfaces are reported. The SPV spectra of C60 films, C60/Ag and C60/Si interfaces are presented and analyzed on the basis of a model of C60 film electron structure including mobility gap, band tails extending into the gap and two deep level states in the gap. I-V characteristics of the C60/Ag and the C60/P-Si interfaces were measured. Both device structures are shown to exhibit rectifying behavior in the dark and photovoltaic properties. The solar cell parameters are presented.

In this paper we describe our research efforts directed towards the understanding of the CdS/CuInGaSe2junctions and, specifically, the interaction of the chemical bath with the CuInGaSe2 (CIGS). We find that Cd and S diffuse into the absorber during the CdS growth. Heating the absorbers in Cd partial baths resuled in a significant improvement in the ZnO/CIGS device properties. Photoluminescence measurements indicate that the effect of Cd is very similar to that of CBD CdS.

How stable are Cu(In,Ga)Se2 solar cells? CuInSe2 is known also as an ionic Cu conductor and the Cu-In-Se system has a rich phase diagram. Two stability-related problems are treated from a thermodynamic point of view: -a- Cu migration, -b- phase segregation. We show how Cu migration imparts self-stabilization on the system. Based on recently reported results on the room temperature phase diagram of CuInSe2, we explain why an overlayer of an ordered vacancy compound (OVC) is not to be expected to appear as a separate phase, even though the surface composition corresponds to that of the I-III3V5 OVC compound.