Ba Bas Korevaar

Hydrogenated amorphous silicon deposited at very high growth rates by an expanding Ar–H2–SiH4 plasma

The properties of hydrogenated amorphous silicon (a-Si:H) deposited at very high growth rates (6–80 nm/s) by means of a remote Ar–H2–SiH4 plasma have been investigated as a function of the H2 flow in the Ar–H2 operated plasma source. Both the structural and optoelectronic properties of the films improve with increasing H2 flow, and a-Si:H suitable for the application in solar cells has been obtained at deposition rates of 10 nm/s for high H2 flows and a substrate temperature of 400 °C. The “optimized” material has a hole drift mobility which is about a factor of 10 higher than for standard a-Si:H. The electron drift mobility, however, is slightly lower than for standard a-Si:H. Furthermore, preliminary results on solar cells with intrinsic a-Si:H deposited at 7 nm/s are presented. Relating the film properties to the SiH4 dissociation reactions reveals that optimum film quality is obtained for conditions where H from the plasma source governs SiH4 dissociation and where SiH3 contributes dominantly to film ...

High hole drift mobility in a-Si:H deposited at high growth rates for solar cell application

Time-of-flight measurements on hydrogenated amorphous silicon deposited with a remote expanding thermal plasma at growth rates up to 12 nm/s have revealed a 7 to 10 times larger hole mobility than for films deposited with conventional rf-PECVD. The electron mobility on the other hand is up to 3 times less. Based on a determination of the density of states by post-transit photo-current analysis we suggest a comparable defect density at mid-gap as for films deposited with rf-PECVD. These material properties have been obtained at a substrate temperature of 400°C, which is needed to obtain solar grade material at these growth rates. Possible causes of these particular material properties, which may have application in thin film solar cells, are discussed. Furthermore we show that the high substrate temperature is still a drawback in solar cell preparation when using the standard p-i-n configuration.

Fast deposition of microcrystalline silicon with an expanding thermal plasma

Abstract Microcrystalline silicon has been deposited using an expanding thermal plasma. High deposition rates are achieved, which is attractive for solar cell production. A first survey of the influence of the deposition parameters on the optical, electrical and structural material properties is performed. SEM analyses show columnar growth and infrared absorption shows varying oxygen content. For some of the deposition conditions the dark and photoconductivities approximate 10−7 and 10−5 S/cm, respectively. Also the deposition plasma has been studied by means of mass spectrometry. It is concluded that the expanding thermal plasma is well suited for the deposition of microcrystalline silicon at growth rates up to 3.7 nm/s.

Integration of expanding thermal plasma deposited hydrogenated amorphous silicon in solar cells

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The role of H in the growth mechanism of PECVD a-Si:H

This paper describes an extension of the silyl radical based kinetic growth model by atomic hydrogen induced surface hydrogen abstraction processes. It is shown that by including this direct abstraction process several problems of the SiH 3 based model are resolved. The defect density can be predicted with the proper temperature dependence and order of magnitude. The implications for high rate deposition of a-Si:H are discussed

Argon-surface interactions in ibad-deposited molybdenum films

Argon incorporation and defect creation were studied experimentally. Direct desorption measurements have been used to establish the argon implantation profile. A projected range and range straggle of 0.8 and 3.5 A were found. Argon is incorporated at substitutional positions. The creation rate of defects by argon was studied by helium desorption spectrometry. A net creation rate of (0.7 ± 0.4) × 10 −3 vacancy/argon atom was found. Ion assisted deposition at elevated substrate temperatures shows that all incorporated argon acts as helium trap. Argon fluence variations show an effective cross-section for self sputtering of 31 A 2 , a trapping probability of 6.5%, and a maximum achievable argon concentration of 4 × 10 −3

Electron paramagnetic resonance as a probe of technologically relevant processing effects on CdTe solar cell materials

The performance of polycrystalline thin film CdTe solar cells is limited by as yet poorly understood deep level defects which serve as recombination centers. Electron paramagnetic resonance (EPR) has unrivaled analytical power and sensitivity in the identification of deep level defects in semiconductors; however, very little EPR literature exists with regard to technologically relevant processing of present day polycrystalline CdTe solar cells. In this study we explore the effects of several features important in these present day processing techniques: (1) effects of CdCl2 etching and (2) effects of Cu on the CdTe. Cu is widely used with CdTe solar cells and is thought to play a significant role in CdTe solar cells performance. Although the EPR spectra in all the cases we explored are dominated by a substitutional Mn site signal, our results are clearly sensitive to multiple changes caused by the aforementioned processing parameters.

High-rate microcrystalline silicon for solar cells

In order to produce thin silicon films for solar cells at high growth rates we deposited films with a cascaded arc expanding thermal plasma. We demonstrate the power of this technique by applying amorphous films deposited at rates up to 1.4 nm/s in solar cells. We used the same deposition technique to produce microcrystalline silicon films. Growth rates up to 3.7 nm/s are achieved. The material structure is analyzed using Raman spectroscopy and XRD. We see that the crystalline fraction increases with the H/sub 2/ flow, whereas the amorphous and the void fraction decrease.

Temperature dependence at various intrinsic a-Si:H growth rates of p-i-n deposited solar cells

With a cascaded arc expanding thermal plasma, intrinsic solar grade amorphous silicon can be deposited at growth rates varying from 2 to 100 /spl Aring//s. The temperature above which good material is obtained becomes higher for higher growth rates. Higher deposition temperatures affect the p-layer within p-i-n grown solar cells, which will result in other optimum deposition temperatures of the i-layer. In this paper, the authors address the dependence of the p-i-n solar cell performance on the deposition rate and deposition temperature.