THIS PROJECT IS AIMED TO PROVIDE IMPROVED ALLOY MATERIAL FOR AMORPHOUS SILICON CELLS WITH P-I-N STRUCTURE. IT WILL FOCUS ON THE DEVELOPMENT OF NEW WAYS TO OBTAIN SIC:H(F) AND SIGE:H(F) ALLOYS WITH IMPROVED ELECTRICAL AND OPTICAL PROPERTIES. FOR THIS PURPOSE NEW GASEOUS PRECURSOR COMPOUNDS FOR THE PLASMA AND THERMAL CHEMICAL VAPOUR DEPOSITION OF AMORPHOUS SILICON CONTAINING CARBON AND/OR GERMANIUM WILL BE SYNTHESIZED AND TESTED UNDER A VARIETY OF EXPERIMENTAL CONDITIONS. REPLACEMENT OF CONVENTIONAL CARRIER GASES, LIKE SIH4, CH4, GEF4, OR GEH4, BY MOLECULES OF MIXED STOICHIOMETRY SHOULD LEAD TO PRODUCTS OF SUPERIOR PHOTOVOLTAIC PROPERTIES. IN COLLABORATION WITH INDUSTRIAL LABORATORIES THE CELLS WILL BE OPTIMIZED TO GIVE HIGHER EFFICIENCY AND PERFORMANCE.
Hydrogenated amorphous silicon carbide compounds have attracted research interest in recent years owing to their use in a wide range of electronic applications (such as solar cells, photoreceptors and other photoelectronic units). Recent investigations have shown that the optoelectronic properties of amorphous silicon carbon hydrogen compounds depend on the nature of incorporation of the carbon atoms into an amorphous framework. A new approach to obtaining layers with an improved efficiency is directed towards the application of volatile organosilanes that have few or no carbon hydrogen bonds as chemical vapour deposition (CVD) feedstock.
In a systematic study a large family of small, simple, ternary compounds (silicon carbon hydrogen) of high volatility showed great promise as starting materials for CVD. These included polysilylmethane, methylsilane, disilylmethane, trisilylmethane and tetrasilylmethane. In addition, the use of germanium powder results in the conversion of silanes to germanes. Owing to their high volatility they have the potential to produce amorphous germanium carbon hydrogen compounds or amorphous germanium silicon carbon hydrogen materials.
These compounds offer a number of advantages including safe handling, cheapness and commercial availability of components, and high thermal stability. Investigations have been undertaken into new methods for the production of CVD compounds. For example a new preparative strategy was tested successfully for the production of trisilylmethane. Used in CVD, trisillylmethane improved the photoelectrical quality of the amorphous films.
THIS PROJECT IS ORIENTED TOWARDS THE PREPARATION OF IMPROVED ALLOY MATERIALS FOR AMORPHOUS SILICON CELLS FROM NEW FEEDING GASES. SINCE THE INITIAL RESULTS OBTAINED WITH SILYMETHANES (H3SI)N CH4-N HAVE BEEN VERY ENCOURAGING (IN PARTICULAR REGARDING USAGE OF THE SPECIES WITH N = 2 AND 3), THE PREPARATIVE METHODS FOR THE SYNTHESIS OF THESE COMPOUNDS HAVE BEEN IMPROVED FURTHER THROUGH THE DEVELOPMENT OF OTHER SYNTHETIC ROUTES. IT HAS BEEN FOUND THAT A THREE-STEP PROCEDURE STARTING FROM PHENYLCHLOROSILANE/SILICHLOROFORM, WITH PHENYL-SILYL- AND BROMOSILYL-METHANES AS THE INTERMEDIATES, GIVES BETTER YIELDS AND A HIGH PURITY PRODUCT N = 3 IN REPRODUCIBLE EXPERIMENTS. THE CRYSTAL STRUCTURES OF THE PHENYLATED INTERMEDIATED HAVE BEEN DETERMINED BY X-RAY DIFFRACTION, AND THE GASES (DSM, TSM) HAVE BEEN CHARACTERIZED BY ANALYTICAL AND SPECTROSCOPIC MEASUREMENTS, INCLUDING INFRARED AND PHOTOELECTRON SYUDIES.
PHOTOVOLTAIC PROPERTIES OF AMORPHOUS FILMS OF HYDROGENATED SILICON/CARBON ALLOYS OBTAINED IN CONVENTIONAL PLASMA CVD EXPERIMENTS WITH DISILYLMETHANE/SILANE MIXTURES ARE SUPERIOR TO FILMS GENERATED FROM SILANE/METHANE MIXTURES UNDER STANDARD CONDITIONS. THE RESULTS CAN BE INTERPRETED ON THE BASIS OF A MODIFIED STRUCTURE AS SHOWN BY A SERIES OF ANALYTICAL INVESTIGATIONS. EXPERIMENTS USING MICROWAVE-GENERATED ATOMIC HYDROGEN ARE ALSO IN PROGRESS. STUDIES WITH A-SI/GE:H AND A-GE/C:H MATERIALS WILL FOLLOW.