THE DOPING EFFICIENCY OF BORON IN SILICON SOLAR CELLS IS LIMITED BY THE PRESENCE OF OXYGEN WHICH FORMS A COMPLEX WITH BORON.

THE DOPING EFFICIENCY OF BORON IN SILICON SOLAR CELLS IS LIMITED BY THE PRESENCE OF OXYGEN WHICH FORMS A COMPLEX WITH BORON. SPECIFICALLY, THE INTERSTITIAL BORON-INTERSTITIAL OXYGEN DEFECT STRUCTURE IS CREATED WHEN THE BORON CONCENTRATION IS IN THE RANGE OF 5 X 10 14 TO 2 X 10 16 ATOMS/CM3 IN CONJUNCTION WITH AN OXYGEN CONCENTRATION OF 4 X 10 16 TO 3 X 10 17 ATOMS/ CM3. THE MAXIMUM DEFECT CONCENTRATION REPORTED BY DREVINSKY AND DE ANGELIS IS 4 X 10 13 ATOMS/CM3 WHICH INDICATED THAT ONLY ONE IN A THOUSAND OXYGEN ATOMS WILL COMPLEX WITH BORON. THE INTERSTITIAL BORON-INTERSTITIAL OXYGEN MINORITY CARRIER TRAP CAN NOT BE ELIMINATED UNLESS ALL THE INTERSTITIAL OXYGEN ATOMS ARE REMOVED OR TRAPPED. HEAT TREATMENT AT 650 DEGREES TO 800 DEGREES CELSIUS FOR 20 HOURS OR 1000 DEGREES CELSIUS FOR 20 HOURS WILL PRODUCE OXYGEN AGGLOMERATES THAT WILL TRAP INTERSTITIAL OXYGEN ATOMS. THIS REDUCES THE NUMBER OF INTERSTITIAL OXYGEN ATOMS WHICH WOULD BE AVAILABLE TO COMPLEX WITH BORON. THE ADVANTAGE OF THIS TECHNIQUE IS THAT NO IMPURITIES HAVE BEEN ADDED TO THE SILICON THAT COULD REDUCE THE EFFICIENCY OF THE SOLAR CELL. MOST OTHER HEAT-TREATMENT PROCEDURES COULD BE USED SUB- SEQUENTLY IN PROCESSING THE SOLAR CELL AND NOT DESTROY THE INERT OXYGEN COMPLEX. THE NEWLY CREATED OXYGEN COMPLEX IS VERY STABLE; ONLY HEAT TREATMENT AT 1350 DEGREES CELSIUS WOULD CAUSE DISASSOCIATION.