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 wit h a remote expanding thermal plasma at growth rates up to 12 nm/s have reve aled a 7 to 10 times larger hole mobility than for films deposited with con ventional rf-PECVD. The electron mobility on the other hand is up to 3 time s less. Based on a determination of the density of states by post-transit p hoto-current analysis we suggest a comparable defect density at mid-gap as for films deposited with rf-PECVD. These material properties have been obta ined at a substrate temperature of 400 degrees C, which is needed to obtain solar grade material at these growth rates. Possible causes of these parti cular material properties, which may have application in thin film solar ce lls, 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. (C) 2000 Elsevier Science B.V. All rights reserved.