Measurement of the ionisation and attachment coefficients in monosilane and disilane

The ionisation alpha /p 0 , electron attachment eta /p 0 and effective ionisation alpha /p 0 (= alpha /p 0 - eta /p 0 ) coefficients for monosilane (SiH 4 ) and disilane (Si 2 H 6 ) were measured by the steady-state Townsend method for 60<E/p 0 <270 V cm -1 Torr -1 , where E is the electric field and p 0 is the gas pressure reduced to 0 degrees C. The results show that the values of alpha /p 0 and alpha /p 0 for SiH 4 and Si 2 H 6 are smaller than that of CH 4 , and the value of alpha /p 0 for Si 2 H 6 is about 1 / 3 of that for SiH 4 . The value of eta /p 0 is found smaller than about 5*10 -2 cm -1 Torr -1 for the E/p 0 values studied here. It appears that the present work is the first to report the value of these parameters. The limiting E/p 0 , at which alpha /p 0 = eta /p 0 , for SiH 4 and Si 2 H 6 , is determined to be about 65 and 125 V cm -1 Torr -1 , respectively. The total secondary ionisation coefficient gamma T for these gases are also measured for E/p 0 >150 V cm -1 Torr -1 and found to be less than 10 -5 .