or channel densities may be easily interchanged fig2 depicts the calculated flux distribution for a single 50 u00d7 300 u03bcm channel as a function of source to substrate distance using a maximum backing pressure of 10 1 torr curve 30 represents a source to substrate distance of 0 5 cm curve 32 represents a distance of 1 0 cm curve 34 represents a distance of 2 0 cm and curve 36 represents a distance of 5 0 cm the microchannel plate array assembly has been incorporated into a gsmbe chamber used to grow silicon the enhancement of growth rate realized by using the source has been demonstrated table i below lists two experiments performed with identical substrate temperatures and gas flow conditions but differing source to sample distances a significant increase in growth rate is observed with decreasing source to substrate distance consistent with the beam characteristics of the microchannel plate as illustrated in fig2 table i______________________________________growth rate of si from sih sub 4 as a functionof microchannel plate to substrate distance x substrate t sih sub 4 flow x growth rate u00b0 c sccm cm u03bcm hr ______________________________________700 50 1 3 1 6700 50 6 3 0 6______________________________________ the volume of the microchannel plate assembly of the invention is significantly smaller than that of a conventional gas source cell this permits mounting of the microchannel plate assembly on an internal translation device to allow variation of the distance between the microchannel plate and the.