7.1 Development of a Compact NH_3 Jet - Introduction
The realization that sufficient particle fluxes for reasonable GaN growth
rates are unattainable with the original jet motivated the development
of a compact NH_3 jet located in one of the source flanges. The only feasible
pumping solution in the region between the nozzle and skimmer is by the
use of a cryoshroud since it can be placed directly inside that region.
Other types of pumps can only be connected through a network of ducts reducing
the effective pumping speed xi to values far below the needed pumping
speed to maintain a low enough background pressure P_b.
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