Phosphorus effusion cell for molecular beam epitaxy

An evacuated phosphorus effusion cell capable of outputting a phosphorus vapor stream and comprising:

• a) a red phosphorus sublimation chamber heatable to a first temperature to generate said phosphorus vapor stream;
• b) a flux valve to control said outputting of said phosphorus vapor stream;
• and
• c) cooling means to cool said phosphorus vapor stream downstream of said sublimation chamber;
• wherein said flux control valve is located to be subject to cooling from said cooling means.

A phosphorus effusion cell for producing a flow of phosphorus vapor regulated by a valve, said phosphorus effusion cell comprising:

• a) a vessel for sublimation of red phosphorus to phosphorus vapor to said flow of phosphorus vapor;
• and
• b) a vacuum-tight valve closing said vessel and openable to output said phosphorus vapor flow, said valve regulating said phosphorus vapor flow;
• wherein said vessel has two zones, said zones being independently thermostatted to different temperatures and comprising a hot zone for sublimation of red phosphorus to produce phosphorus vapor and a cold zone for condensation of white phosphorus from said phosphorus vapor and re-evaporation of said white phosphorus;
• and wherein said cold zone is located downstream from said hot zone and upstream from said vacuum-tight valve, whereby phosphorus can flow from said hot zone to said vacuum-tight valve via said cold zone.