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Direct and fast growth of a SI:GAAS thin film by means of thermionic vacuum arc (TVA)

The thermionic vacuum arc (TVA) plasma is an electrical discharge fired between a hot filament as cathode and a material to be evaporated as anode of a plasma diode. The main characteristic of the TVA is it ignites in the anode material vapors continuously generated by bombardment with electrons emitted by the filament and accelerated towards anode in a vacuum chamber, which is depressurized down to a residual pressure less than 10-5 Torr. Due to the very low pressure in the chamber but high vaporization rate of the hot anode a rather large gradient of the concentration anode material vapors is produced. This gradient can explain plasma formation in the anode region where vapor pressure is large enough to assure electron-atom collisions and ionizations so that anodic plasma may appear. On the other hand, very low pressure in the rest of the chamber allows the atoms to move freely, deposit and condensate on any surface placed in the chamber. Consequently, the TVA is a very suitable technique for deposition of high purity thin films. Moreover, due to the low pressure the ions generated within the anode plasma are accelerated towards the chamber wall and move almost without collisions and bombard the layer produced by condensation of the anodic material vapors. This bombardment of a growing film by energetic particles strongly influences the growth mechanisms and the structure of the film leading to a more compact structure and low roughness of the deposited thin layer.