Irradiation of High Energy Electrons onto GaN Thin Films and Observation of Induced Optical Luminescence in Inductively-Coupled Plasmas

This paper reports observation of optical fluorescence of GaN thin films in an inductively-coupled plasmas containing energetic electrons with an energy higher than several keV. Such high energy electrons are produced by sheath acceleration of secondary electrons induced by ion bombardment at a negatively-biased electrode. A current of a Langmuir probe located in such a plasma is investigated to examine how the high energy electrons behaves in the plasma. It was found that a step-like increment of probe current observed immediately after the negative high voltage application was proportional to discharge power, but slightly depended on the pulse target voltage. A sample of undoped GaN film was observed to emit significant optical fluorescence in the wavelength range of 370-390 nm corresponding to band gap energy of the GaN when the plasma contains the high energy electrons, the fluorescence intensity of the GaN film increased with the incident electron energy higher than a critical energy of $\sim $5 keV. These results suggested cathode luminescence technique will be used to detect a damage density of GaN substrate surface even in plasma environment.