Formation of gallium nitride (G[lc]aN) crystals by plasma bombardment

Abstract

GaN crystals were directly grown on liquid Ga surface immersed in a nitrogen plasma. The surface of liquid Ga suspended on a sputtering target turned from shiny and metallic to dark and opaque in color when negative bias voltage was applied to the target. As the opaque crust layer was formed on the top surface of the target, the ion saturation current to the target and the intensity of the line spectrum radiation from Ga decreased. Langmuir probe analysis also showed that the incoming N2 ion flux decreased when the crust was formed. By continuous bombardment of N2 ions on the negatively-biased Ga target polycrystalline and textured GaN crystals were formed. The crystals appeared rough on the top and bottom surfaces but showed partly shiny and well faceted appearance in the inner part of the bulk crystal when cleaved. The surface morphology of the bulk GaN crystals was analyzed using scanning electron microscope (SEM). X-ray diffraction peaks confirmed the irradiated materials to be fine crystalline GaN with distinct primary reflection which indicated good texturing of the formed crystal. The observed angle corresponded to (002) reflection of hexagonal GaN, or (111) reflection of cubic GaN. Optical spectrum of the light emitted from the shiny portion of the inner bulk crystal was obtained by injecting a He-Cd laser light. The emitted light from the crystal exhibited a broad spectrum showing its peak at 350 nm (3.54 eV).