Liquid target pulsed laser deposition and its applications to growing diamond/diamondlike carbon and gallium nitride thin films

A novel liquid-target pulsed laser deposition (LTPLD) technique has been developed. The technique has overcome the problem of solid target deterioration under high power laser irradiation and has prevented large particulates on the growing film. The LTPLD is simple and safe to operate and the cost of source materials is much lower than that in chemical vapor depositions. Choosing an organic liquid containing carbon and hydrogen as a target material, we have obtained crystalline diamond film in the presence of reactive gases H2O2/O2. The film, as revealed by atomic force microscopy, raman spectroscopy, and x-ray diffraction, is composed of cube-shaped diamond crystals with most of them aligned in 220 directions. The results give some evidence that hydroxyl ions, together with atomic oxygen can indeed promote diamond formation. Since gallium is a melt above 29.8 degrees C, it is an ideal material system for LTPLD. Using ammonia as a nitrogen supplier we have succeeded in obtaining gallium nitride thin films at low deposition temperatures. By choosing an appropriate buffer layer we have grown c-axis oriented wurtzite gallium nitride films on several kinds of substrates including fused silica. With addition of indium into gallium target, InGaN films can also be prepared by LTPLD.