Hydrothermal liquid phase epitaxy of gallium orthophosphate on quartz crystal substrates

Gallium orthophosphate (GaPO 4 ) layers for surface acoustic wave (SAW) and sensor applications have been grown on quartz crystal substrates with sizes of about 30 x 30 mm 2 by hydrothermal liquid phase epitaxy (HLPE). The growth of epitaxial GaPO 4 layers is difficult because of a strong tendency for twinning. Besides, a retrograde solubility and an intense chemical aggressiveness of the solution has to be considered. Nevertheless, we found an effective crystal growth technique to deal with these problems using large and qualitatively good substrate crystals of quartz. The most important step of the epitaxy is the formation of an interlayer between the quartz substrate and the GaPO 4 deposit. Epitaxial layers with thickness up to 500 μm were obtained and characterised by means of X-ray techniques.