Wet etching and infrared absorption of AlN bulk single crystals

The defects and the lattice perfection of an AlN(0001) single crystal grown by the physical vapor trans-port(PVT) method were investigated by wet etching, X-ray diffraction(XRD), and infrared absorption, respectively.A regular hexagonal etch pit density(EPD) of about 4000 cm-2 is observed on the(0001) Al surface of an AlN single crystal.The EPD exhibits a line array along the slip direction of the wurtzite structure, indicating a quite large thermal stress born by the crystal in the growth process.The XRD full width at half maximum(FWHM) of the single crystal is 35 arcsec, suggesting a good lattice perfection.Pronounced infrared absorption peaks are observed at wave numbers of 1790, 1850, 2000, and 3000 cm-1, respectively.These absorptions might relate to impurities O, C, Si and their complexes in AlN single crystals.