Deep-uv Transparent Bulk Single-crystalline Aln Substrates

Bulk aluminium nitride (AlN) is a very promising substrate material for UV optoelectronics based on AlGaN ternary compounds. AlN single crystals exceeding 1'' in diameter can now be grown by physical vapour transport (PVT). UV transparency is of high interest for UV devices designed to emit through the substrate. We report on 500 μm thick bulk AlN substrates with plain UV transmittance of 50% (i.e., absorption coefficients < 15 cm) at wavelengths down to 220 nm in almost the whole wafer area. Results from optical absorption (OA) are correlated to the structural quality of the samples and compared to cathodoluminescence (CL) measurements and chemical analysis.