Other deep-UV-emitting semiconductors exist in addition to the gallium and aluminum nitrides (and combinations thereof) that form the basis for all common blue- and UV-emitting semiconductor lasers and light-emitting diodes. For example, hexagonal boron nitride (hBN) emits in the 200 nm range. The best performance occurs for single crystals, which emit an intense line at 215 nm when optically pumped. However, fabrication of these crystals has traditionally required high pressure and high temperature (HP-HT) in a closed barium-BN system.
Scientists at the National Institute for Materials Science (Tsukuba, Ibaraki, Japan) have developed a way to synthesize high-quality hBN crystals under atmospheric pressure by using a nickel-molybdenum-based substrate that also served as the solvent. The solvent and hBN powder were heated to 1500°C and cooled, producing multiple hBN crystals, typically 10 µm thick and as large as 200 × 300 µm in size. The resulting plate of crystals was 9 × 4 mm in size. When compared to a HP-HT-fabricated hBN crystal, the new crystal exhibited the same strong, narrow peak at 215 nm. The researchers were also able to grow hBN crystals on sapphire substrates. Contact Yoichi Kubota at [email protected].