Fabrication of native, single-crystal AlN substrates

Aluminum nitride (AlN) is a promising substrate material for emerging wide-bandgap electronic and opto-electronic devices. Although existing manufacturing technology is less mature than for sapphire and silicon carbide substrates, aluminum nitride has been demonstrated to be superior for deep UV lightemitting applications and may ultimately surpass silicon carbide in both cost and performance for high power RF. Advantages include the identical crystal structure and close lattice match to high Al-content nitride alloys. In addition, AlN and GaN have closely matched thermal expansions from room temperature up to typical growth temperatures. The AlN has a band-gap energy of 6.2 eV with an index of refraction of 2.2 which is attractive for the extraction of uv light and is highly insulating which is attractive for high frequency devices. We use a sublimation-recondensation approach to produce large bulk AlN single crystals. Single crystal boules 15 mm in diameter and several cm in length have been grown and native-nitride substrates with dislocation densities below 10³ cm^-2 and with a thermal conductivity exceeding 3 W/cm-K at 300K, have been obtained from those boules. Crystal IS is currently developing 50 mm diameter single-crystal boules.