Large-area AlN substrates for electronic applications: An industrial perspective

We report on the status of the vapor growth of high-quality AlN bulk crystals by the sublimation-recondensation technique for the commercial production of AlN wafers up to 2 in diameter. AlN boules and wafers have been characterized by X-ray Laue backscattering, diffraction, and rocking curves measured in double-axis configuration, demonstrating a full-width at half-maximum (FWHM) of 28 and 32 arcsec for the symmetric and asymmetric rocking curves, respectively. The etch pit density (EPD) for different AlN substrate orientations was found to be less than 104 cm(-2). Impurity levels have been measured by glow discharge mass-spectrometry (GDMS) and secondary ion mass-spectroscopy (SIMS). The oxygen content as measured by SIMS shows concentrations < 10 cm. Additionally, a high thermal conductivity of similar to 270 W/mK has been measured by the flash method. High-quality homoepitaxial and graded AlGaN layers were grown on the on-axis-oriented AlN substrates. The lack of both piezoelectric and spontaneous polarization fields, for nitride heterostructures grown in non-polar directions, has recently created significant interest in high-quality, non-polar nitride Substrates to boost the performance of light emitting diodes (LEDs) and laser diodes. Initial epitaxial results on non-polar AlN substrates are presented. (c) 2008 Elsevier B.V. All rights reserved.