Structural and surface characterization of large diameter, crystalline AlN substrates for device fabrication

In order to meet the need for higher quality nitride substrates, 2 in diameter boules of AlN have been developed and, from them, 2 in diameter substrates have been prepared with high crystalline quality. Double-crystal X-ray rocking curves indicate a full-width at half-maximum (FWHM) of 65 and 83 in on the symmetric (0 0 0 2) and the asymmetric (1 0 1¯ 4) lines, respectively. Etch pit density (EPD) measurements of dislocations are consistent with ∼103 cm−2 in the substrate. EPD measurements after homoepitaxial growth are typically ∼104 cm−2. Growth of AlxGa1−xN layers will increase the number of threading dislocations but graded buffer layers have been used to produce GaN layers with EPD of order 105 cm−2.