Large aluminum nitride crystals with reduced defects and methods of making them

A method of growing single-crystal AlN, the method comprising:

• providing in a crystal growth enclosure a vapor comprising Al and N2;
• and
• depositing the vapor as single-crystalline AlN while pushing the crystal growth enclosure at a rate less than an intrinsic growth rate of the single-crystalline AlN, the single-crystalline AlN having at least one of (i) an optical absorption coefficient of less than 5 cm−1 at all wavelengths in a range spanning 500 nm to 3,000 nm or (ii) an optical absorption coefficient of less than 1 cm−1 at any wavelength in a range spanning 210 nm to 4,500 nm.

The method of claim 1, wherein the crystal growth enclosure comprises at least one of tantalum and carbon, and a growth temperature is less than approximately 2750° C.

The method of claim 1, wherein a temperature gradient of greater than approximately 5° C./cm and less than approximately 100° C./cm is maintained along a length of the crystal growth enclosure while depositing the vapor.