Ammonothermal bulk GaN substrates for LEDs

Soraa has developed a novel ammonothermal approach for growth of high quality, true bulk GaN crystals at a greatly reduced cost. Soraa’s patented approach, known as SCoRA (Scalable Compact Rapid Ammonothermal) utilizes internal heating to circumvent the material-property limitations of conventional ammonothermal reactors. The SCoRA reactor has capability for temperatures and pressures greater than 650 °C and 500 MPa, respectively, enabling higher growth rates than conventional ammonothermal techniques, yet is less expensive and more scalable than conventional autoclaves fabricated from nickel-based superalloys. SCoRA GaN growth has been performed on c-plane and m-plane seed crystals with diameters between 5 mm and 2" to thicknesses of 0.5-4 mm. The highest growth rates are greater than 40 μm/h and rates in the 10-30 μm/h range are routinely observed. These values are significantly larger than those achieved by conventional ammonothermal GaN growth and are sufficient for a cost-effective manufacturing process. Two-inch diameter, crack-free, free-standing, n-type bulk GaN crystals have been grown. The crystals have been characterized by a range of techniques, including x-ray diffraction rocking-curve (XRC) analysis, optical microscopy, cathodoluminescence (CL), optical spectroscopy, and capacitance-voltage measurements. The crystallinity of the grown crystals is very good, with FWHM values of 15-80 arc-sec and average dislocation densities below 5 x 10 5 cm -2 .