Free-standing gallium nitride (GaN) substrates are in high demand for power devices, laser diodes, and high-power light emitting diodes (LEDs). SixPoint Materials Inc. has begun producing 2” GaN substrates through our proprietary Near Equilibrium AmmonoThermal (NEAT) growth technology. In a single 90 day growth, eleven c-plane GaN boules were grown from free-standing hydride vapor phase epitaxy (HVPE) GaN substrates. The boules had an average X-ray rocking curve full width at half maximum (FWHM) of 33 ± 4 in the 002 reflection and 44 ± 6 in the 201 reflection using 0.3 mm divergence slits. The boules had an average radius of curvature of 10.16 ± 3.63 m. The quality of the boules was highly correlated to the quality of the seeds. A PIN diode grown at Georgia Tech on a NEAT GaN substrate had an ideality factor of 2.08, a high breakdown voltage of 1430 V, and Baliga’s Figure of Merit of >9.2 GW/cm2. These initial results demonstrate the suitability of using NEAT GaN substrates for high-quality MOCVD growth and fabrication of high-power vertical GaN switching devices.
This paper reports two inch gallium nitride (GaN) substrates fabricated from bulk GaN crystals grown in the near equilibrium ammonothermal method. 2″ GaN wafers sliced from bulk GaN crystals have a full width half maximum of the 002 X-ray rocking curve of 50 arcsec or less, a dislocation density of mid-10 5 cm −2 or less, and an electron density of about 2 × 10 19 cm −3 . The high electron density is attributed to an oxygen impurity in the crystal. Through extensive surface preparation, the Ga surface of the wafer shows an atomic step structure. Additionally, removal of subsurface damage was confirmed with grazing angle X-ray rocking curve measurements from the 114 diffraction. High-power p-n diode structures were grown with metalorganic chemical vapor deposition. The fabricated devices showed a breakdown voltage of over 1200 V with sufficiently low series resistance.
X-ray topography measurements on a 100 mm diameter GaN boule grown by the Near Equilibrium AmmonoThermal (NEAT) method revealed an improvement in dislocation density from >1 x 106 cm-2 to between 2 × 105 and 5 × 105 cm-2, an improvement greater than two to five times from seed to growth. This data builds on previous x-ray diffraction and defect selective etching to quantify the reduction in defect density that is closely associated with increasing growth thickness. This result indicates that there is a pathway to further dislocation reduction by increasing growth thickness for GaN crystals including those of 100 mm or larger diameter. Further reduction of the dislocation density of large-area substrates will lead to GaN power devices with reduced leakage current under reverse bias and better device performance.
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