Structural and Electrical Characterization of 2” Ammonothermal Free-Standing GaN Wafers. Progress toward Pilot Production

Abstract

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.

Flow Stability, Convective Heat Transfer and Chemical Reactions in Ammonothermal Autoclaves—Insights by In Situ Measurements of Fluid Temperatures

“…The concentration of the mineralizer is denoted as c min , whereas c GaN,dissolved refers to the dissolved amount of GaN based on gravimetric evaluation. 1 The given density of ammonia refers to the density of the supercritical fluid and was determined based on the initial fill volume and fill density. 2 Experimental data based on [21] and references therein.…”

“…The ammonothermal method has evolved as a particularly promising route for the synthesis of major quantities of high-quality bulk GaN crystals. Several groups have demonstrated two-inch crystal diameters or even larger crystals [1][2][3][4], growth rates of several hundreds of micrometers per 2 of 18 day [3][4][5] and nearly bow-free crystals with a radius of curvature exceeding 1000 m [4,6]. In addition, the method has proven to be a valuable tool for exploratory syntheses of nitride materials [7,8] including earth-abundant semiconductors [9,10].…”

Numerical Simulation of Ammonothermal Crystal Growth of GaN—Current State, Challenges, and Prospects

“…The ammonothermal method has initially been developed as a tool for the synthesis and recrystallization of metal amides and metal nitrides, taking advantage of enhanced solubilities of inorganic substances in supercritical ammonia containing mineralizers [1]. Starting from 1995 [2], the ammonothermal process has been increasingly researched as a method for the growth of GaN bulk crystals [3][4][5][6][7][8]. Depending on the choice of mineralizer, it is possible to obtain GaN in its cubic or wurtzite structure [9], although most research has focused on wurtzite GaN.…”

“…Depending on the choice of mineralizer, it is possible to obtain GaN in its cubic or wurtzite structure [9], although most research has focused on wurtzite GaN. The ammonothermal method is recognized as particularly promising for the growth of GaN with high structural quality by using near-equilibrium conditions [6,10]. On the contrary, impurity concentration and thus conductivity control are particularly challenging due to the closed growth system [11].…”

“…Due to its scalability, the ammonothermal method is still believed to have the potential to become a strong competitor for halide vapor phase epitaxy (HVPE), which is the most common method for bulk GaN growth at present [13]. Recent progress in ammonothermal GaN growth includes a demonstration of scalability to pilot production for simultaneous growth of likely about 100 boules in one reactor [6], a masking technique for circumventing issues related to growth on different facets [18], growth of nearly bowfree crystals (radius of curvature: 1460 m) at pressures as low as 100 to 120 MPa [19], and growth of nearly 4-inch size crystals while keeping off-angle distributions as small as ±0.006 • along both a-axis and m-axis [20]. Besides its use for the growth of bulk GaN, the ammonothermal technique is increasingly being utilized for exploratory syntheses of various binary, ternary, and multinary nitride and oxynitride materials [21][22][23], including nitride semiconductors composed of earth-abundant elements [24].…”