Nitridation behavior of sapphire using a carbon-saturated N2–CO gas mixture

Abstract

The authors previously developed a sapphire nitridation method using carbon-saturated N2–CO gas mixture to form a high-quality AlN film for III-nitride-based optoelectronic devices. In this study, the nitridation behavior of (0001) (c) plane and (112¯0) (a) plane sapphire was studied to elucidate and optimize the process at temperatures of 1823 and 1873 K. The AlN film thickness, surface morphology, crystal quality, and interfacial phenomena were investigated as functions of nitridation time and temperature. Fundamentally, the AlN film grows as a result of the diffusion process that occurs in the AlN film. The voids found at the AlN/sapphire interface indicate that the Al2O3 dissociates into Al3+ and O2− ions, and that the ions diffuse in the AlN film. However, the growth rate of AlN film does not obey the simple diffusion model. The AlN film thickness has a maximum and decreases slightly with time, which indicates that the thermal decomposition of AlN film must be considered when comprehensively describing the nitridation process.

Annealing of an AlN buffer layer in N2–CO for growth of a high-quality AlN film on sapphire

“…Annealing condition of AlN buffer on sapphire using N 2 -CO gas mixture. 14) Annealing temperature atomic steps were observed on its surface. However, the surface of the AlN buffer layer with t Buf = 1000 nm was rough even after annealing.…”

Influence of substrate temperature on the crystalline quality of AlN layers deposited by RF reactive magnetron sputtering

“…All of the AlN sputtered layers were grown on nitrided sapphire substrates with a diameter of 50.8 mm (2 inches) prepared using a reported sapphire nitridation method. 15,16 The crystalline quality of the nitrided sapphire substrate is described in section 3.5. Before sputtering, the nitrided sapphire substrates were ultrasonically cleaned in acetone and ethanol for 15 min each.…”

“…The TEM sample was prepared using a focused ion beam method. Two types of g/3g weak-beam dark-field TEM images taken near the AlN [11][12][13][14][15][16][17][18][19][20] zone axis with g = [10-10] and [0002] were obtained to determine the type of dislocation in the AlN sputtered layer. Here, g is a reciprocal lattice vector of the diffraction plane.…”

“…Selected area electron diffraction patterns and pole figures demonstrated that the nitrided sapphire layer was a single-crystalline AlN film. 15,16 Using this nitrided sapphire as a template, homoepitaxial growth of AlN layers can be attained by reactive sputtering.…”

“…13,14 The AlN sputtered layers were grown on nitrided sapphire substrates prepared using a sapphire nitridation method. 15,16 The nitrided sapphire substrates allowed formation of high-quality AlN layers with a thickness of about 10 nm on the c-plane sapphire surface. FWHM-XRCs of AlN (0002) and (10-10) on the nitrided sapphire substrates were less than 100 and 1000 arcsec, respectively.…”