The role played by different types of threading dislocations ͑TDs͒ on the electrical properties of AlGaN/GaN heterostructure grown by plasma-assisted molecular beam epitaxy ͑MBE͒ was investigated. Samples with different defect structures and densities were prepared and measurements were taken from the same sample to study the correlative behavior of various TDs. From the Hall measurement, the electron mobility in two-dimensional electron gas channel was mainly controlled by the edge dislocation, which has a dominant amount in the material. The edge TDs acted as Coulomb scattering centers inside the channel and reduces the carrier mobility and increased its resistance. Screw TDs played a much significant role than edge TDs in determining the reverse-bias leakage current of Schottky barrier diodes. Leakage current is affected slightly by the reduction of free carrier density in the channel for samples with a higher edge TD density, but screw TD, which acted as the current leakage path, was more deleterious to the reverse-bias leakage current of AlGaN/GaN structure.

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High quality GaN film was successfully grown on 150 mm Si ͑111͒ substrate by metal-organic vapor phase epitaxy method using AlN multilayer combined with graded AlGaN layer as buffer. The buffer layer structure, film quality, and film thickness are critical for the growth of the crack-free GaN film on Si ͑111͒ substrate. Using multilayer AlN films grown at different temperatures combined with graded Al 1−x Ga x N film as the buffer, the tensile stress on the buffer layer was reduced and the compressive stress on the GaN film was increased. As a result, high quality 0.5 m crack-free GaN epitaxial layer was successfully grown on 6 in. Si substrate.

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In this paper, we present the effect of multiple thin high-low-high-temperature AlN (HLHT AlN) nucleation layers on GaN film quality. A 1.9-µm-thick GaN film grown on Si (111) substrate shows that the multiple HLHT AlN nucleation layers have a significant effect on GaN film quality. This process also plays a very important role in the growth of GaN films on Si (111) substrates. A high quality GaN film with a uniformly faceted surface with very low dislocation densities is obtained at the optimized multiple HLHT AlN nucleation layers 50-nm thick at a temperature of 1010-800-1010°C and a growth pressure of 50 Torr.