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The work shows a successful fabrication of AlGaN/GaN high electron mobility transistor (HEMT) structures on the bulk GaN substrate grown by ammonothermal method providing an ultralow dislocation density of 104 cm−2 and wafers of size up to 2 inches in diameter. The AlGaN layers grown by metalorganic chemical vapor phase epitaxy method demonstrate atomically smooth surface, flat interfaces with reproduced low dislocation density as in the substrate. The test electronic devices—Schottky diodes and transistors—were designed without surface passivation and were successfully fabricated using mask-less laser-based photolithography procedures. The Schottky barrier devices demonstrate exceptionally low reverse currents smaller by a few orders of magnitude in comparison to the Schottky diodes made of AlGaN/GaN HEMT on sapphire substrate. [ABSTRACT FROM AUTHOR]

GaN/AlGaN quantum wells (QWs) were grown by metal–organic vapor phase epitaxy (MOVPE) on c -, a -, m -, and (20.1)-plane GaN substrates obtained by the ammonothermal method in the same MOVPE process, i.e. a process with growth parameters optimized for c -plane GaN templates. The structural properties of GaN/AlGaN QWs were carefully investigated by high angle annular dark field scanning transmission electron microscopy. Sharp GaN/AlGaN interfaces were seen for QWs grown on the c -, a -, and m -plane GaN substrates, but very rough interfaces with {1-100} and {1-101} facets were observed on the (20.1)-plane GaN substrate. In addition, the Al-rich region of AlGaN and GaN transition was identified for each of the GaN/AlGaN QW samples deposited in this process. The thickness and composition of this region varied with the crystallographic orientation of GaN substrates. [ABSTRACT FROM AUTHOR]

Abstract: GaN epilayers were grown by metalorganic chemical vapor deposition (MOCVD) on c-, m-, a-, and (20.1)-plane GaN substrates obtained by the ammonothermal method. The influence of (i) the surface preparation of substrates, (ii) MOCVD growth parameters, and (iii) the crystallographic orientation of substrates on the structural and optical properties of GaN epilayers was investigated and carefully analyzed. It was observed that the polishing of substrates and their misorientation have strong impact on the quality of GaN epilayers grown on these substrates. The MOCVD growth process was optimized for epilayers grown on m-plane GaN substrates. The best structural and optical properties were achieved for epilayers deposited at 1075°C and the total reactor pressure of 50mbar. These conditions were applied to grow GaN epilayers on substrates with other (c-, a-, and (20.1)-plane) crystallographic orientations in the same MOCVD process. Particularly good optical properties were obtained for GaN epilayers deposited on polar and non-polar (m- and a-plane) substrates, whereas slightly worse optical properties were observed for epilayers deposited on the semi-polar substrate. It therefore means that MOCVD growth conditions optimized for a given crystallographic direction (m-plane direction in this case) work rather well also for other crystallographic directions. [Copyright &y& Elsevier]