Mar 5, 2014

Growth of GaN epilayers on c-, m-, a-, and (20.1)-plane GaN bulk substrates obtained by ammonothermal method

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 50 mbar. 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.
GaN substrates of various crystallographic orientations were obtained by ammonothermal method.
► GaN epilayers were grown on c-, m-, a-, and (20.1)-plane GaN substrates by MOCVD.
► Influence of substrate polishing on the quality of GaN epilayers has been demonstrated.
► MOCVD growth conditions have been optimized for m-plane GaN epilayers.
► Optical and structural properties have been compared for c-, m-, a-, and (20.1)-plane GaN epilayers.

Source: Journal of Crystal Growth

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