Orientation control of non- and semi-polar GaN using directional AlN sputtering on(10-10) Sapphire

摘要

Directional sputtering has been developed at Nagoya University to realize (10-13) GaN and (10-15) GaNoriented layers on (001) Si substrates, although FWHM in X-ray diffraction (XRD) were rather broad andthickness on Si is quite limited. The proposed mechanism was shadowing during the directional sputtering.The (10-13) GaN orientation has the lowest lattice mismatch to the sapphire surface unit cell for [0001]Al2O3|| [11-20]GaN. Hence, we used (10-10) sapphire as a substrate. The sputtering sequence was taken from theSi process: It consists of a short period of Al sputtering with Argon, followed by sputtering of Al with N2,which results in AlN layers on sapphire. The sputter target was fixed at an angle of about (35±8)°. Just byshadowing, both (10-13) and (10-14) grains will form because of this large angle range. The AlN/sapphirewafers were annealed in metal-organic vapour phase epitaxy under NH3 at ~1200°C and then overgrownwith 10 nm of AlN, followed by 5-50 μm of GaN at 1080°C with a V/III ratio of 12.5.