Impact of thermal treatment on the growth of semipolar AlN on m-plane sapphire

Abstract

The interest in semipolar orientations has been increasing because the reduced piezoelectric field can improve the performance of nitride-based optoelectronic devices. However, the crystalline quality of semipolar AlN on m-plane sapphire is still not good enough to realize light emitters with sufficiently high efficiency. We performed high-temperature annealing on AlN on m-plane sapphire to improve the crystalline quality. For (10-1-3) and (11-22) AlN on m-plane sapphire, the crystalline quality improved as the annealing temperature was increased up to 1700 °C, whereas beyond 1750 °C the AlN layer started to deteriorate and desorb. The crystalline quality was further improved by additional growth of AlN. In addition, X-ray rocking curve measurements and transmission electron microscopy confirmed that the density of stacking faults was reduced after the additional growth of AlN.

Annihilation and Regeneration of Defects in (112̅2) Semipolar AlN via High-Temperature Annealing and MOVPE Regrowth

“…For MOVPE-grown semipolar AlN, the HTA technique was also utilized. 7,15 After thermal annealing, the full width half maximum (FWHM) value of X-ray ω-rocking curves (XRCs) of AlN was dramatically reduced, even though the absolute dislocation density is still much higher than that of c-plane AlN. 7 However, the defect annihilation mechanism is still unclear inside the semipolar AlN epitaxial layer, hindering further thin-film quality improvement.…”

“…Being highly stable and repeatable, high-temperature annealing (HTA) has attracted considerable attentions during dislocation annihilation in c -plane AlN thin films achieved by both metal–organic vapor-phase epitaxy (MOVPE) and physical vapor deposition (PVD). − A temperature as high as 1700 °C greatly enhances the surface diffusion of atoms near the defects, benefiting the recovery of crystal grains. For MOVPE-grown semipolar AlN, the HTA technique was also utilized. , After thermal annealing, the full width half maximum (FWHM) value of X-ray ω-rocking curves (XRCs) of AlN was dramatically reduced, even though the absolute dislocation density is still much higher than that of c -plane AlN . However, the defect annihilation mechanism is still unclear inside the semipolar AlN epitaxial layer, hindering further thin-film quality improvement.…”

Growth of Semi-Polar (101¯3) AlN Film on M-Plane Sapphire with High-Temperature Nitridation by HVPE

“…In contrast, the high temperature (>1200 °C) is beneficial to promote the coalescence of AlN grains, and thus improve the quality of AlN film [ 6 ]. Moreover, some research groups have obtained high-quality semi-polar AlN in the high-temperature region, ranging from 1200 to 1650 °C [ 8 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Jo et al obtained smooth (11 2) AlN with a thickness of 2 μm by metal organic chemical vapor deposition (MOCVD) at 1500 °C [ 21 ].…”

“…However, sapphire is easy to decompose in the atmosphere of NH 3 , N 2 and H 2 above 1200 °C [ 24 ]. Although low-temperature nitridation [ 19 ] is effective to prevent the decomposition of sapphire, there are still some reports showing that proper holes at sapphire surface can help reduce stress and achieve smooth surface of AlN film [ 25 , 26 ]. Furthermore, it is well-known that nitridation has a great influence on the orientation of semi-polar AlN [ 27 ].…”

“…Furthermore, it is well-known that nitridation has a great influence on the orientation of semi-polar AlN [ 27 ]. At present, the researches of nitridation temperature on semi-polar AlN are mainly focused on the low-temperature region [ 19 , 28 , 29 ]. Whether increasing nitridation temperature will help to reduce the stress and the surface roughness of AlN film remains to be discussed.…”