Surface morphology control of nonpolar m‐plane AlN homoepitaxial layers by flow‐rate modulation epitaxy

Abstract

We investigate the surface morphologies of nonpolar m‐plane AlN homoepitaxial layers grown by flow‐rate modulation epitaxy (FME). As source supply sequences, we employ a continuous supply and three types of FME: group‐III‐source FME, group‐V‐source FME, and FME with groups III and V alternated. We reveal that the average V/III ratio affects the step‐flow velocity in +c‐ and a‐directions, which determines step direction. In addition, steps toward the +c‐direction tend to bunch under N‐poor conditions. This is probably due to enhanced adatom migration resulting from the FME technique. Thus, we can control the surface morphologies of m‐plane AlN homoepitaxial layers and thereby obtain a flat surface with well‐aligned steps.

Kinetic instability of AlGaN alloys during MBE growth under metal-rich conditions on m-plane GaN miscut towards the -c axis

“…EDX elemental maps and Z-contrast STEM images show in both cases the compositional inhomogeneity of the AlGaN barriers. Figure 2 To examine the time dependence of the growth process in the instability regime, we have also grown a sample consisting of a sequence of five 3-period superlattices (sample B) with increasing AlGaN growth times (15,30,45, 60, and 75 s) and constant Al flux of 1.63 Â 10 14 atoms/cm 2 /s ( Fig. 3).…”

“…Sample B was grown to study the time evolution of the AlGaN structure in the instability regime. Sample B consists of five 3-period superlattices (B1-B5) with increasing AlGaN growth times (15,30,45, 60, and 75 s) and constant Al flux of 1.63 Â 10 14 atoms/cm 2 /s. Samples for STEM imaging and analysis were prepared using the focused ion beam (FIB) lift-out technique with a FEI Nova 200 DualBeam, and later thinned to transparency in a Nanomill at 900 eV.…”

“…27 Reference 28 provides a recent review of MOCVD growth of c-plane AlGaN for deepultraviolet LEDs. We also note that AlN and high Al-content AlGaN have also been grown by MOCVD on m-plane AlN, 29,30 and other substrates 31 with applications in UV emitters. 32 Bryan et al discussed the effects of surface kinetics on the composition distribution of c-plane AlGaN grown by MOCVD.…”

Semipolar (11–22) AlN Grown on m-Plane Sapphire by Flow-Rate Modulation Epitaxy for Vacuum-Ultraviolet Photodetection

“…It is worth noting that flow-rate modulation epitaxy (FME) has been demonstrated to be useful for reducing the defect density of polar AlN film grown on polar-plane (0001) sapphire, which leads to the increased migration abilities of the Al atom due to the interruption of NH 3 gas . Especially, Akasaka et al reported the improved surface morphologies of nonpolar AlN films grown by FME . However, few reports involve semipolar AlN films grown on m -plane sapphire by FME.…”

Sandwich method to grow high quality AlN by MOCVD

“…Another difficulty to grown AlN is strong parasitic gas phase pre-reactions between trimethylaluminum (TMAl) and ammonia (NH 3 ), which lead to reduced growth rate and degrade the surface morphology [20,21]. Different growth techniques have been proposed to decrease the parasitic pre-reactions between TMAl and NH 3 and to increase the adatom surface mobility such as the NH 3 pulsed flow [22], migration enhanced epitaxy [23], flowrate, modulation epitaxy [24], pulsed atomic layer epitaxy [25], etc. In this study, we have used the pulsed atomic layer epitaxy (PALE) method [26] to grow the initial high quality AlN layers.…”