The influence of an AlN seeding layer on nucleation of self-assembled GaN nanowires on silicon substrates

Abstract

Gallium nitride (GaN)-based nanowires (NWs) have attracted much attention for the fabrication of novel nanostructured devices. In this paper, the influence of an AlN seeding layer on the nucleation of self-assembled GaN NWs grown by plasma-assisted molecular beam epitaxy (MBE) on Si (111) substrates has been investigated. Not only is the formation of a twodimensional compact GaN layer at the bottom of the NWs suppressed, but also a high density of vertically aligned well-separated GaN NWs originating from GaN islands are successfully obtained after introducing annealing and nitridation processes. Scanning electronic microscope and transmission electron microscope measurements show that the NWs have a high crystalline wurtzite structure nearly free of dislocations and stacking faults and the NW diameter remains constant over almost the entire length. Due to the temperature-dependent diffusion length of Ga adatoms during the nucleation process, the formation of well-separated NWs relies on the distribution and morphology of the underlying AlN seeding layer. Moreover, the SiN x layer served as mask to inhibit coalescence at the nucleation sites. The developed growth processes and the obtained results provide a viable path facilitating the use of MBE growth techniques to fabricate III-nitride NW-based materials and related devices on Si substrates.

Crystal phase evolution in kinked GaN nanowires

“…Similar with reports on metal-catalysted GaN nanotubes/NWs and AlN NWs, these c-axis NWs with semipolar facets also show kinked morphology characteristics [34][35][36][37]. As shown by red arrows in figures 3(a), (d) and (e), the NW also consists of two alternate kinks by changing growth direction from [11][12][13][14][15][16][17][18][19][20][21][22][23] to [-1-123] or vice versa, [-1-123] to [11][12][13][14][15][16][17][18][19][20][21][22][23]) with the sidewall of {10-11} planes. The {10-11} planes are one of the lowest surface energy planes in GaN between the planes of {10-10} and {0001}.…”

“…Normally, the VLS-grown NWs grow perpendicularly to this growth plane. In contrast, there exists a non-orthogonal angle between the liquid-solid interface and growth direction for kinks along the [11][12][13][14][15][16][17][18][19][20][21][22][23]/[-1-123] direction, as illustrated in figures 4(d)-(e). The nonorthogonal angle is similar with Si 〈110〉 NWs, where the growth interface is observed to be {111} plane and the 〈112̅ 0〉 oriented GaN NWs have a {1-100}/liquid interface [45,46].…”

“…Compared to the common grown WZ structure, ZB structure has a higher crystallographic symmetry, which offers higher carrier mobility, easier p-type doping and no polarization effect [15]. With recent advances in crystal growth technology, GaN nanostructures have been synthesized through different methods and their growth direction, morphology, quality and growth mode can be well controlled [16][17][18][19][20][21][22]. Contrary to most of the III-V NW with their crystal phase to be controlled by the growth conditions, GaN NWs are dominant in WZ phase [22], though ZB phase inclusions as stacking faults (SFs) has been observed frequently [23][24][25].…”

AlGaN Quantum Disk Nanorods with Efficient UV-B Emission Grown on Si(111) Using Molecular Beam Epitaxy

“…A schematic of the AlGaN Qdisk nanorods is shown in Figure 1 a and a schematic diagram of the growth process is shown in Figure 1 b. The process was as follows: (Ⅰ) an AlN-seeding layer was deposited; (Ⅱ)vertically aligned GaN nanorods that were about 200 nm long were spontaneously formed at 780 ℃ [ 31 ]; (Ⅲ) AlGaN nanorod segments that were about 40 nm in length were deposited; (Ⅳ) by alternating the two Al cells, five pairs of Al x Ga 1−x N (2.5nm) / Al y Ga 1−y N (5nm) (x < y) Qdisks were grown as the active regions; (Ⅴ) the final 40-nm AlGaN nanorod segments were deposited. The Ga flux was maintained at 1 × 10 −7 Torr during the growth procedure and the Al flux varied from 3 × 10 −8 Torr to 8 × 10 −8 Torr.…”

Graphene-Based Transparent Conducting Substrates for GaN/AlGaN Nanocolumn Flip-Chip Ultraviolet Light-Emitting Diodes

“…In other words, nanocolumns can be grown on virtually any kind of substrates, and among these are amorphous materials and other non-conventional substrates, which can even provide alternative and low-cost options for commercialization. This is evidenced by the fact that the investigations of III-nitride nanocolumn synthesis not only have been extensively conducted on crystalline substrates − but also have been attempted on Ti, , Mo, , MoS 2 , Ta, Ti 3 C 2 , diamond, h-BN, Al x O y , and glass. − Going beyond the aforementioned materials, the proposition of utilizing two-dimensional materials as the substrate for nanocolumns may offer a unique approach in attaining greater flexibility and functionalities in future device configurations. So far, the formation of vertical III-nitride nanocolumns has been exclusively demonstrated on graphene, − but the importance of other two-dimensional materials, such as single- or few-layer MoS 2 , Ti 3 C 2 , and h-BN, as a substrate cannot be ignored, considering their distinct properties that can be favorable for a wide range of devices.…”