Evolutionary growth of microscale single crystalline GaN on an amorphous layer by the combination of MBE and MOCVD

Abstract

To integrate multiple functional devices on a chip, advances in epitaxial growth on heterosubstances are required. As one approach to achieve an epitaxial layer on an amorphous substrate, we developed a method of combined epitaxial growth using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). This two-stage combined growth can be used to grow a binary gallium nitride (GaN) on any thermally durable substances. The first MBE growth step provided us effective nucleation with uniform morphology. Meanwhile, the second MOCVD growth enabled improved crystalline quality. Detailed analysis at grain-to-grain and layer-to-layer interfaces was studied with high-resolution transmission electron microscopy (TEM) characterization. This study gives a deep understanding of the growth behavior, thereby supporting the demonstration of perfect single crystalline GaN, enabling the realization of optoelectronic GaN-based devices on amorphous layer.

III-nitride core–shell nanorod array on quartz substrates

“…5c. However, we have observed that the crystallinity of the buffer GaN becomes worse as the growth temperature is abruptly increased in the MOCVD system due to thermal re-crystallisation27. On the other hand, GaN NRs stood out as zone II grain features in the SZM with strong selective orientation since both the surface and bulk diffusion are significantly active at such a high homogenous temperature of ~0.535.…”

“…5d tended to grow along the surfaces of the wetting layers. Previously, we had related the initial nucleation mechanism on the amorphous layer to Ga 2 O 3 nanoclusters27. Similar growth behaviours might be induced at the interface of the GaN buffer and quartz substrates, as we used the same epitaxy system and substrates.…”

“…6a were almost identical to the grain size (~a few hundreds of nanometre) of the GaN buffer. We have already reported mixed polarity in the GaN buffer grown by MBE27. In addition, undulated surfaces are prone to polarity inversion by atomic rotation during growth of the first few GaN monolayers40.…”

“…Note that no remarkable threading dislocations (TDs) penetrated the interior of the GaN NRs from the GaN buffer, indicating suppression of abrupt strain relaxations at the interface. This is an important advantage of nanoscale SAG procedures, as previous epitaxy on amorphous substrate frequently generated high density of stacking faults (SFs) and grain boundaries (GBs) in the upper-grown GaN structures2527. Figure 5d is a more detailed TEM image of the interface between the GaN buffer and quartz substrates.…”

“…nanoscale SAG) to improve the crystal quality of GaN on amorphous layers. Recently, we reported that GaN layers can evolve on amorphous substrates through microscale SAG with striped openings, where a relatively smooth GaN buffer layer was grown by MBE without a POL27. However, although the crystal quality in the previous stage is improved, it is still far from realising optoelectronic devices on amorphous substrates due to the high level of structural defects.…”