High-Quality GaN Epilayers Achieved by Facet-Controlled Epitaxial Lateral Overgrowth on Sputtered AlN/PSS Templates

Abstract

It is widely believed that the lack of high-quality GaN wafers severely hinders the progress in GaN-based devices, especially for defect-sensitive devices. Here, low-cost AlN buffer layers were sputtered on cone-shaped patterned sapphire substrates (PSSs) to obtain high-quality GaN epilayers. Without any mask or regrowth, facet-controlled epitaxial lateral overgrowth was realized by metal-organic chemical vapor deposition. The uniform coating of the sputtered AlN buffer layer and the optimized multiple modulation guaranteed high growth selectivity and uniformity of the GaN epilayer. As a result, an extremely smooth surface was achieved with an average roughness of 0.17 nm over 3 × 3 μm. It was found that the sputtered AlN buffer layer could significantly suppress dislocations on the cones. Moreover, the optimized three-dimensional growth process could effectively promote dislocation bending. Therefore, the threading dislocation density (TDD) of the GaN epilayer was reduced to 4.6 × 10 cm, which is about an order of magnitude lower than the case of two-step GaN on the PSS. In addition, contamination and crack in the light-emitting diode fabricated on the obtained GaN were also effectively suppressed by using the sputtered AlN buffer layer. All of these advantages led to a high output power of 116 mW at 500 mA with an emission wavelength of 375 nm. This simple, yet effective growth technique is believed to have great application prospects in high-performance TDD-sensitive optoelectronic and electronic devices.

Defect-rich GaN interlayer facilitating the annihilation of threading dislocations in polar GaN crystals grown on (0001)-oriented sapphire substrates

“…[20][21][22] In a recent publication, Stanchu et al described the positive effect of compositionally graded AlGaN buried layers in GaN/AlGaN/GaN stacks on the lattice strain relaxation and on the annihilation of TDs. 23 Among the nowadays actively developed techniques which support bending and bunching of the TDs in GaN, the selective area growth (SAG), [24][25][26][27][28] the epitaxial lateral overgrowth (ELO), [29][30][31][32][33] and the facet-controlled epitaxial lateral overgrowth (FACELO) [34][35][36] are to be mentioned.…”

Comparative Research of GaN Growth Mechanisms on Patterned Sapphire Substrates with Sputtered AlON Nucleation Layers

“…The size of GaN crystals on the 40 nm sputtered AlON/PSS template increased from 0.54 μm to 0.70 μm by our measurement. It could be inferred that GaN crystals on the 40 nm sputtered AlON/PSS template had more chances to grow, and generated more dislocations [ 15 , 20 , 21 ].…”

“…Subsequently, many works proved that the utilization of sputtered AlN/PSS templates could improve the performance of GaN-based LEDs [ 18 , 19 ]. However, small GaN crystals on the cones’ surface of sputtered AlN/PSS templates may still deteriorate the crystal quality [ 15 , 20 , 21 ]. The study of small GaN crystals on sputtered AlN/PSS templates is beneficial to further improve the crystal quality.…”

Investigation of AlGaN/GaN Heterostructures Grown on Sputtered AlN Templates with Different Nucleation Layers

“…Such issues have motivated the use of various nucleation layers (NL) in the GaN epitaxy on sapphire substrates. Among them, the sputtered AlN template on a sapphire substrate has attracted significant attention because the sputtering process supports a high throughput, is largely scalable, is inexpensive, and has been shown to give rise to reduced dislocation densities in the GaN grown thereon [11][12][13]. In terms of device performance, sputtered AlN films have been demonstrated to provide notable improvements in terms of increased light output, lower forward turn on voltage, reduced reverse leakage current, and improved reliability for visible and ultraviolet-light-emitting diodes [14,15].…”