III-nitride wide bandgap semiconductors are promising materials for modern optoelectronics and electronics. Their application has progressed greatly thanks to the continuous quality improvements of heteroepitaxial films grown on large-lattice-mismatched foreign substrates. But compared with bulk single crystals, there is still tremendous room for the further improvement of the material quality. Here we show a paradigm to achieve high-quality III-nitride heteroepitaxial films by the controllable discretization and coalescence of columns. By adopting nano-patterned AlN/sapphire templates with regular hexagonal holes, discrete AlN columns coalesce with uniform out-of-plane and in-plane orientations guaranteed by sapphire nitridation pretreatment and the ordered lateral growth of cleavage facets, which efficiently suppresses the regeneration of threading dislocations during coalescence. The density of dislocation etch pits in the AlN heteroepitaxial film reaches 3.3 × 104 cm-2, close to the present available AlN bulk single crystals. This study facilitates the growth of bulk-class quality III-nitride films featuring low cost and scalability.

The atomic-layer misorientation during the growth of a 5 mu m thick AlN thin film on a patterned (0001) sapphire substrate was investigated by the scan rotation approach using a probe aberration-corrected scanning transmission electron microscope at a nanometer scale. Through the geometrical phase analysis of the resulting twisted atomic structure at different depths below the top surface, it is shown that over 10% of local tensile and compressive strain is balanced in a 1.6 degrees twist of the c-planes within the first micron of AlN growth. As a consequence, the formation of threading dislocations is reduced. The in-plane twist is seen to decrease toward the layer surface down to 0.5 degrees. Finally, growth has adopted the conventional step flow mechanism with a reduced density of emerging dislocations by the thickness of 5 mu m. Our finding forecasts the possibility of understanding the relationship between atomic bilayer twist and local strain accommodation at a nanometer scale, which could provide guidance for achieving better crystal quality of AlN thin films on patterned substrates during epitaxy.

Growth of AlGaN-based multiple quantum wells (MQWs) with an IQE > 80% at room temperature has been realized on nano-patterned sapphire substrates. A DUV-LED device is then fabricated taking such high IQE MQWs as the active region.

Hall data for a p-Al0.4Ga0.6N/Al0.67Ga0.33N superlattice layer. The hole concentration in this p-AlGaN superlattice layer is 3.7×1018 cm-3 at room temperature.

We have investigated the growth of AlN films on hexagonal nano-concave-circle patterned Si substrates using metal–organic chemical vapor deposition. By depositing a thin AlN seed layer on the Si substrate before the pattern process, a high quality AlN film with a thickness of 2 μm has been obtained. The full width at half maximum values of X-ray diffraction rocking curves are as low as 409 and 677 arc sec for AlN (002) and (102) planes, respectively. Further experimental results indicate that the AlN seed layer can suppress the misorientation of the adjacent grains, as revealed by the lower twist and tilt angles of the mosaic structure, and thus only a few dislocations generated during the grain coalescence. In addition, the migration of Al adatoms is enhanced on the Al terminated surface of the AlN seed layer, which accelerates the coalescence process. All these improvements are attributed to the lower binding energy and diffusion barrier for Al adatoms on the Al terminated surface than that on the Si surface. Our results demonstrate an effective approach to obtain high quality AlN films for high performance ultraviolet light-emitting diodes on the Si substrate.

Quantum technologies require robust and photostable single-photon emitters. Here, room temperature operated single-photon emissions from isolated defects in aluminum nitride (AlN) films are reported. AlN films were grown on nanopatterned sapphire substrates by metal organic chemical vapor deposition. The observed emission lines range from visible to near-infrared, with highly linear polarization characteristics. The temperature-dependent line width increase shows T3 or single-exponential behavior. First-principle calculations based on density functional theory show that point defect species, such as antisite nitrogen vacancy complex (NAlVN) and divacancy (VAlVN) complexes, are considered to be an important physical origin of observed emission lines ranging from approximately 550 to 1000 nm. The results provide a new platform for on-chip quantum sources.

The stress evolution behavior of AlN grown on nano-patterned substrates (NPSSs) has been investigated. It is found that there are two sources of the tensile stress for AlN grown on NPSSs. One originates from the coalescence of grain islands of the AlN nucleation layer, and then the voids provide a channel for the gradual release of the tensile stress to nearly stress-free state accompanied by the lateral growth process of the AlN columns on the mesas. The other originates from the contacting of adjacent columns to complete the coalescence process, which is responsible for the residual tensile stress in the top AlN epilayer after completing the coalescence. This understanding of the stress evolution is certainly of great significance in AlN-based material and devices.

A comprehensive strategy of crystal quality control for AlN grown on a nano-patterned sapphire substrate has been explored based on the period size effect. It is found that the crystalline perfection of AlN can be greatly improved by enlarging the period size from 1.0 to 1.4 μm, and the X-ray diffraction ω-scan FWHM values for (0002) and (10-12) planes reach 162 and 181 arcsec, respectively, owning to the significantly reduced area ratio of the coalescence zone. Our results indicate the pattern design requires a critical balance between reducing the area ratio of the coalescence zone and decreasing the coalescence thickness.

In this work, a novel strategy for high-quality AlN templates epitaxy on sapphire substrates with sputtered buffer layers combined with a low- and high-temperature alteration technique is proposed. The best full width at half maximum values for (0002) and (11¯02) reflections are 207 and 377 arcsec, respectively. Investigations indicate the joint effect of growth mode control and sputtered buffer layer results in the improvement of AlN crystalline quality. Firstly, threading dislocations density can be significantly decreased due to the alteration from three-dimensional to two-dimensional growth mode. Moreover, the graded composition of AlON layer in the sputtered buffer layer is believed to alleviate lattice mismatch between sapphire substrates and AlN, which also contributes to low dislocations density in AlN templates.