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Performance-improved vertical GaN-based light-emitting diodes (LEDs) have been fabricated on Si substrates through designing the epitaxial structures with a combination of an AlN interlayer and a SiNx interlayer. The AlN interlayer is used to introduce more compressive stress in GaN epitaxial films to balance the tensile stress formed in thick n-GaN epitaxial films from cracking, and the SiNx interlayer is employed to annihilate the dislocation density to improve the crystalline quality of GaN epitaxial films. By using the optimized epitaxial structures, high-quality crack-free GaN-based LED wafers have been obtained. The full-widths at half-maximum from the GaN(0002) and GaN(10−12) X-ray rocking curves are as small as 280 arcsec and 310 arcsec, respectively. The hetero-interfaces of the InGaN/GaN multiple quantum wells are sharp and abrupt. After the LED wafers are fabricated into vertical LED chips, they reveal high-performance with a high light output power of 595 mW and a small working voltage of 2.75 V with an electroluminescence dominant wavelength of 456 nm @ 350 mA, corresponding to a wall-plug efficiency (WPE) as high as 61.8%. These performance-improved vertical LED chips open a broad prospect in the application of high-end lighting applications.

The epitaxial structures of GaN films grown on AlN/Al heterostructures by pulsed laser deposition (PLD) are designed with and without an amorphous AlN layer, and quality-enhanced crack-free GaN epitaxial films are obtained. Compared with GaN epitaxial films grown without inserting the amorphous AlN layer, by inserting a ∼5 nm-thick amorphous AlN layer in GaN, the residual stress in ∼600 nm-thick GaN epitaxial films is greatly reduced from −0.81 to −0.19 GPa, and high-density dislocations are annihilated in the amorphous AlN layer. The full-width at half-maximum for GaN(0002) and GaN(10-12) decreases from 1.1° and 1.2° to 0.90° and 0.98°, respectively. The root-mean-square surface roughness of as-grown GaN epitaxial films is also decreased from 3.5 to 1.5 nm. Evidently, the amorphous AlN layer can release the stress and trap the dislocations, preventing them from extending into the upper layer, as well as improve the surface morphology of GaN epitaxial films. Moreover, the nucleation mechanism of dislocation formation and annihilation in GaN epitaxial films grown on AlN/Al heterostructures by PLD with an amorphous AlN layer is hence proposed. These quality-enhanced GaN epitaxial films are of paramount importance for the application of GaN-based optoelectronic devices.

A high-quality AlN epitaxial film has been grown on a Si(111) substrate by metal–organic chemical vapor deposition through designing the AlN nucleation layer. The structure of a low temperature nucleation layer hinders the formation of amorphous SiNx in the AlN/Si heterointerface, reduces the dislocation density, and thereby improves the crystalline quality of the AlN epitaxial film. The influence of nucleation layer temperature on the surface morphology and the crystalline quality of the AlN epitaxial film is also revealed in detail. The AlN epitaxial film with the optimized nucleation layer grown at a temperature of 800 °C shows a sharp AlN/Si heterointerface, with an XRD full-width at half-maximum for AlN(0002) of 0.30°, and a very smooth surface with a root-mean-square surface roughness of 1.9 nm. Meanwhile, the 200 nm-thick AlN epitaxial film is almost fully relaxed with an in-plane tensile strain of only 0.42%. This work provides an effective approach for the growth of high-quality AlN epitaxial films in the application of AlN-based ultraviolet photonic devices and GaN-based optoelectronic devices.

The anisotropic surface etching behavior of nonpolar a-plane GaN (110) epitaxial films, grown by pulsed laser deposition, was investigated experimentally by wet chemical etching. Crystal-orientation dependent face state, induced by anisotropic growth kinetics, is the origination of the anisotropic properties of the a-plane GaN epitaxial films. Defects that propagate into the surface offer initial positions for the etching process. A joint effect of two factors determines the etching-exposed surface morphology, primarily including triangular prisms and pits, thus making wet chemical etching a promising tool for the investigation of defect distribution. Type I1 basal stacking faults and partial dislocations are proven to have a direct connection with etching-exposed triangular prisms and pits, respectively. This study presents a mechanism research from the standpoint of the evolution process of the surface morphology during the etching process and brings insight for further understanding of the anisotropic properties of the nonpolar GaN epitaxial films for the realization of a high polarization light-emission device, which has a broad application in display and backlighting.

High-quality AlN epitaxial films have been epitaxially grown on Cu(111) substrates by pulsed laser deposition (PLD) through effectively controlling the interfacial reactions between AlN epitaxial films and Cu substrates. The interfacial properties of the as-grown AlN/Cu hetero-interfaces and their formation mechanisms have been systemically studied. A 2.1 nm-thick CuxAl1−xN interfacial layer is formed in AlN/Cu hetero-structures at a high growth temperature of 600 °C, while abrupt and sharp AlN/Cu hetero-interfaces with no interfacial layer are achieved by effectively controlling the interfacial reactions at a low growth temperature of 450 °C. The as-grown ∼300 nm-thick AlN epitaxial films grown at 450 °C show very smooth surfaces with a root-mean-square surface roughness of 1.2 nm and high crystalline quality with full-width at half-maximum values of X-ray rocking curves for AlN(0002) and AlN(10−12) of 0.7° and 0.8°, respectively. Meanwhile, the residual stress in the as-grown AlN epitaxial films is also well controlled through low temperature growth with a residual compressive stress of 0.30 GPa. These high-quality AlN epitaxial films are of paramount importance for the commercial development of high-performance AlN-based optoelectronic devices.