Mask-free three-dimensional epitaxial growth of III-nitrides

A novel catalyst-free and maskless growth approach is presented to form an ordered geometrical array of three-dimensional (3D) AlGaN/AlN microrods. The growth method is composed of a single growth step using metalorganic vapor phase epitaxy, achieving microstructures with homogeneous diameters, shapes and sizes over relatively large scale (on 2-in. wafer). The 3D AlGaN/AlN heterostructures are grown in a form of micro-sized columns elongated in one direction perpendicular to the substrate surface and with a hexagonal cross section. A careful examination of growth steps revealed that this technology allows to suppress coalescence and lateral overgrowth, promoting vertical 3D growth. Interestingly, two distinct morphologies can be obtained: honeycomb-like hexagonal arrangement perfectly packed and with twisted microrods layout, by controlling strain state in AlN buffer layers. Consequently, 3D AlGaN microrods on tensile-strained AlN templates show a 0 degrees twisted morphology, while on compressive-strained templated a 30 degrees twisted arrangement. Moreover, the optical and crystalline quality studies revealed that the top AlGaN layers of the examined 3D semiconductor structures are characterized by a low native point-defect concentration. These 3D AlGaN platforms can be applied for light emitting devices or sensing applications. Graphic abstract

Automated summary

A novel catalyst-free and maskless growth approach was proposed to form an ordered geometrical array of three-dimensional (3D) AlGaN/AlN microrods. By controlling the strain state in AlN buffer layers, two distinct morphologies can be obtained. This technology allows to suppress coalescence and lateral overgrowth, promoting vertical 3D growth, which is suitable for applications in light emitting devices or sensing.