V-pit to truncated pyramid transition in AlGaN-based heterostructures

Abstract

The formation of three-dimensional truncated pyramids after the deposition of AlN/GaN superlattices onto (0001) AlN/sapphire templates has been analysed by atomic force microscopy as well as transmission electron microscopy. V-pits in AlN layers and the formation of nanomounds around the v-pit edges are suggested to be responsible for the pyramid formation. Keeping the individual AlN layer thickness at 2.5 nm in the 80xAlN/GaN superlattice, the transformation to the three-dimensional pyramids is observed when the individual GaN layer thickness exceeds 1.5 nm. A subsequent overgrowth of the pyramidal structures by AlGaN results in inhomogeneous Ga distribution in the layers and laterally inhomogeneous strain states. Nevertheless, compared to the growth on planar layers, the overgrowth of the truncated pyramids leads to a slight reduction in dislocation density from 1 • 10 10 cm −2 (for GaN thickness of 1 nm in SL) to 7 • 10 9 cm −2 (for GaN thickness of 2 nm in SL). The non-planar growth front and thus the compositional inhomogeneity in AlGaN vanish gradually with increasing AlGaN thickness. As a result, homogeneous 4 μm thick Al 0.5 Ga 0.5 N buffer layers suitable for the fabrication of UV-B LED structures can be obtained.

Influence of the Growth Substrate on the Internal Quantum Efficiency of AlGaN/AlN Multiple Quantum Wells Governed by Carrier Localization

“…Such asymmetry causes growth instability and can lead to the kinetic formation of such step‐meandering. [ 20–22 ] This meandering induces a variation of the peak energy characterized by a standard deviation of 8 meV. Finally, it should be noted that no significant correlation between peak energy and CL intensity was found as shown in Figure 3c.…”

Indium incorporation in quaternary In x Al y Ga1−x−y N for UVB-LEDs

“…The investigated (In x )Al y Ga 1−x−y N layers were grown by metalorganic vapor phase epitaxy in a close coupled showerhead reactor. AlN/sapphire templates 13) are used as substrates with a subsequently grown AlN/AlGaN-superlattice (SL) for strain management and a relaxed Al 0.5 Ga 0.5 N buffer layer acting as a quasi-substrate 14,15) for further growth with a threading dislocation density of about 2 × 10 9 cm −2 . The (In x )Al y Ga 1−x−y N layers were grown with N 2 as carrier gas under a pressure of 400 mbar.…”

Effect of the GaN:Mg Contact Layer on the Light‐Output and Current‐Voltage Characteristic of UVB LEDs

“…Details on the growth of the n‐side layers can be found in Refs. and . The active region of the LED consists of a threefold Al 0.33 Ga 0.67 N/Al 0.44 Ga 0.56 N multiple‐quantum‐well (MQW) stack followed by a 25 nm thick Mg‐doped AlGaN electron blocking layer (EBL), a 150 nm‐thick Mg‐doped AlGaN/AlGaN superlattice with an average aluminum content of 42% and GaN:Mg contact layers with different thicknesses.…”