Light emission and microstructure of Mg-doped AlGaN grown on patterned sapphire

Abstract

Distinct crystalline and optical properties have been observed in Mg-doped Al0.03Ga0.97N grown on a patterned sapphire substrate; the pattern consisting of etched trenches along the sapphire 〈112̄0〉 direction. The epilayer has two distinct regions: one grown directly onto the sapphire mesa and the other an epitaxial lateral overgrowth (ELO) region that overhangs the trench. Transmission electron microscopy shows the presence of pyramidal defects as well as large dislocation densities in the region grown directly on sapphire. In contrast, the ELO region is defect free and contains no Mg-related pyramidal defects. Cathodoluminescence measurements show superior near-band-edge emission in the ELO region, suggesting that the emission is susceptible to nonradiative centers caused by the high defect density in the rest of the sample. The Mg-related donor–acceptor-pair emission is fairly uniform throughout the film, indicating that it is not affected by the nonradiative centers. These optical and structural properties of AlGaN are closely related to the direction of the growth front.

Crystal growth and p‐type conductivity control of AlGaN for high‐efficiency nitride‐based UV emitters

“…Therore, with increasing Mg concentration, the hole concentration at RT superlinearly increases [13][14][15]. However, if Mg is overdoped, defects such as an inversion domain boundary are generated which may induce compensation centers causing activation energy to increase and hole concentration to decreasea sharply [16,17]. Therefore, there is a maximum hole concentration in the whole compositional range.…”

Spatially resolved cathodoluminescence study on AlGaN layer fabricated by air‐bridged lateral epitaxial growth

“…However these devices are composed of AlGaN-based III-V nitrides with higher Al content and the large lattice mismatch between GaN and AlGaN degrades the crystalline quality of AlGaN layers. It is difficult that the TDs in AlGaN layers are reduced by the ELO technique because of nucleation of poly-crystals on the mask surface [11][12][13][14]. Furthermore, the AlGaN layer is susceptible to fluctuations of Al content, which lead to fluctuations of the lattice constant and generate the local stress.…”

Thick crack‐free AlGaN films deposited by facet‐controlled epitaxial lateral overgrowth

“…Using a low temperature buffer layer and patterned sapphire substrates, thick crack-free AlGaN films can be grown with reduced dislocation densities [2]. However, the material quality degrades fast with increasing Al content [3].…”