Inhomogeneous distribution of defect-related emission in Si-doped AlGaN epitaxial layers with different Al content and Si concentration

Abstract

The spatial distribution of luminescence in Si-doped AlGaN epitaxial layers that differ in Al content and Si concentration has been studied by cathodoluminescence (CL) mapping in combination with scanning electron microscopy. The density of surface hillocks increased with decreasing Al content and with increasing Si concentration. The mechanisms giving rise to those hillocks are likely different. The hillocks induced surface roughening, and the compositional fluctuation and local donor-acceptor-pair (DAP) emission at hillock edges in AlGaN epitaxial layers were enhanced irrespective of the origin of the hillocks. The intensity of local DAP emission was related to Si concentration, as well as to hillock density. CL observation revealed that DAP emission areas were present inside the samples and were likely related to dislocations concentrated at hillock edges. Possible candidates for acceptors in the observed DAP emission that are closely related in terms of both Si concentration and hillock edges with large deformations are a V III -Si III complex and Si N , which are unfavorable in ordinary III-nitrides. V C 2014 AIP Publishing LLC.

Optical Properties of Monodispersed AlGaN Nanowires in the Single-Prong Growth Mechanism

“…The three major factors affecting the blue shift in the band gap of the semiconductor nanomaterials are quantum confinement effect, , lowering temperature of the material, and alloying with appropriate elements. − It is reported that the exciton Bohr radius for GaN is 11 nm, so any role of the quantum confinement effect in elevating the band gap for as-prepared AlGaN NWs to 3.55 eV with an average diameter 50–100 nm can be ruled out. The reported band gap of GaN is 3.503 eV at 0 K. , Thus, the free exciton emission at 3.55 eV strongly confirms the presence of Al in the as-prepared NW sample (Figure ). The temperature-dependent study shows blue shift of the band gap with decreasing temperature (Supporting Information Figure S5).…”

Defect analysis in AlGaN layers on AlN templates obtained by epitaxial lateral overgrowth

“…Considering the atomically smooth surface as well as the low TDD in the ELO-AlN(a) template, this behavior might be explained by strain relaxation in thick Al 0.5 Ga 0.5 N layers through enhanced surface corrugation (transition to threedimensional (3D) growth). A similar effect has been frequently observed in AlGaN layers with increasing Ga content grown on planar AlN [25,26], where increasing compressive strain can be relaxed either through formation of additional dislocations and dislocation inclination (preferably for AlGaN with high Al content [24,27,28]) or through an enhanced surface roughening (preferably for low Al contents [25,26]). It should be emphasized that in our experiment we have applied the same deposition conditions for Al 0.5 Ga 0.5 N growth on both ELO-AlN(a) and ELO-AlN(m) templates.…”

Temperature Dependence of Dark Spot Diameters in GaN and AlGaN

“…The high linewidths for the AlGaN samples are mainly based on bandgap fluctuations caused by the statistical distribution of group‐III atoms and the small exciton radius in AlGaN. [ 31,32 ] In addition, the AlGaN composition can vary at certain growth features like growth islands, [ 33 ] hillocks, [ 34 ] or growth steps. [ 35,36 ] The latter effects are rarely present in sample C, but add to the broader emission linewidth in sample D, where the studied AlGaN layer is grown under a higher compressive strain.…”