Thickness and Mg doping of graded AlGaN layers: Influence on contact layer's structural and electrical properties for DUV emitters

Abstract

One of the methods to improve p-doping properties in (Al)GaN-based materials is using a technique called polarization doping. In our study, two sets of p-AlGaN contact layers with different thicknesses of the graded layer were deposited by metalorganic vapor phase epitaxy. The grown samples were investigated by atomic force microscopy, secondary ion mass spectrometry, X-ray diffraction and Hall effect measurements to study the influence of the thickness of the graded Al0.6→0Ga0.4→1N:Mg layer on the structural and the electrical properties of the whole grown structure. Additionally, theoretical calculations for the contact structures with different thicknesses of the p-Al0.6→0Ga0.4→1N graded layer were performed. The obtained results show that the concentration of p-type carriers on the p-GaN/p-AlGaN gradient interface decreases with increasing thickness of the graded layer. Our findings reveal that among the graded structures the highest concentration of holes, 1.2 × 1018 cm−3, was obtained for a structure with 50-nm-thick graded layer, while maintaining low sample resistivity. In addition, it was also shown that non-doping of the graded layer allows to improve electrical properties.