Phase separation, atomic ordering and defects in quaternary indium aluminum gallium nitride epitaxial layers.

摘要

Phase separation, atomic ordering and defects including dislocations, inversion domain boundaries, and stacking faults were investigated in Indium Aluminum Gallium Nitride (InAlGaN) epitaxial layers grown on (0001) GaN/sapphire substrates using metalorganic chemical vapor deposition. Two lattice-mismatched and two lattice-matched InAlGaN layers were studied. Two ternary InGaN layers and two ternary AlGaN layers were also studied as references.; Phase separation was investigated using transmission electron microscopy (TEM). A comparison between quaternary InAlGaN layers and ternary InGaN layers, when they have similar indium compositions, suggested that driving force for phase separation in quaternary InAlGaN layers is larger than that in ternary InGaN layers. Around the InAlGaN/GaN interfaces, phase separation was suppressed due to the large coherent strain and the prohibited incorporations of both indium and aluminum by composition pulling. Atomic ordering rarely occurs in quaternary layers. Edge and mixed dislocations contribute most to the dislocations population with few screw dislocations. Most dislocations in GaN buffer layers replicate into InAlGaN layers. Dislocations can react with each other when they meet, which serves as a major mechanism of dislocations reduction. Run-to-run differences regarding inversion domain density were observed in InAlGaN/GaN layers. Differences in sapphire substrates regarding remnant surface defects and small deviations in GaN nucleation conditions, especially the nucleation temperature, might be responsible for the difference in inversion domain density. Dense three-layer zinc-blende stacking faults bounded by Shockley partials were observed in all the quaternary layers. Stacking faults densities in quaternary InAlGaN layers increased dramatically as compared with that in ternary InGaN layers, even when aluminum content is only 2%. Mass-contrast annular dark field (ADF) images showed that stacking faults are Al-rich in one InAlGaN layer, which has 12% of InN, 29% of AlN and 59% GaN. It is suggested that the low surface mobility of Al-containing radicals in the nitrogen environment led to stacking faults formation in quaternary InAlGaN layers.