Growth of N-polar In-rich InAlN by metal organic chemical vapor deposition on on- and off-axis sapphire. (15th March 2023) - Hasenöhrl, Stanislav
Abstract: Metal organic chemical vapor deposition is used to grow N-polar In-rich InAlN layers directly on on- and off-axis (misoriented by 4° towards a plane) c-plane sapphire substrates. During the InAlN growth, trimethylaluminum, ammonia, and the total flow was kept at 4.74 μmol/min, 3 slm and 10 slm, respectively, while trimethylindium (TMIn) flow was selected between 8.42 and 13.48 μmol/min. All samples were grown at about 706 °C however; TMIn flow of 10.95 μmol/min was also tested at the growth temperature of 686 °C. With increasing the TMIn flow, the In molar fraction increased from 0.55 to 0.69, irrespectively of the substrate miscut. For the moderate TMIn flow and In molar fraction of less than 0.63, density of screw and edge dislocations were from 0.3 to 12 ✕ 10 9 cm -2 and 5 to 7 ✕ 10 10 cm -2, respectively, while decisively lower densities appeared on on-axis structures. On the other hand, InAlN surface RMS roughness was from 1 to 8 nm favouring the off-axis substrate and low TMIn flow. Structural and surface deterioration appeared with the highest TMIn flow of 13.48 μmol/min and In molar fraction of 0.69, which hold also for reduced temperature of the growth. Nevertheless, room temperature photoluminescence full-width at half maximum less than 270 meV appeared for all samples, with maxima between 1.9 and 1.5 eV. In-rich N-polar InAlN grown on on-axis sapphire can be used as a buffer layer in new types of heterostructure devices. Highlights: MOCVD is used to grow N-polar In-rich InAlN layers directly on on- and off-axis c-plane sapphire substrates. With increasing the TMIn flow, the In molar fraction increased from 0.55 to 0.69, irrespectively of the substrate type. Decreased growth temperature below 690 ° C lead to InAlN surface roughening without affecting In content.