The Effect Of The Surface Adatom Migration Ability Enhancement On The Growth Of GaN

Gallium Nitride(GaN)has becoming a research hotspot,for its brilliant qualities like large bandgap,high electron saturation velocity etc.GaN has a huge value of application for electronic and optoelectronic devices.However,owing to the absence of single crystal GaN manufacture method,GaN could only be deposited on other materials,which would generate large amounts of dislocations in GaN films.For GaN-based optoelectronic devices,the dislocations in GaN films by heteroepitaxy could be the non-radiative combination centers,which lowers the eternal quantum efficiency.Thus,the crystal quality of GaN films by heteroepitaxty is needed to be further improved.As the development of the GaN growth,the most grow technology is growing GaN films on sapphire substrates by using metal oxide chemical vapor deposition(MOCVD).Nowadays the utilization of patterned sapphire substrate(PSS)and sputtered AlN nucleation layers could greatly improve GaN crystal quality,and it is widely applied in the manufacture of GaN-based light emitting diodes(LED).But the GaN growth mechanism on sputtered AlN/PSS templates is not thoroughly understood.Under the investigation,we found that when GaN grown on 10 nm,25nm,and 40 nm sputtered AlN/PSS templates,the growth differs very much at the early stage:on 10 nm sputtered AlN/PSS templates,GaN mainly grows on the pattern and large GaN grains forms on it;on 25 nm sputtered AlN/PSS templates,GaN mainly nucleates and grows on the space areas between patterns,and some small GaN grains form on the bottom of the patterns,which would be merged soon during the growth;on 40 nm sputtered AlN/PSS templates,GaN mainly grows on the space areas,and some small GaN grains form on the top of the patterns,which could grow larger as the growth proceeds.We characterize the templates with sputtered AlN of different thickness,and grow GaN on planar substrates with 10 nm,25 nm,and 40 nm sputtered AlN.We found that there is no effective sputtered AlN on the patterns of 10 nm sputtered AlN/PSS templates.Most importantly,we conclude that the migration ability of Ga atoms enhances as the thickness of sputtered AlN increases.The two conclusions together explains the disparity of GaN growth on the 10 nm,25 nm,and 40 nm sputtered AlN/PSS templates.After the deposition of 5 μm GaN films,the results show that the disparity of GaN growth at early stages leads to the different qualities of GaN films:GaN on 10 sputtered AlN/PSS template cannot coalesce well,which means the crystal quality is severely damaged.The GaN film on 40 sputtered AlN/PSS templates has inferior crystal quality,compared with the GaN film on 25 nm sputtered AlN/PSS templates.Therefore,we prove that the migration ability of adatoms on the surface has great influences on the GaN growth on sputtered AlN/PSS templates,by effecting the GaN growth at the early stage.Then we also grow InGaN/GaN-based LED structures on the 10 nm,25 nm,and 40 nm sputtered AlN/PSS templates.After characterization,we found that different migration ability of adatoms also effect the crystal quality and performance of InGaN/GaN-based LED on sputtered AlN/PSS templates.Moreover,the incoproration of Indium atoms would also be influences,leading to the wavelength shift of the InGaN/GaN-based LEDIn this paper,the HRXRD results at(002)/(102)planes of 5 μm GaN film and InGaN/GaN based LED on the 25 nm sputtered AlN/PSS template is 87/144 arcsec and 91/144 arcsec respectively,whose crystal quality is word leading.Therefore we consider that it is very important to optimize the thickness of sputtered AlN nucleation layers,to make adatoms on the surface have appropriate migration ability.Then,the quality and GaN film and the performance of InGaN/GaN based LED could be greatly improved.