Characteristics Comparison between GaN Epilayers Grown on Patterned and Unpatterned Sapphire Substrate (0001)

Abstract

GaN epilayers were grown on lens shaped patterned sapphire substrate (PSS) (0001) and unpatterned sapphire substrate (UPSS) (0001) by metal-organic chemical vapor deposition (MOCVD). The quality of the grown GaN epilayers on the PSS and UPSS were compared. Structural characteristics, surface morphology and optical properties of the GaN epilayers were investigated using double crystal X-ray diffraction (DCXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence (PL). A lens shaped pattern was formed on the sapphire substrate to reduce threading dislocation (TD) density and also to improve the optical emission efficiency by internal reflection on the lens. Scanning electron microscopy images show the growth of GaN epilayers at various times. Full coalescence is observed at a growth time of 80 min. It is seen from the DCXRD rocking spectrum that full width at half maximum (FWHM) of the GaN grown on PSS was 438.7 arcsec which is less than UPSS value. The lower value of FWHM indicates that the crystalline quality of the GaN epilayers grown on PSS is improved compared to GaN grown on UPSS. It is clearly seen from the AFM images that the dislocation density is less for the GaN grown on PSS. A strong and sharp photoluminescence (PL) band edge emission was observed for the GaN grown on PSS compared to UPSS. Defect related yellow luminescence was observed for GaN grown on UPSS which did not appear for PSS. The FWHM at the 364.3 nm peak position was evaluated to be 50.7 meV from the PL spectra for GaN grown on PSS. The above result indicates GaN epilayers can be grown on PSS with low TD density and will be useful for optical emission.

High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

“…Particularly, III-nitride based vertical devices, such as vertical-cavity surface-emitting lasers (VCSELs), are costly and challenging to produce, thus compromising on the efficiency obtained. For example, the efficiency of devices grown on Al 2 O 3 is threatened by the introduction of high threading dislocation density (TDD) 4 5 due to a large lattice mismatch (14%) and a large difference in thermal expansion coefficients between III-nitride semiconductor and the substrate 6 7 . This high TDD causes many nonradiative recombinations and scattering centers, which will deteriorate the optical and electrical quality of III-nitride devices 8 .…”

Comparative Research of GaN Growth Mechanisms on Patterned Sapphire Substrates with Sputtered AlON Nucleation Layers

“…The cross-sectional SEM images of GaN films on 10, 25, and 40 nm sputtered AlON/PSS templates were taken from the [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ] direction, presented in Figure 5 . From the cross-sectional SEM image of the GaN film on the 10 nm sputtered AlON/PSS template, we could clearly observe that GaN could not coalesce well.…”

“…The utilization of PSSs could greatly annihilate dislocations [ 4 , 7 , 8 , 9 ]. Interestingly, with the appropriate nucleation layer (NL), most GaN grows in the flat regions between cones, though the flat region is a rather small proportion of the whole substrate, no matter what the geometry of the pattern is [ 10 , 11 , 12 ]. However, some GaN would still form small GaN crystals on the cone sidewalls, which may have negative influences on GaN growth [ 13 , 14 ].…”

Epitaxy of III-Nitrides on β-Ga2O3 and Its Vertical Structure LEDs

“…The widely used sapphire (Al 2 O 3 ) substrate has large lattice mismatch (14% with GaN) and large thermal expansion coefficient mismatch (30% with GaN) with III-Nitrides materials [30,31,32], which will introduce high threading dislocation density (TDD) [32,33] acting as nonradiative recombination and scattering centers that deteriorate the performance of LEDs [34]. Furthermore, LEDs are fabricated in a horizontal structure since the sapphire substrates are insulated, leading to that both the n- and p-contact must be established at the top surface of the devices.…”