Preparation And Performance Of GaN-based LEDs Grown On Striped Sapphire Substrate And Silicon Substrate

The current range of applications of sapphire in the LED market is becoming more common due to its lower manufacturing costs.Nevertheless,the large lattice mismatch(15%)and thermal expansion coefficient mismatch(25%)between GaN(gallium nitride)films and sapphire substrates lead to high dislocation density and residual stress,which seriously reduces internal quantum.Efficiency and affects the performance of optical and electrical GaN-based LEDs.In order to improve the performance of GaN thin films grown on sapphire substrates,the performance of GaN-based LEDs is improved by using a patterned substrate to improve the crystal quality of GaN grown on the substrate and by finding alternative substrates.In this paper,we focus on the crystallinity of the c-plane GaN epitaxial layers grown on striped patterned sapphire substrates ablated by femtosecond laser.The surface morphology observed by SEM reveals the striped grooves in details which is the major factor to improve the crystallinity.By measuring the XRD,we obtained that the FWHM of striped sample is 0.302 ? which is much smaller than that of planar sample,while the crystallite size is 31.3 nm which is larger than that of the planar sample.Moreover,the little compressive stress is also found in GaN epitaxial layers by the measurement of Raman spectra.Compared with the planar substrate,the striped grooves help release the compressive stress and improve the crystallinity.The same result is also proved by the absorption spectra.The band gap of the striped PSS is estimated to be 3.43 eV.In conclusion,the PSS with striped grooves created by femtosecond laser ablation can improve the crystallinity of the c-plane GaN epitaxial layers.In this paper,GaN-based LEDs grown on silicon substrates and sapphire substrates are used as research sources.By comparing the temperature of the PN junction of two different substrate GaN-based LEDs and the reliability under extreme conditions,it is found that the silicon substrate PN junction has a lower junction temperature and better heat dissipation performance than the sapphire substrate LED.The aging test shows that the silicon substrate LED has better anti-attenuation performance than the sapphire substrate LED in the case where the aging time exceeds 1000 hours.