A Study On Dislocation In Si Substrate GaN Thin Films And Passivation Layer Of LED Device

Compared with sapphire and SiC substrates,Si has larger thermal and lattice mismatch with GaN,that brings tough challenge to epitaxy growth and reliability of GaN based LED on Si substrate.This dissertation focus on tow major directions including the influence of SiN passivation layer to the GaN based blue LED on Si substrate and the study on dislocation density of GaN epitaxy layer.The main results of our research are as following:1.During the deposition of SiN passivation layer,a great number of H ions have diffused into p-GaN in the sidewall vicinity,engendered H-Mg complex which greatly reduce the conductivity of the sidewall and the odds of dislocation diffusion during the LED's performance,thus increase the V_r value after aging.Contributing to the H-Mg complex which brings deep level in the GaN band and then increase the transition probability of electron,the wafer get small VF1 after the deposition of SiN passivation layer.2.Compact SiN passivation layer brings compression stress on the GaN epitaxy layers,which prevents the piezoelectricity filed from being deteriorated and finally reduces the luminous decay of GaN based LED on Si after aging.The result that the SiN passivation layer has the effect in reducing luminous decay of GaN based LED was never reported in former reports.3.XRD test results of sample A indicate that the density of screw dislocation in GaN epitaxy layer is 2.77×10⁸cm^-2 and the edge one is 2.23×10⁹cm^-2,It proves that the density of dislocation in GaN-based LED on Si was basically same order of magnitude as that in GaN LED on sapphire or SiC substrates.The investigation of defects on the top of the epitaxy layers was carried out by AFM,From the AFM graphs.We can get the precise date of the defects density and aperture,which can effectively reflect the growth quality of GaN.4.The investigation of defects by the means of H₃PO₄ wet etch was carried out to both blue and green GaN-based LED on Si.According to the theory that big etch pits connected with screw dislocation and small pits to edge dislocation,we found the density of edge dislocation in all samples is about one or two orders of magnitude more than that the density of screw type.And compared with green GaN-based LED, the density of screw dislocations is a little bit higher and edge-type is a little bit lower in the blue GaN-based LED epitaxy.