Designs Of High Quality GaN Epilayer Improved By New Patterned Sapphire Substrate And SiN_x Interlayer

As Ga N-based LEDs become more widely used,the requirements for device performance are becoming higher and higher,and we need to prepare high-quality Ga N epitaxial films to improve the optical and electrical properties of LED devices.Currently,we grow Ga N materials mainly by heteroepitaxial growth on sapphire substrates.Due to the large lattice mismatch between Ga N materials and sapphire,large extended defect will be generated in the epitaxial layer,affecting the crystal quality.The use of epitaxial lateral overgrowth technology is an effective method to improve the quality of crystals,but it requires an additional process during the growth of Ga N,resulting in higher production costs and lower efficiency.At present,it has been proposed that the technology evolved from lateral epitaxial overgrowth can improve the crystal quality while reducing additional external operations,such as patterned sapphire substrate?PSS?,in-situ Si Nx intercalation layer technology.On the other hand,the lattice mismatch between the sapphire substrate and the Ga N material not only results in the generation of extended defects,but also causes an increase in stress in the Ga N epitaxial layer,which stimulates the quantum confined Stark effect and reduces the optical performance.The effective solution to this problem is to grow semi-polar?11-22?plane Ga N capable of incorporating high indium components.The main work and conclusions are as follows:1. We designed a Si O₂-masked patterned sapphire substrates?SMPSSs?on the basis of PSS and the epitaxial Ga N layers on it with ultralow threading dislocation?TD?densities grown by metal organic chemical vapor deposition.The patterning employs periodic micro-scale Si O₂ cone-shaped features on thin sapphire pedestals surrounded by flat c-plane sapphire substrate surfaces.Cross-sectional transmission electron microscopy results demonstrate that Ga N films grown on SMPSSs provide an ultralow TD density of 8.5×10⁶ cm^-2.2. We design a single Si N_x interlayer method based on the standard in-situ deposition of Si N_x interlayer to grow a semi-polar?11-22?Ga N film with low defect density on an m-plane sapphire substrate.The linewidth of the X-ray diffraction rocking curves for our semi-polar Ga N films decrease with increasing Si N_x deposition time.Cross-sectional transmission electron microscopy analysis confirmed that this method greatly reduced the TD density of semi-polar Ga N film to 7×10⁸ cm^-2,which was two orders of magnitude less than that of conventionally deposited Ga N films.3. We also designed a method of double Si N_x intercalation layer on the basis of the standard in-situ deposition of the Si N_x interlayer to grow a semi-polar?11-22?Ga N film with significantly reduced defect density on an m-plane sapphire substrate.The X-ray rocking curve measurement results show that the semi-polar Ga N film has a relatively low full width at half maximum in the[11-23]and[10-10]directions,which is 0.119o.In addition,transmission electron microscopy analysis confirmed that the semi-polar Ga N film can significantly reduce the density of threading dislocations to 6×10⁸ cm^-2,which is two orders of magnitude less than conventionally deposited Ga N films.